Documentation/networking/stmmac.txt - kernel/msm-4.9 - Gitiles

        STMicroelectronics 10/100/1000 Synopsys Ethernet driver

 Copyright (C) 2007-2010  STMicroelectronics Ltd
 Author: Giuseppe Cavallaro <peppe.cavallaro@st.com>

 This is the driver for the MAC 10/100/1000 on-chip Ethernet controllers
 (Synopsys IP blocks).

 Currently this network device driver is for all STM embedded MAC/GMAC
 (i.e. 7xxx/5xxx SoCs), SPEAr (arm), Loongson1B (mips) and XLINX XC2V3000
 FF1152AMT0221 D1215994A VIRTEX FPGA board.

 DWC Ether MAC 10/100/1000 Universal version 3.60a (and older) and DWC Ether
 MAC 10/100 Universal version 4.0 have been used for developing this driver.

 This driver supports both the platform bus and PCI.

 Please, for more information also visit: www.stlinux.com

 1) Kernel Configuration
 The kernel configuration option is STMMAC_ETH:
  Device Drivers ---> Network device support ---> Ethernet (1000 Mbit) --->
  STMicroelectronics 10/100/1000 Ethernet driver (STMMAC_ETH)

 2) Driver parameters list:
 	debug: message level (0: no output, 16: all);
 	phyaddr: to manually provide the physical address to the PHY device;
 	dma_rxsize: DMA rx ring size;
 	dma_txsize: DMA tx ring size;
 	buf_sz: DMA buffer size;
 	tc: control the HW FIFO threshold;
 	tx_coe: Enable/Disable Tx Checksum Offload engine;
 	watchdog: transmit timeout (in milliseconds);
 	flow_ctrl: Flow control ability [on/off];
 	pause: Flow Control Pause Time;
 	tmrate: timer period (only if timer optimisation is configured).

 3) Command line options
 Driver parameters can be also passed in command line by using:
 	stmmaceth=dma_rxsize:128,dma_txsize:512

 4) Driver information and notes

 4.1) Transmit process
 The xmit method is invoked when the kernel needs to transmit a packet; it sets
 the descriptors in the ring and informs the DMA engine that there is a packet
 ready to be transmitted.
 Once the controller has finished transmitting the packet, an interrupt is
 triggered; So the driver will be able to release the socket buffers.
 By default, the driver sets the NETIF_F_SG bit in the features field of the
 net_device structure enabling the scatter/gather feature.

 4.2) Receive process
 When one or more packets are received, an interrupt happens. The interrupts
 are not queued so the driver has to scan all the descriptors in the ring during
 the receive process.
 This is based on NAPI so the interrupt handler signals only if there is work
 to be done, and it exits.
 Then the poll method will be scheduled at some future point.
 The incoming packets are stored, by the DMA, in a list of pre-allocated socket
 buffers in order to avoid the memcpy (Zero-copy).

 4.3) Timer-Driver Interrupt
 Instead of having the device that asynchronously notifies the frame receptions,
 the driver configures a timer to generate an interrupt at regular intervals.
 Based on the granularity of the timer, the frames that are received by the
 device will experience different levels of latency. Some NICs have dedicated
 timer device to perform this task. STMMAC can use either the RTC device or the
 TMU channel 2  on STLinux platforms.
 The timers frequency can be passed to the driver as parameter; when change it,
 take care of both hardware capability and network stability/performance impact.
 Several performance tests on STM platforms showed this optimisation allows to
 spare the CPU while having the maximum throughput.

 4.4) WOL
 Wake up on Lan feature through Magic and Unicast frames are supported for the
 GMAC core.

 4.5) DMA descriptors
 Driver handles both normal and enhanced descriptors. The latter has been only
 tested on DWC Ether MAC 10/100/1000 Universal version 3.41a and later.

 STMMAC supports DMA descriptor to operate both in dual buffer (RING)
 and linked-list(CHAINED) mode. In RING each descriptor points to two
 data buffer pointers whereas in CHAINED mode they point to only one data
 buffer pointer. RING mode is the default.

 In CHAINED mode each descriptor will have pointer to next descriptor in
 the list, hence creating the explicit chaining in the descriptor itself,
 whereas such explicit chaining is not possible in RING mode.

 4.6) Ethtool support
 Ethtool is supported. Driver statistics and internal errors can be taken using:
 ethtool -S ethX command. It is possible to dump registers etc.

 4.7) Jumbo and Segmentation Offloading
 Jumbo frames are supported and tested for the GMAC.
 The GSO has been also added but it's performed in software.
 LRO is not supported.

 4.8) Physical
 The driver is compatible with PAL to work with PHY and GPHY devices.

 4.9) Platform information
 Several driver's information can be passed through the platform
 These are included in the include/linux/stmmac.h header file
 and detailed below as well:

 struct plat_stmmacenet_data {
 	char *phy_bus_name;
 	int bus_id;
 	int phy_addr;
 	int interface;
 	struct stmmac_mdio_bus_data *mdio_bus_data;
 	struct stmmac_dma_cfg *dma_cfg;
 	int clk_csr;
 	int has_gmac;
 	int enh_desc;
 	int tx_coe;
 	int rx_coe;
 	int bugged_jumbo;
 	int pmt;
 	int force_sf_dma_mode;
 	void (*fix_mac_speed)(void *priv, unsigned int speed);
 	void (*bus_setup)(void __iomem *ioaddr);
 	int (*init)(struct platform_device *pdev);
 	void (*exit)(struct platform_device *pdev);
 	void *custom_cfg;
 	void *custom_data;
 	void *bsp_priv;
  };

 Where:
  o phy_bus_name: phy bus name to attach to the stmmac.
  o bus_id: bus identifier.
  o phy_addr: the physical address can be passed from the platform.
 	    If it is set to -1 the driver will automatically
 	    detect it at run-time by probing all the 32 addresses.
  o interface: PHY device's interface.
  o mdio_bus_data: specific platform fields for the MDIO bus.
  o dma_cfg: internal DMA parameters
    o pbl: the Programmable Burst Length is maximum number of beats to
        be transferred in one DMA transaction.
        GMAC also enables the 4xPBL by default.
    o fixed_burst/mixed_burst/burst_len
  o clk_csr: fixed CSR Clock range selection.
  o has_gmac: uses the GMAC core.
  o enh_desc: if sets the MAC will use the enhanced descriptor structure.
  o tx_coe: core is able to perform the tx csum in HW.
  o rx_coe: the supports three check sum offloading engine types:
 	   type_1, type_2 (full csum) and no RX coe.
  o bugged_jumbo: some HWs are not able to perform the csum in HW for
 		over-sized frames due to limited buffer sizes.
 		Setting this flag the csum will be done in SW on
 		JUMBO frames.
  o pmt: core has the embedded power module (optional).
  o force_sf_dma_mode: force DMA to use the Store and Forward mode
 		     instead of the Threshold.
  o fix_mac_speed: this callback is used for modifying some syscfg registers
 		 (on ST SoCs) according to the link speed negotiated by the
 		 physical layer .
  o bus_setup: perform HW setup of the bus. For example, on some ST platforms
 	     this field is used to configure the AMBA  bridge to generate more
 	     efficient STBus traffic.
  o init/exit: callbacks used for calling a custom initialisation;
 	     this is sometime necessary on some platforms (e.g. ST boxes)
 	     where the HW needs to have set some PIO lines or system cfg
 	     registers.
  o custom_cfg/custom_data: this is a custom configuration that can be passed
 			   while initialising the resources.
  o bsp_priv: another private poiter.

 For MDIO bus The we have:

  struct stmmac_mdio_bus_data {
 	int bus_id;
 	int (*phy_reset)(void *priv);
 	unsigned int phy_mask;
 	int *irqs;
 	int probed_phy_irq;
  };

 Where:
  o bus_id: bus identifier;
  o phy_reset: hook to reset the phy device attached to the bus.
  o phy_mask: phy mask passed when register the MDIO bus within the driver.
  o irqs: list of IRQs, one per PHY.
  o probed_phy_irq: if irqs is NULL, use this for probed PHY.

 For DMA engine we have the following internal fields that should be
 tuned according to the HW capabilities.

 struct stmmac_dma_cfg {
 	int pbl;
 	int fixed_burst;
 	int burst_len_supported;
 };

 Where:
  o pbl: Programmable Burst Length
  o fixed_burst: program the DMA to use the fixed burst mode
  o burst_len: this is the value we put in the register
 	      supported values are provided as macros in
 	      linux/stmmac.h header file.

 ---

 Below an example how the structures above are using on ST platforms.

  static struct plat_stmmacenet_data stxYYY_ethernet_platform_data = {
 	.has_gmac = 0,
 	.enh_desc = 0,
 	.fix_mac_speed = stxYYY_ethernet_fix_mac_speed,
 				|
 				|-> to write an internal syscfg
 				|   on this platform when the
 				|   link speed changes from 10 to
 				|   100 and viceversa
 	.init = &stmmac_claim_resource,
 				|
 				|-> On ST SoC this calls own "PAD"
 				|   manager framework to claim
 				|   all the resources necessary
 				|   (GPIO ...). The .custom_cfg field
 				|   is used to pass a custom config.
 };

 Below the usage of the stmmac_mdio_bus_data: on this SoC, in fact,
 there are two MAC cores: one MAC is for MDIO Bus/PHY emulation
 with fixed_link support.

 static struct stmmac_mdio_bus_data stmmac1_mdio_bus = {
 	.bus_id = 1,
 		|
 		|-> phy device on the bus_id 1
 	.phy_reset = phy_reset;
 		|
 		|-> function to provide the phy_reset on this board
 	.phy_mask = 0,
 };

 static struct fixed_phy_status stmmac0_fixed_phy_status = {
 	.link = 1,
 	.speed = 100,
 	.duplex = 1,
 };

 During the board's device_init we can configure the first
 MAC for fixed_link by calling:
   fixed_phy_add(PHY_POLL, 1, &stmmac0_fixed_phy_status));)
 and the second one, with a real PHY device attached to the bus,
 by using the stmmac_mdio_bus_data structure (to provide the id, the
 reset procedure etc).

 4.10) List of source files:
  o Kconfig
  o Makefile
  o stmmac_main.c: main network device driver;
  o stmmac_mdio.c: mdio functions;
  o stmmac_pci: PCI driver;
  o stmmac_platform.c: platform driver
  o stmmac_ethtool.c: ethtool support;
  o stmmac_timer.[ch]: timer code used for mitigating the driver dma interrupts
 		      (only tested on ST40 platforms based);
  o stmmac.h: private driver structure;
  o common.h: common definitions and VFTs;
  o descs.h: descriptor structure definitions;
  o dwmac1000_core.c: GMAC core functions;
  o dwmac1000_dma.c:  dma functions for the GMAC chip;
  o dwmac1000.h: specific header file for the GMAC;
  o dwmac100_core: MAC 100 core and dma code;
  o dwmac100_dma.c: dma funtions for the MAC chip;
  o dwmac1000.h: specific header file for the MAC;
  o dwmac_lib.c: generic DMA functions shared among chips;
  o enh_desc.c: functions for handling enhanced descriptors;
  o norm_desc.c: functions for handling normal descriptors;
  o chain_mode.c/ring_mode.c:: functions to manage RING/CHAINED modes;
  o mmc_core.c/mmc.h: Management MAC Counters;

 5) Debug Information

 The driver exports many information i.e. internal statistics,
 debug information, MAC and DMA registers etc.

 These can be read in several ways depending on the
 type of the information actually needed.

 For example a user can be use the ethtool support
 to get statistics: e.g. using: ethtool -S ethX
 (that shows the Management counters (MMC) if supported)
 or sees the MAC/DMA registers: e.g. using: ethtool -d ethX

 Compiling the Kernel with CONFIG_DEBUG_FS and enabling the
 STMMAC_DEBUG_FS option the driver will export the following
 debugfs entries:

 /sys/kernel/debug/stmmaceth/descriptors_status
   To show the DMA TX/RX descriptor rings

 Developer can also use the "debug" module parameter to get
 further debug information.

 In the end, there are other macros (that cannot be enabled
 via menuconfig) to turn-on the RX/TX DMA debugging,
 specific MAC core debug printk etc. Others to enable the
 debug in the TX and RX processes.
 All these are only useful during the developing stage
 and should never enabled inside the code for general usage.
 In fact, these can generate an huge amount of debug messages.

 6) Energy Efficient Ethernet

 Energy Efficient Ethernet(EEE) enables IEEE 802.3 MAC sublayer along
 with a family of Physical layer to operate in the Low power Idle(LPI)
 mode. The EEE mode supports the IEEE 802.3 MAC operation at 100Mbps,
 1000Mbps & 10Gbps.

 The LPI mode allows power saving by switching off parts of the
 communication device functionality when there is no data to be
 transmitted & received. The system on both the side of the link can
 disable some functionalities & save power during the period of low-link
 utilization. The MAC controls whether the system should enter or exit
 the LPI mode & communicate this to PHY.

 As soon as the interface is opened, the driver verifies if the EEE can
 be supported. This is done by looking at both the DMA HW capability
 register and the PHY devices MCD registers.
 To enter in Tx LPI mode the driver needs to have a software timer
 that enable and disable the LPI mode when there is nothing to be
 transmitted.

 7) TODO:
  o XGMAC is not supported.
  o Add the PTP - precision time protocol
	STMicroelectronics 10/100/1000 Synopsys Ethernet driver

	Copyright (C) 2007-2010 STMicroelectronics Ltd
	Author: Giuseppe Cavallaro <peppe.cavallaro@st.com>

	This is the driver for the MAC 10/100/1000 on-chip Ethernet controllers
	(Synopsys IP blocks).

	Currently this network device driver is for all STM embedded MAC/GMAC
	(i.e. 7xxx/5xxx SoCs), SPEAr (arm), Loongson1B (mips) and XLINX XC2V3000
	FF1152AMT0221 D1215994A VIRTEX FPGA board.

	DWC Ether MAC 10/100/1000 Universal version 3.60a (and older) and DWC Ether
	MAC 10/100 Universal version 4.0 have been used for developing this driver.

	This driver supports both the platform bus and PCI.

	Please, for more information also visit: www.stlinux.com

	1) Kernel Configuration
	The kernel configuration option is STMMAC_ETH:
	Device Drivers ---> Network device support ---> Ethernet (1000 Mbit) --->
	STMicroelectronics 10/100/1000 Ethernet driver (STMMAC_ETH)

	2) Driver parameters list:
	debug: message level (0: no output, 16: all);
	phyaddr: to manually provide the physical address to the PHY device;
	dma_rxsize: DMA rx ring size;
	dma_txsize: DMA tx ring size;
	buf_sz: DMA buffer size;
	tc: control the HW FIFO threshold;
	tx_coe: Enable/Disable Tx Checksum Offload engine;
	watchdog: transmit timeout (in milliseconds);
	flow_ctrl: Flow control ability [on/off];
	pause: Flow Control Pause Time;
	tmrate: timer period (only if timer optimisation is configured).

	3) Command line options
	Driver parameters can be also passed in command line by using:
	stmmaceth=dma_rxsize:128,dma_txsize:512

	4) Driver information and notes

	4.1) Transmit process
	The xmit method is invoked when the kernel needs to transmit a packet; it sets
	the descriptors in the ring and informs the DMA engine that there is a packet
	ready to be transmitted.
	Once the controller has finished transmitting the packet, an interrupt is
	triggered; So the driver will be able to release the socket buffers.
	By default, the driver sets the NETIF_F_SG bit in the features field of the
	net_device structure enabling the scatter/gather feature.

	4.2) Receive process
	When one or more packets are received, an interrupt happens. The interrupts
	are not queued so the driver has to scan all the descriptors in the ring during
	the receive process.
	This is based on NAPI so the interrupt handler signals only if there is work
	to be done, and it exits.
	Then the poll method will be scheduled at some future point.
	The incoming packets are stored, by the DMA, in a list of pre-allocated socket
	buffers in order to avoid the memcpy (Zero-copy).

	4.3) Timer-Driver Interrupt
	Instead of having the device that asynchronously notifies the frame receptions,
	the driver configures a timer to generate an interrupt at regular intervals.
	Based on the granularity of the timer, the frames that are received by the
	device will experience different levels of latency. Some NICs have dedicated
	timer device to perform this task. STMMAC can use either the RTC device or the
	TMU channel 2 on STLinux platforms.
	The timers frequency can be passed to the driver as parameter; when change it,
	take care of both hardware capability and network stability/performance impact.
	Several performance tests on STM platforms showed this optimisation allows to
	spare the CPU while having the maximum throughput.

	4.4) WOL
	Wake up on Lan feature through Magic and Unicast frames are supported for the
	GMAC core.

	4.5) DMA descriptors
	Driver handles both normal and enhanced descriptors. The latter has been only
	tested on DWC Ether MAC 10/100/1000 Universal version 3.41a and later.

	STMMAC supports DMA descriptor to operate both in dual buffer (RING)
	and linked-list(CHAINED) mode. In RING each descriptor points to two
	data buffer pointers whereas in CHAINED mode they point to only one data
	buffer pointer. RING mode is the default.

	In CHAINED mode each descriptor will have pointer to next descriptor in
	the list, hence creating the explicit chaining in the descriptor itself,
	whereas such explicit chaining is not possible in RING mode.

	4.6) Ethtool support
	Ethtool is supported. Driver statistics and internal errors can be taken using:
	ethtool -S ethX command. It is possible to dump registers etc.

	4.7) Jumbo and Segmentation Offloading
	Jumbo frames are supported and tested for the GMAC.
	The GSO has been also added but it's performed in software.
	LRO is not supported.

	4.8) Physical
	The driver is compatible with PAL to work with PHY and GPHY devices.

	4.9) Platform information
	Several driver's information can be passed through the platform
	These are included in the include/linux/stmmac.h header file
	and detailed below as well:

	struct plat_stmmacenet_data {
	char *phy_bus_name;
	int bus_id;
	int phy_addr;
	int interface;
	struct stmmac_mdio_bus_data *mdio_bus_data;
	struct stmmac_dma_cfg *dma_cfg;
	int clk_csr;
	int has_gmac;
	int enh_desc;
	int tx_coe;
	int rx_coe;
	int bugged_jumbo;
	int pmt;
	int force_sf_dma_mode;
	void (fix_mac_speed)(void priv, unsigned int speed);
	void (bus_setup)(void __iomem ioaddr);
	int (init)(struct platform_device pdev);
	void (exit)(struct platform_device pdev);
	void *custom_cfg;
	void *custom_data;
	void *bsp_priv;
	};

	Where:
	o phy_bus_name: phy bus name to attach to the stmmac.
	o bus_id: bus identifier.
	o phy_addr: the physical address can be passed from the platform.
	If it is set to -1 the driver will automatically
	detect it at run-time by probing all the 32 addresses.
	o interface: PHY device's interface.
	o mdio_bus_data: specific platform fields for the MDIO bus.
	o dma_cfg: internal DMA parameters
	o pbl: the Programmable Burst Length is maximum number of beats to
	be transferred in one DMA transaction.
	GMAC also enables the 4xPBL by default.
	o fixed_burst/mixed_burst/burst_len
	o clk_csr: fixed CSR Clock range selection.
	o has_gmac: uses the GMAC core.
	o enh_desc: if sets the MAC will use the enhanced descriptor structure.
	o tx_coe: core is able to perform the tx csum in HW.
	o rx_coe: the supports three check sum offloading engine types:
	type_1, type_2 (full csum) and no RX coe.
	o bugged_jumbo: some HWs are not able to perform the csum in HW for
	over-sized frames due to limited buffer sizes.
	Setting this flag the csum will be done in SW on
	JUMBO frames.
	o pmt: core has the embedded power module (optional).
	o force_sf_dma_mode: force DMA to use the Store and Forward mode
	instead of the Threshold.
	o fix_mac_speed: this callback is used for modifying some syscfg registers
	(on ST SoCs) according to the link speed negotiated by the
	physical layer .
	o bus_setup: perform HW setup of the bus. For example, on some ST platforms
	this field is used to configure the AMBA bridge to generate more
	efficient STBus traffic.
	o init/exit: callbacks used for calling a custom initialisation;
	this is sometime necessary on some platforms (e.g. ST boxes)
	where the HW needs to have set some PIO lines or system cfg
	registers.
	o custom_cfg/custom_data: this is a custom configuration that can be passed
	while initialising the resources.
	o bsp_priv: another private poiter.

	For MDIO bus The we have:

	struct stmmac_mdio_bus_data {
	int bus_id;
	int (phy_reset)(void priv);
	unsigned int phy_mask;
	int *irqs;
	int probed_phy_irq;
	};

	Where:
	o bus_id: bus identifier;
	o phy_reset: hook to reset the phy device attached to the bus.
	o phy_mask: phy mask passed when register the MDIO bus within the driver.
	o irqs: list of IRQs, one per PHY.
	o probed_phy_irq: if irqs is NULL, use this for probed PHY.

	For DMA engine we have the following internal fields that should be
	tuned according to the HW capabilities.

	struct stmmac_dma_cfg {
	int pbl;
	int fixed_burst;
	int burst_len_supported;
	};

	Where:
	o pbl: Programmable Burst Length
	o fixed_burst: program the DMA to use the fixed burst mode
	o burst_len: this is the value we put in the register
	supported values are provided as macros in
	linux/stmmac.h header file.

	---

	Below an example how the structures above are using on ST platforms.

	static struct plat_stmmacenet_data stxYYY_ethernet_platform_data = {
	.has_gmac = 0,
	.enh_desc = 0,
	.fix_mac_speed = stxYYY_ethernet_fix_mac_speed,
	\|
	\|-> to write an internal syscfg
	\| on this platform when the
	\| link speed changes from 10 to
	\| 100 and viceversa
	.init = &stmmac_claim_resource,
	\|
	\|-> On ST SoC this calls own "PAD"
	\| manager framework to claim
	\| all the resources necessary
	\| (GPIO ...). The .custom_cfg field
	\| is used to pass a custom config.
	};

	Below the usage of the stmmac_mdio_bus_data: on this SoC, in fact,
	there are two MAC cores: one MAC is for MDIO Bus/PHY emulation
	with fixed_link support.

	static struct stmmac_mdio_bus_data stmmac1_mdio_bus = {
	.bus_id = 1,
	\|
	\|-> phy device on the bus_id 1
	.phy_reset = phy_reset;
	\|
	\|-> function to provide the phy_reset on this board
	.phy_mask = 0,
	};

	static struct fixed_phy_status stmmac0_fixed_phy_status = {
	.link = 1,
	.speed = 100,
	.duplex = 1,
	};

	During the board's device_init we can configure the first
	MAC for fixed_link by calling:
	fixed_phy_add(PHY_POLL, 1, &stmmac0_fixed_phy_status));)
	and the second one, with a real PHY device attached to the bus,
	by using the stmmac_mdio_bus_data structure (to provide the id, the
	reset procedure etc).

	4.10) List of source files:
	o Kconfig
	o Makefile
	o stmmac_main.c: main network device driver;
	o stmmac_mdio.c: mdio functions;
	o stmmac_pci: PCI driver;
	o stmmac_platform.c: platform driver
	o stmmac_ethtool.c: ethtool support;
	o stmmac_timer.[ch]: timer code used for mitigating the driver dma interrupts
	(only tested on ST40 platforms based);
	o stmmac.h: private driver structure;
	o common.h: common definitions and VFTs;
	o descs.h: descriptor structure definitions;
	o dwmac1000_core.c: GMAC core functions;
	o dwmac1000_dma.c: dma functions for the GMAC chip;
	o dwmac1000.h: specific header file for the GMAC;
	o dwmac100_core: MAC 100 core and dma code;
	o dwmac100_dma.c: dma funtions for the MAC chip;
	o dwmac1000.h: specific header file for the MAC;
	o dwmac_lib.c: generic DMA functions shared among chips;
	o enh_desc.c: functions for handling enhanced descriptors;
	o norm_desc.c: functions for handling normal descriptors;
	o chain_mode.c/ring_mode.c:: functions to manage RING/CHAINED modes;
	o mmc_core.c/mmc.h: Management MAC Counters;

	5) Debug Information

	The driver exports many information i.e. internal statistics,
	debug information, MAC and DMA registers etc.

	These can be read in several ways depending on the
	type of the information actually needed.

	For example a user can be use the ethtool support
	to get statistics: e.g. using: ethtool -S ethX
	(that shows the Management counters (MMC) if supported)
	or sees the MAC/DMA registers: e.g. using: ethtool -d ethX

	Compiling the Kernel with CONFIG_DEBUG_FS and enabling the
	STMMAC_DEBUG_FS option the driver will export the following
	debugfs entries:

	/sys/kernel/debug/stmmaceth/descriptors_status
	To show the DMA TX/RX descriptor rings

	Developer can also use the "debug" module parameter to get
	further debug information.

	In the end, there are other macros (that cannot be enabled
	via menuconfig) to turn-on the RX/TX DMA debugging,
	specific MAC core debug printk etc. Others to enable the
	debug in the TX and RX processes.
	All these are only useful during the developing stage
	and should never enabled inside the code for general usage.
	In fact, these can generate an huge amount of debug messages.

	6) Energy Efficient Ethernet

	Energy Efficient Ethernet(EEE) enables IEEE 802.3 MAC sublayer along
	with a family of Physical layer to operate in the Low power Idle(LPI)
	mode. The EEE mode supports the IEEE 802.3 MAC operation at 100Mbps,
	1000Mbps & 10Gbps.

	The LPI mode allows power saving by switching off parts of the
	communication device functionality when there is no data to be
	transmitted & received. The system on both the side of the link can
	disable some functionalities & save power during the period of low-link
	utilization. The MAC controls whether the system should enter or exit
	the LPI mode & communicate this to PHY.

	As soon as the interface is opened, the driver verifies if the EEE can
	be supported. This is done by looking at both the DMA HW capability
	register and the PHY devices MCD registers.
	To enter in Tx LPI mode the driver needs to have a software timer
	that enable and disable the LPI mode when there is nothing to be
	transmitted.

	7) TODO:
	o XGMAC is not supported.
	o Add the PTP - precision time protocol