i2c: designware: make SCL and SDA falling time configurable
This patch allows to set independantly SCL and SDA falling times.
The tLOW period is computed by taking into account the SCL falling time.
The tHIGH period is computed by taking into account the SDA falling time.
For instance in case the margin on tLOW is considered too small, it can
be increased by increasing the SCL falling time which is by default set
at 300ns.
The same applies for tHIGH period with the help of SDA falling time.
Signed-off-by: Romain Baeriswyl <romainba@abilis.com>
Reviewed-by: Christian Ruppert <christian.ruppert@abilis.com>
Acked-by: Shinya Kuribayashi <skuribay@pobox.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 14c4b30..22e92c3 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -218,7 +218,7 @@
*
* If your hardware is free from tHD;STA issue, try this one.
*/
- return (ic_clk * tSYMBOL + 5000) / 10000 - 8 + offset;
+ return (ic_clk * tSYMBOL + 500000) / 1000000 - 8 + offset;
else
/*
* Conditional expression:
@@ -234,7 +234,8 @@
* The reason why we need to take into account "tf" here,
* is the same as described in i2c_dw_scl_lcnt().
*/
- return (ic_clk * (tSYMBOL + tf) + 5000) / 10000 - 3 + offset;
+ return (ic_clk * (tSYMBOL + tf) + 500000) / 1000000
+ - 3 + offset;
}
static u32 i2c_dw_scl_lcnt(u32 ic_clk, u32 tLOW, u32 tf, int offset)
@@ -250,7 +251,7 @@
* account the fall time of SCL signal (tf). Default tf value
* should be 0.3 us, for safety.
*/
- return ((ic_clk * (tLOW + tf) + 5000) / 10000) - 1 + offset;
+ return ((ic_clk * (tLOW + tf) + 500000) / 1000000) - 1 + offset;
}
static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
@@ -287,6 +288,7 @@
u32 input_clock_khz;
u32 hcnt, lcnt;
u32 reg;
+ u32 sda_falling_time, scl_falling_time;
input_clock_khz = dev->get_clk_rate_khz(dev);
@@ -308,15 +310,18 @@
/* set standard and fast speed deviders for high/low periods */
+ sda_falling_time = dev->sda_falling_time ?: 300; /* ns */
+ scl_falling_time = dev->scl_falling_time ?: 300; /* ns */
+
/* Standard-mode */
hcnt = i2c_dw_scl_hcnt(input_clock_khz,
- 40, /* tHD;STA = tHIGH = 4.0 us */
- 3, /* tf = 0.3 us */
+ 4000, /* tHD;STA = tHIGH = 4.0 us */
+ sda_falling_time,
0, /* 0: DW default, 1: Ideal */
0); /* No offset */
lcnt = i2c_dw_scl_lcnt(input_clock_khz,
- 47, /* tLOW = 4.7 us */
- 3, /* tf = 0.3 us */
+ 4700, /* tLOW = 4.7 us */
+ scl_falling_time,
0); /* No offset */
/* Allow platforms to specify the ideal HCNT and LCNT values */
@@ -330,13 +335,13 @@
/* Fast-mode */
hcnt = i2c_dw_scl_hcnt(input_clock_khz,
- 6, /* tHD;STA = tHIGH = 0.6 us */
- 3, /* tf = 0.3 us */
+ 600, /* tHD;STA = tHIGH = 0.6 us */
+ sda_falling_time,
0, /* 0: DW default, 1: Ideal */
0); /* No offset */
lcnt = i2c_dw_scl_lcnt(input_clock_khz,
- 13, /* tLOW = 1.3 us */
- 3, /* tf = 0.3 us */
+ 1300, /* tLOW = 1.3 us */
+ scl_falling_time,
0); /* No offset */
if (dev->fs_hcnt && dev->fs_lcnt) {