firewire: prevent creation of multiple IR DMA contexts for the same channel
OHCI-1394 1.1 clause 10.4.3 says: "If more than one IR DMA context
specifies receives for packets from the same isochronous channel, the
context destination for that channel's packets is undefined."
Any userspace client and in the future also kernelspace clients can
allocate IR DMA contexts for any channel. We don't want them to
interfere with each other, hence it is preferable to return -EBUSY if
allocation of a second context for a channel is attempted.
Notes:
- This limitation is OHCI-1394 specific, therefore its proper place of
implementation is down in the low-level driver.
- Since the <linux/firewire-cdev.h> ABI simply maps one userspace iso
client context to one hardware iso context, this OHCI-1394
limitation alas requires userspace to implement its own multiplexing
of iso reception from the same channel and card to multiple clients
when needed.
- The limitation is independent of channel allocation at the IRM; the
latter is really only important for the initiation of iso
transmission but not of iso reception.
- We don't need to do the same for IT DMA because OHCI-1394 does not
have any ties between IT contexts and channels. Only the voluntary
channel allocation protocol via the IRM, globally to the FireWire
bus, can ensure proper isochronous transmit behaviour anyway.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/fw-ohci.c b/drivers/firewire/fw-ohci.c
index 4c7cf15..859af71 100644
--- a/drivers/firewire/fw-ohci.c
+++ b/drivers/firewire/fw-ohci.c
@@ -205,6 +205,7 @@
u32 it_context_mask;
struct iso_context *it_context_list;
+ u64 ir_context_channels;
u32 ir_context_mask;
struct iso_context *ir_context_list;
};
@@ -1877,20 +1878,23 @@
}
static struct fw_iso_context *ohci_allocate_iso_context(struct fw_card *card,
- int type, size_t header_size)
+ int type, int channel, size_t header_size)
{
struct fw_ohci *ohci = fw_ohci(card);
struct iso_context *ctx, *list;
descriptor_callback_t callback;
+ u64 *channels, dont_care = ~0ULL;
u32 *mask, regs;
unsigned long flags;
int index, ret = -ENOMEM;
if (type == FW_ISO_CONTEXT_TRANSMIT) {
+ channels = &dont_care;
mask = &ohci->it_context_mask;
list = ohci->it_context_list;
callback = handle_it_packet;
} else {
+ channels = &ohci->ir_context_channels;
mask = &ohci->ir_context_mask;
list = ohci->ir_context_list;
if (ohci->use_dualbuffer)
@@ -1900,9 +1904,11 @@
}
spin_lock_irqsave(&ohci->lock, flags);
- index = ffs(*mask) - 1;
- if (index >= 0)
+ index = *channels & 1ULL << channel ? ffs(*mask) - 1 : -1;
+ if (index >= 0) {
+ *channels &= ~(1ULL << channel);
*mask &= ~(1 << index);
+ }
spin_unlock_irqrestore(&ohci->lock, flags);
if (index < 0)
@@ -2012,6 +2018,7 @@
} else {
index = ctx - ohci->ir_context_list;
ohci->ir_context_mask |= 1 << index;
+ ohci->ir_context_channels |= 1ULL << base->channel;
}
spin_unlock_irqrestore(&ohci->lock, flags);
@@ -2424,6 +2431,7 @@
ohci->it_context_list = kzalloc(size, GFP_KERNEL);
reg_write(ohci, OHCI1394_IsoXmitIntMaskSet, ~0);
+ ohci->ir_context_channels = ~0ULL;
ohci->ir_context_mask = reg_read(ohci, OHCI1394_IsoXmitIntMaskSet);
reg_write(ohci, OHCI1394_IsoXmitIntMaskClear, ~0);
size = sizeof(struct iso_context) * hweight32(ohci->ir_context_mask);