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-iso.c b/drivers/firewire/fw-iso.c
index 3ff2cfc1bba648dbb22d2962b2fc6aec07483cfe..39f3bacee4047a2e979e2988150536f2537b2b31 100644 (file)
--- a/drivers/firewire/fw-iso.c
+++ b/drivers/firewire/fw-iso.c
@@ -110,7 +110,8 @@ struct fw_iso_context *fw_iso_context_create(struct fw_card *card,
 {
        struct fw_iso_context *ctx;
 
-       ctx = card->driver->allocate_iso_context(card, type, header_size);
+       ctx = card->driver->allocate_iso_context(card,
+                                                type, channel, header_size);
        if (IS_ERR(ctx))
                return ctx;
 

diff --git a/drivers/firewire/fw-ohci.c b/drivers/firewire/fw-ohci.c
index 4c7cf15986aecbccbbfd4184eece3de7c5b405b2..859af71b06a800d4261d40f2a060f263753d98ee 100644 (file)
--- a/drivers/firewire/fw-ohci.c
+++ b/drivers/firewire/fw-ohci.c
@@ -205,6 +205,7 @@ struct fw_ohci {
 
        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 int handle_it_packet(struct context *context,
 }
 
 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 @@ static struct fw_iso_context *ohci_allocate_iso_context(struct fw_card *card,
        }
 
        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 @@ static void ohci_free_iso_context(struct fw_iso_context *base)
        } 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 @@ static int __devinit pci_probe(struct pci_dev *dev,
        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);

diff --git a/drivers/firewire/fw-transaction.h b/drivers/firewire/fw-transaction.h
index 0dd96ecc2dcd2d25dd7dd1673a6b5082006a460c..48e88d53998b07cb0a949bd1b12c2b8fbde3b813 100644 (file)
--- a/drivers/firewire/fw-transaction.h
+++ b/drivers/firewire/fw-transaction.h
@@ -383,7 +383,7 @@ struct fw_card_driver {
 
        struct fw_iso_context *
        (*allocate_iso_context)(struct fw_card *card,
-                               int type, size_t header_size);
+                               int type, int channel, size_t header_size);
        void (*free_iso_context)(struct fw_iso_context *ctx);
 
        int (*start_iso)(struct fw_iso_context *ctx,