Merge tag 'firewire-updates' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394

Pull firewire updates from Stefan Richter

  - make JMicron JMB38x controllers work with IOMMU-equipped systems

  - IP-over-1394: allow user-configured MTU of up to 4096 bytes

* tag 'firewire-updates' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394:
  firewire-ohci: work around oversized DMA reads on JMicron controllers
  firewire: net: max MTU off by one

2 files changed, 13 insertions, 2 deletions

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 242359c..60e75e6 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -1480,9 +1480,14 @@ static int fwnet_probe(struct fw_unit *unit,
 		goto out;
 	dev->local_fifo = dev->handler.offset;
 
+	/*
+	 * default MTU: RFC 2734 cl. 4, RFC 3146 cl. 4
+	 * maximum MTU: RFC 2734 cl. 4.2, fragment encapsulation header's
+	 *              maximum possible datagram_size + 1 = 0xfff + 1
+	 */
 	net->mtu = 1500U;
 	net->min_mtu = ETH_MIN_MTU;
-	net->max_mtu = 0xfff;
+	net->max_mtu = 4096U;
 
 	/* Set our hardware address while we're at it */
 	ha = (union fwnet_hwaddr *)net->dev_addr;
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index ccf5236..45c0487 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -1128,7 +1128,13 @@ static int context_add_buffer(struct context *ctx)
 		return -ENOMEM;
 
 	offset = (void *)&desc->buffer - (void *)desc;
-	desc->buffer_size = PAGE_SIZE - offset;
+	/*
+	 * Some controllers, like JMicron ones, always issue 0x20-byte DMA reads
+	 * for descriptors, even 0x10-byte ones. This can cause page faults when
+	 * an IOMMU is in use and the oversized read crosses a page boundary.
+	 * Work around this by always leaving at least 0x10 bytes of padding.
+	 */
+	desc->buffer_size = PAGE_SIZE - offset - 0x10;
 	desc->buffer_bus = bus_addr + offset;
 	desc->used = 0;