Re: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus address in tbnet_tx_callback()

On Sat, Nov 11, 2017 at 07:21:24PM +0900, David Miller wrote:

From: Mika Westerberg <mika.westerberg@linux.intel.com>
Date: Thu,  9 Nov 2017 13:46:28 +0300

quoted

When Thunderbolt network interface is disabled or when the cable is
unplugged the driver releases all allocated buffers by calling
tbnet_free_buffers() for each ring. This function then calls
dma_unmap_page() for each buffer it finds where bus address is non-zero.
Now, we only clear this bus address when the Tx buffer is sent to the
hardware so it is possible that the function finds an entry that has
already been unmapped.

Enabling DMA-API debugging catches this as well:

  thunderbolt 0000:06:00.0: DMA-API: device driver tries to free DMA
    memory it has not allocated [device address=0x0000000068321000] [size=4096 bytes]

Fix this by clearing the bus address of a Tx frame right after we have
unmapped the buffer.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Applied, but assuming zero is a non-valid DMA address is never a good
idea.  That's why we have the DMA error code signaling abstracted.

There does not seem to be a way to mark DMA address invalid in a driver
so we probably need to add a flag to struct tbnet_frame instead.