RE: [PATCH] dmaengine: xilinx_dma: Add missing check for empty list

[Radhey Shyam Pandey <radheys@xilinx.com>]

> -----Original Message-----
> From: Sebastian von Ohr <vonohr@smaract.com>
> Sent: Wednesday, April 8, 2020 8:49 PM
> To: Radhey Shyam Pandey <radheys@xilinx.com>; vkoul@kernel.org;
> Appana Durga Kedareswara Rao <appanad@xilinx.com>; Michal Simek
> <michals@xilinx.com>
> Cc: dmaengine@vger.kernel.org
> Subject: RE: [PATCH] dmaengine: xilinx_dma: Add missing check for empty
> list
> 
> I've attached a patch below. When using this patch with the xilinx-
> v2019.2.01
> tag I get a kernel panic immediately when loading the module. Maybe the
> exact
> components on the FPGA are also important. I have one AXI DMA
> component with
> scatter/gather enabled, read/write widths set to 64bit and a max burst size
> of 16.
> 
> 
> diff --git a/drivers/dma/xilinx/axidmatest.c
> b/drivers/dma/xilinx/axidmatest.c
> index 3d88982c9f7e..757bab152e0a 100644
> --- a/drivers/dma/xilinx/axidmatest.c
> +++ b/drivers/dma/xilinx/axidmatest.c
> @@ -407,6 +407,7 @@ static int dmatest_slave_func(void *data)
>  		dma_async_issue_pending(tx_chan);
>  		dma_async_issue_pending(rx_chan);
> 
> +		dma_sync_wait(tx_chan, tx_cookie);
>  		tx_tmo = wait_for_completion_timeout(&tx_cmp, tx_tmo);
> 
>  		status = dma_async_is_tx_complete(tx_chan, tx_cookie,
> @@ -428,6 +429,7 @@ static int dmatest_slave_func(void *data)
>  			continue;
>  		}
> 
> +		dma_sync_wait(rx_chan, rx_cookie);
>  		rx_tmo = wait_for_completion_timeout(&rx_cmp, rx_tmo);
>  		status = dma_async_is_tx_complete(rx_chan, rx_cookie,
>  							NULL, NULL);

Still, the issue is not reproduced, but as you also mentioned it might depend 
on design, exact timing on events, etc.  The patch checks active list empty state
before accessing it so that looks correct. In my test,  it doesn't break any of 
the existing functionality so adding a tested-by tag. 

Tested-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>