RE: [PATCH net-next v2 2/5] lan743x: sync only the received area of an rx ring buffer

[Bryan.Whitehead]

 
> Will do. Are you planning to hold off your tests until v3? It shouldn't take 
> too
> long.

Sure, we will wait for v3

Re: [PATCH net-next v2 2/5] lan743x: sync only the received area of an rx ring buffer

[Sven Van Asbroeck]

Hi Bryan,

On Fri, Feb 12, 2021 at 3:45 PM  wrote:
>
> According to the document I have, FRAME_LENGTH is only valid when LS bit is 
> set, and reserved otherwise.
> Therefore, I'm not sure you can rely on it being zero when LS is not set, 
> even if your experiments say it is.
> Future chip revisions might use those bits differently.

That's good to know. I didn't find any documentation related to
multi-buffer frames, so I had to go with what I saw the chip do
experimentally. It's great that you were able to double-check against
the official docs.

>
> Can you change this so the LS bit is checked.
> If set you can use the smaller of FRAME_LENGTH or buffer length.
> If clear you can just use buffer length.

Will do. Are you planning to hold off your tests until v3? It
shouldn't take too long.

RE: [PATCH net-next v2 2/5] lan743x: sync only the received area of an rx ring buffer

[Bryan.Whitehead]

Hi Sven, see below.

> +   if (buffer_info->dma_ptr) {
> +   /* unmap from dma */
> +   packet_length = RX_DESC_DATA0_FRAME_LENGTH_GET_
> +   (le32_to_cpu(descriptor->data0));
> +   if (packet_length == 0 ||
> +   packet_length > buffer_info->buffer_length)
> +   /* buffer is part of multi-buffer packet: fully used 
> */
> +   packet_length = buffer_info->buffer_length;

According to the document I have, FRAME_LENGTH is only valid when LS bit is 
set, and reserved otherwise.
Therefore, I'm not sure you can rely on it being zero when LS is not set, even 
if your experiments say it is.
Future chip revisions might use those bits differently.

Can you change this so the LS bit is checked.
If set you can use the smaller of FRAME_LENGTH or buffer length.
If clear you can just use buffer length. 

> +   /* sync used part of buffer only */
> +   dma_sync_single_for_cpu(dev, buffer_info->dma_ptr,
> +   packet_length,
> +   DMA_FROM_DEVICE);
> +   dma_unmap_single_attrs(dev, buffer_info->dma_ptr,
> +  buffer_info->buffer_length,
> +  DMA_FROM_DEVICE,
> +  DMA_ATTR_SKIP_CPU_SYNC);
> +   }