Am Freitag, den 10.04.2015, 03:01 +0200 schrieb Sebastian Hesselbarth:
> Commit a76c62f80d95860e6c5904ab5cb91667c43f61eb
> ("net: mvneta: convert to streaming DMA ops")
> converted explicit ARM cache flushes to streaming DMA calls.
>
> However, in mvneta_send() we are not interested in the sent data buffer
> anymore. Also, in mvneta_recv() the device does not care about received
> data buffer.
>
> Remove unnecessary dma_sync_single_for_cpu() in mvneta_send() and
> dma_sync_single_for_device() in mvneta_recv().
>
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@xxxxxxxxx>
NACK: see below.
> ---
> Cc: barebox@xxxxxxxxxxxxxxxxxxx
> Cc: Lucas Stach <dev@xxxxxxxxxx>
> Cc: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxxxxxxxxxx>
> Cc: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/net/mvneta.c | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/drivers/net/mvneta.c b/drivers/net/mvneta.c
> index 3be2ec531fb1..e1c7f15210e4 100644
> --- a/drivers/net/mvneta.c
> +++ b/drivers/net/mvneta.c
> @@ -409,7 +409,6 @@ static int mvneta_send(struct eth_device *edev, void *data, int len)
> * the Tx port status register (PTXS).
> */
> ret = wait_on_timeout(TRANSFER_TIMEOUT, !mvneta_pending_tx(priv));
> - dma_sync_single_for_cpu((unsigned long)data, len, DMA_TO_DEVICE);
This makes sure the CPU has a consistent view of memory. If something
got speculatively loaded into the cache you will write out invalid data
on the next send.
> if (ret) {
> dev_err(&edev->dev, "transmit timeout\n");
> return ret;
> @@ -468,9 +467,6 @@ static int mvneta_recv(struct eth_device *edev)
> rxdesc->data_size - MVNETA_MH_SIZE);
> ret = 0;
>
> - dma_sync_single_for_device((unsigned long)rxdesc->buf_phys_addr,
> - ALIGN(PKTSIZE, 8), DMA_FROM_DEVICE);
> -
The buffer is reused for the next receive operation. This isn't syncing
the data to the device, but is actually a cache invalidate to make sure
there is no pending cache writeback that may corrupt your received data.
> recv_err:
> /* reset this and get next rx descriptor*/
> rxdesc->data_size = 0;
The DMA API has a notion of buffer ownership. Accessing a buffer without
transferring the ownership to the appropriate entity (cpu or device) is
illegal. Using the DMA API in a non balanced manner is skipping the
ownership transfer.
Regards,
Lucas
_______________________________________________
barebox mailing list
barebox@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/barebox
