Re: [PATCH 1/2] net: macb: fix dma_alloc for rx_buffer

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Steffen,

On 28.11.23 17:29, Steffen Trumtrar wrote:
> rx_buffer gets dma_alloc'ed but is never dma_map'ed and therefor not
> flushed before it is initially used.
> 
> Map the rx_buffer when the macb is initialized and unmap it on ether_halt.
> 
> While at it, cleanup the dma_alloc_coherent rx_ring/tx_ring, too.
> 
> Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> ---
>  drivers/net/macb.c | 37 ++++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/macb.c b/drivers/net/macb.c
> index 260c1e806a..92f78f7253 100644
> --- a/drivers/net/macb.c
> +++ b/drivers/net/macb.c
> @@ -63,10 +63,13 @@ struct macb_device {
>  	unsigned int		tx_head;
>  
>  	void			*rx_buffer;
> +	dma_addr_t		rx_buffer_phys;
>  	void			*tx_buffer;
>  	void			*rx_packet_buf;
>  	struct macb_dma_desc	*rx_ring;
> +	dma_addr_t		rx_ring_phys;
>  	struct macb_dma_desc	*tx_ring;
> +	dma_addr_t		tx_ring_phys;
>  	struct macb_dma_desc	*gem_q1_descs;
>  
>  	int			rx_buffer_size;
> @@ -181,7 +184,7 @@ static int gem_recv(struct eth_device *edev)
>  		barrier();
>  		status = macb->rx_ring[macb->rx_tail].ctrl;
>  		length = MACB_BFEXT(RX_FRMLEN, status);
> -		buffer = macb->rx_buffer + macb->rx_buffer_size * macb->rx_tail;
> +		buffer = (void *)macb->rx_buffer_phys + macb->rx_buffer_size * macb->rx_tail;

For GEM-type NICs, rx_buffer_size is PKTSIZE (1518 bytes currently), which is not a multiple
of the cache line size of the 64 bytes cache line on the ZynqMP's Cortex-A53 the driver
is supposed to support.

>  		dma_sync_single_for_cpu(macb->dev, (unsigned long)buffer, length,
>  					DMA_FROM_DEVICE);

This means this could potentially invalidate adjacent buffer contents.


>  	}
> @@ -891,8 +908,8 @@ static int macb_probe(struct device *dev)
>  
>  	macb_init_rx_buffer_size(macb, PKTSIZE);

^ Here's where PKTSIZE comes from. I'd be in favor of changing the global PKTSIZE
definition to be a multiple of 64 bytes (or use DMA_ALIGNMENT, but this isn't
correctly set for ARM yet.  I just sent out a patch for that).

Cheers,
Ahmad

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