Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

[Francois Romieu]

Pavel Machek <pavel@xxxxxx> :
[...]
> Considering the memory barriers... is something like this neccessary
> in the via-rhine ?

Yes.

> AFAICT... we need a barrier after making sure that descriptor is no
> longer owned by DMA (to make sure we don't get stale data in rest of
> descriptor)... and we need a barrier before giving the descriptor to
> the dma, to make sure DMA engine sees the complete update....?

I would not expect stale data while processing a single transmit
descriptor as the transmit completion does not use the rest of the
descriptor at all in the via-rhine driver. However I agree that transmit
descriptors should be read by the cpu with adequate ordering so the
dma_rmb() should stay.

Same kind of narrative for dma_wmb rhine_rx (s/read/written/ and
s/cpu/device/).

> diff --git a/drivers/net/ethernet/via/via-rhine.c b/drivers/net/ethernet/via/via-rhine.c
> index ba5c542..3806e72 100644
> --- a/drivers/net/ethernet/via/via-rhine.c
> +++ b/drivers/net/ethernet/via/via-rhine.c
[...]
> @@ -2061,6 +2062,7 @@ static int rhine_rx(struct net_device *dev, int limit)
>  
>  		if (desc_status & DescOwn)
>  			break;
> +		dma_rmb();
>  

I agree with your explanation for this one (late vlan processing in a 
different word from the same descriptor).

-- 
Ueimor