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

From	Francois Romieu <romieu@fr.zoreil.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock
Date	2016-12-20 01:10 +0100
Message-ID	<sQgae-6pr-7@gated-at.bofh.it> (permalink)
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Pavel Machek <pavel@ucw.cz> :
[...]
> 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

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Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-11 21:20 +0100
  Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 20:30 +0100
    Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-15 22:20 +0100
      Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 22:40 +0100
        Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 23:40 +0100
          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-17 18:40 +0100
            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-18 01:20 +0100
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-18 17:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 18:30 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 19:40 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-19 23:50 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 21:20 +0100
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-19 11:10 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-20 01:10 +0100

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