netdev - Re: [PATCH v2 net-next 12/15] net: ethernet: mtk_eth_soc: introduce MTK_NETSYS

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Message-ID: <20220518084740.7947b51b@kernel.org>
Date:   Wed, 18 May 2022 08:47:40 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, nbd@....name, john@...ozen.org,
        sean.wang@...iatek.com, Mark-MC.Lee@...iatek.com,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        Sam.Shih@...iatek.com, linux-mediatek@...ts.infradead.org,
        devicetree@...r.kernel.org, robh@...nel.org,
        lorenzo.bianconi@...hat.com
Subject: Re: [PATCH v2 net-next 12/15] net: ethernet: mtk_eth_soc: introduce
 MTK_NETSYS_V2 support

On Wed, 18 May 2022 11:53:12 +0200 Lorenzo Bianconi wrote:
> > > +	WRITE_ONCE(desc->txd7, 0);
> > > +	WRITE_ONCE(desc->txd8, 0);  
> > 
> > Why all the WRITE_ONCE()? Don't you just need a barrier between writing
> > the descriptor and kicking the HW?   
> 
> I used this approach just to be aligned with current codebase:
> https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/mediatek/mtk_eth_soc.c#L1006
> https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/mediatek/mtk_eth_soc.c#L1031
> 
> but I guess we can even convert the code to use barrier instead. Agree?

Oh, I didn't realize. No preference on converting the old code 
but it looks like a cargo cult to me so in the new code let's 
not WRITE_ONCE() all descriptor writes unless there's a reason.