netdev - Re: [PATCH] net: mvpp2: avoid bouncing buffers

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Message-ID: <20180820062326.GA22222@infradead.org>
Date:   Sun, 19 Aug 2018 23:23:26 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     David Miller <davem@...emloft.net>
Cc:     brian.brooks@...aro.org, antoine.tenart@...tlin.com,
        maxime.chevallier@...tlin.com, ymarkman@...vell.com,
        stefanc@...vell.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bjorn.topel@...el.com,
        brian.brooks@....com
Subject: Re: [PATCH] net: mvpp2: avoid bouncing buffers

On Sun, Aug 19, 2018 at 07:55:05PM -0700, David Miller wrote:
> From: Brian Brooks <brian.brooks@...aro.org>
> Date: Sun, 19 Aug 2018 21:47:30 -0500
> 
> > @@ -5126,6 +5126,12 @@ static int mvpp2_probe(struct platform_device *pdev)
> >  	}
> >  
> >  	if (priv->hw_version == MVPP22) {
> > +		/* Platform code may have set dev->dma_mask to point
> > +		 * to dev->coherent_dma_mask, but we want to ensure
> > +		 * they take different values due to comment below.
> > +		 */
> > +		pdev->dev.dma_mask = &priv->dma_mask;
> 
> The platform code might be doing this exactly because it cannot support
> different coherent and streaming DMA masks.
> 
> Well, in any case, the platform code is doing it for a reason and
> overriding this in a "driver" of all places seems totally
> inappropriate and at best a layering violation.
> 
> I would rather you fix this in a way that involves well defined APIs
> that set the DMA masks or whatever to the values that you need, rather
> than going behind the platform code's back and changing the DMA mask
> pointer like this.

Agreed.  What platform do you see this issue on?