linux-kernel - Re: use generic DMA mapping code in powerpc V4

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Date:   Wed, 28 Nov 2018 21:35:10 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     Christian Zigotzky <chzigotzky@...osoft.de>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: use generic DMA mapping code in powerpc V4

On Wed, 28 Nov 2018 16:55:30 +0100
Christian Zigotzky <chzigotzky@...osoft.de> wrote:

> On 28 November 2018 at 12:05PM, Michael Ellerman wrote:
> > Nothing specific yet.
> >
> > I'm a bit worried it might break one of the many old obscure platforms
> > we have that aren't well tested.
> >  
> Please don't apply the new DMA mapping code if you don't be sure if it 
> works on all supported PowerPC machines. Is the new DMA mapping code 
> really necessary? It's not really nice, to rewrote code if the old code 
> works perfect. We must not forget, that we work for the end users. Does 
> the end user have advantages with this new code? Is it faster? The old 
> code works without any problems. 

There is another service provided to the users as well: new code that is
cleaner and simpler which allows easier bug fixes and new features.
Without being familiar with the DMA mapping code I cannot really say if
that's the case here.

> I am also worried about this code. How 
> can I test this new DMA mapping code?

I suppose if your machine works it works for you.

Thanks

Michal