linux-kernel - Re: [PATCH 21/22] mmc: wbsd: Use dma_alloc

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Date:   Tue, 22 Feb 2022 09:45:30 +0100
From:   Christoph Hellwig <hch@....de>
To:     Baoquan He <bhe@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, cl@...ux.com,
        42.hyeyoo@...il.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, vbabka@...e.cz, David.Laight@...lab.com,
        david@...hat.com, herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, steffen.klassert@...unet.com,
        netdev@...r.kernel.org, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, linux-s390@...r.kernel.org, michael@...le.cc,
        linux-i2c@...r.kernel.org, wsa@...nel.org
Subject: Re: [PATCH 21/22] mmc: wbsd: Use dma_alloc_noncoherent() for dma
 buffer

On Sun, Feb 20, 2022 at 04:40:44PM +0800, Baoquan He wrote:
> On 02/19/22 at 08:17am, Christoph Hellwig wrote:
> > On Sat, Feb 19, 2022 at 08:52:20AM +0800, Baoquan He wrote:
> > >  	if (request_dma(dma, DRIVER_NAME))
> > >  		goto err;
> > >  
> > > +	dma_set_mask_and_coherent(mmc_dev(host->mmc), DMA_BIT_MASK(24));
> > 
> > This also sets the streaming mask, but the driver doesn't seem to make
> > use of that.  Please document it in the commit log.
> 
> Thanks for reviewing. I will change it to dma_set_mask(), and describe
> this change in patch log.

No, if you change it, it should be dma_set_coherent_mask only as it is
not using streaming mappings.  I suspect dma_set_mask_and_coherent is
the right thing if the driver ever wants to use streaming mapping,
it would just need to be documented in the commit message.