linux-kernel - Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when CONFIG_HAS

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Message-ID: <CAPDyKFqDKUG3RC241hv535CLFGEQc4b-vv0e3bexzGkDSY82Jg@mail.gmail.com>
Date:   Wed, 2 Sep 2020 10:31:47 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Christoph Hellwig <hch@....de>, Rich Felker <dalias@...c.org>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when
 CONFIG_HAS_DMA is unset

On Tue, 1 Sep 2020 at 17:40, Christoph Hellwig <hch@....de> wrote:
>
> On Tue, Sep 01, 2020 at 05:36:17PM +0200, Ulf Hansson wrote:
> > > I still don't think this makes sense, as the dma_mask should always
> > > be non-NULL here.
> >
> > If that is the case, I wonder how the driver could even have worked without DMA.
> >
> > Because in the existing code, host->dma_dev gets assigned to
> > spi->master->dev.parent->dma_mask - which seems to turn on the DMA
> > usage in the driver.
> >
> > What am I missing?
>
> Do you know of other non-DMA users?  For SH nommu it probably worked

I don't know of other non-DMA users. As I said, I wish someone could
step in and take better care of mmc_spi - as I know it's being used a
lot.

> because SH nommu used to provide a DMA implementation that worked
> fine for streaming maps, but was completely broken for coherent
> allocation.  And this driver appears to only use the former.

Alright, so you are saying the DMA support may potentially never have
been optional to this driver. In any case, I can remove the check in
$subject patch, as it shouldn't matter.

Anyway, let's see what Rich thinks of this. I am curious to see if the
patch works on his SH boards - as I haven't been able to test it.

Kind regards
Uffe