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

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Message-ID: <CAPDyKFqZXdtVokrDQvJAh-NzN0T2ayPD6MepemLEaDt1TRPduw@mail.gmail.com>
Date:   Tue, 1 Sep 2020 17:36:17 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Christoph Hellwig <hch@....de>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Rich Felker <dalias@...c.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 17:06, Christoph Hellwig <hch@....de> wrote:
>
> On Tue, Sep 01, 2020 at 05:04:38PM +0200, Ulf Hansson wrote:
> > +#ifdef CONFIG_HAS_DMA
> > +static int mmc_spi_dma_alloc(struct mmc_spi_host *host)
> > +{
> > +     struct spi_device *spi = host->spi;
> > +     struct device *dev;
> > +
> > +     if (!spi->master->dev.parent->dma_mask)
> > +             return 0;
>
> 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?

Kind regards
Uffe