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

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Message-ID: <20200901154049.GA376@lst.de>
Date:   Tue, 1 Sep 2020 17:40:49 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Christoph Hellwig <hch@....de>,
        "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, 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
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.