Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when CONFIG_HAS_DMA is unset

[Rich Felker]

On Wed, Sep 02, 2020 at 05:51:16PM +0200, Geert Uytterhoeven wrote:
> Hi Rich,
> 
> On Wed, Sep 2, 2020 at 5:43 PM Rich Felker <dalias@xxxxxxxx> wrote:
> > On Wed, Sep 02, 2020 at 10:31:47AM +0200, Ulf Hansson wrote:
> > > On Tue, 1 Sep 2020 at 17:40, Christoph Hellwig <hch@xxxxxx> 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.
> >
> > DMA support was always optional, because even on systems where DMA is
> > present, it doesn't necessarily mean the SPI controller uses DMA. In
> > particular, pure bit-banged SPI via GPIOs doesn't have DMA, but has
> > always worked. See my previous reply to Christoph about host->dma_dev
> > for my current-best understanding of what's going on here.
> >
> > > 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.
> >
> > I'll rebuild and retest just to confirm, but I already tested a
> > functionally equivalent patch that just did the #ifdef inline (rather
> > than moving the logic out to separate functions) and it worked fine.
> 
> Hence, Tested-by? ;-)

Confirmed that this version of the patch works too. Thus,

Tested-by: Rich Felker <dalias@xxxxxxxx>