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

[Christoph Hellwig]

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.