Messages in this thread | | | From | Ulf Hansson <> | Date | Mon, 31 Aug 2020 13:28:50 +0200 | Subject | Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU |
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On Sat, 29 Aug 2020 at 10:31, Christoph Hellwig <hch@lst.de> wrote: > > On Fri, Aug 28, 2020 at 11:09:43AM -0400, Rich Felker wrote: > > > However, by looking at the code, one get the feeling that the DMA > > > support is somewhat prepared to be made optional. I guess it has never > > > been really tested, as the Kconfig option has "depends on HAS_DMA" - > > > and it's been like that as long as I can remember. > > > > It always worked on our "byte-banged" SPI controller, with no DMA > > controller present, before Christoph's changes in this patch series, > > Before that nommu sh builds provided a DMA mapping implementation > that even worked for the streaming side (dma_map_*), but would corrupt > data if you used dma_alloc_coherent memory to communicate with the > device.
I see.
> > > and seems to be working now (although I have some other, hopefully > > unrelated regressions to debug) with #ifdef CONFIG_HAS_DMA around the > > if (spi->master->dev.parent->dma_mask) block in mmc_spi_probe. That's > > probably not the right fix though -- why isn't it checking > > host->dma_dev instead and only attempting DMA setup if dma_dev is > > non-null? > > I don't think dma_dev can be NULL right now. dma_dev is assigned here: > > if (spi->master->dev.parent->dma_mask) { > struct device *dev = spi->master->dev.parent; > > host->dma_dev = dev; > > but for any OF or real bus device dma_mask never is zero (it actually is > a pointer), and the value of it also is initialized to 32-bit by default, > making this effectively an "if (1) {". The driver needs some way to > communicate if a given device actually is DMA capable or not. Or is that > purely a factor of the platform which would be a little strange.
Okay, thanks for clarifying things.
> > In which case we should do something like: > > > diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c > index 39bb1e30c2d722..3b0cc9a70e6432 100644 > --- a/drivers/mmc/host/mmc_spi.c > +++ b/drivers/mmc/host/mmc_spi.c > @@ -1374,7 +1374,7 @@ static int mmc_spi_probe(struct spi_device *spi) > if (!host->data) > goto fail_nobuf1; > > - if (spi->master->dev.parent->dma_mask) { > + if (IS_ENABLED(CONFIG_HAS_DMA)) {
I guess "#ifdef CONFIG_HAS_DMA", would work as well as CONFIG_HAS_DMA can't be "m".
I would also suggest moving the DMA setup things into a separate function. Then when CONFIG_HAS_DMA is unset, we can use a stub.
> struct device *dev = spi->master->dev.parent; > > host->dma_dev = dev;
Let me cook a patch that we can try.
Kind regards Uffe
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