Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: For the problem when using swiotlb | Date | Fri, 21 Nov 2014 18:04:28 +0100 |
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On Friday 21 November 2014 16:57:09 Catalin Marinas wrote: > On Fri, Nov 21, 2014 at 12:48:09PM +0000, Arnd Bergmann wrote: > > On Friday 21 November 2014 09:35:10 Catalin Marinas wrote: > > > +static inline int dma_set_coherent_mask(struct device *dev, u64 mask) > > > +{ > > > + if (!dma_supported(dev, mask)) > > > + return -EIO; > > > + if (mask > dev->coherent_dma_mask) > > > + mask &= of_dma_get_range_mask(dev); > > > + dev->coherent_dma_mask = mask; > > > + return 0; > > > +} > > > > There is an interesting side problem here: the dma mask points to > > coherent_dma_mask for all devices probed from DT, so this breaks > > if we have any driver that sets them to different values. It is a > > preexisting problem them. > > Such drivers would have to set both masks separately (or call > dma_set_mask_and_coherent). What we assume though is that dma-ranges > refers to both dma_mask and coherent_dma_mask. I don't think that would > be a problem for ARM systems.
Right, I'm just saying that we don't have a way to detect drivers that break this assumption, not that we have a serious problem already.
> > > EXPORT_SYMBOL_GPL(of_dma_get_range); > > > > > > +u64 of_dma_get_range_mask(struct device *dev) > > > +{ > > > + u64 dma_addr, paddr, size; > > > + > > > + /* no dma mask limiting if no of_node or no dma-ranges property */ > > > + if (!dev->of_node || > > > + of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size) < 0) > > > + return DMA_BIT_MASK(64); > > > > If no dma-ranges are present, we should assume that the bus only supports > > 32-bit DMA, or we could make it architecture specific. It would probably > > be best for arm64 to require a dma-ranges property for doing any DMA > > at all, but we can't do that on arm32 any more now. > > I thought about this but it could break some existing arm64 DT files if > we mandate dma-ranges property (we could try though). The mask limiting > is arch-specific anyway.
Yes, this has taken far too long to get addressed, we should have added the properties right from the start. If we have a function in architecture specific code, maybe we can just check for the short list of already supported platforms that need backwards compatibility and require the mask for everything else?
> > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > > > index 3b64d0bf5bba..50d1ac4739e6 100644 > > > --- a/drivers/of/platform.c > > > +++ b/drivers/of/platform.c > > > @@ -200,6 +200,10 @@ static void of_dma_configure(struct device *dev) > > > /* DMA ranges found. Calculate and set dma_pfn_offset */ > > > dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr); > > > dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset); > > > + > > > + /* limit the coherent_dma_mask to the dma-ranges size property */ > > > > I would change the comment to clarify that we are actually changing > > the dma_mask here as well. > > > > > + if (size < (1ULL << 32)) > > > + dev->coherent_dma_mask = DMA_BIT_MASK(ilog2(size)); > > > } > > > > As you mentioned in another mail in this thread, we wouldn't be > > able to suuport this case on arm64. > > The mask would still be valid and even usable if an IOMMU is present. Do > you mean we should not limit it at all here?
The code is certainly correct on arm32, as long as we have an appropriate DMA zone.
> There is a scenario where smaller mask would work on arm64. For example > Juno, you can have 2GB of RAM in the 32-bit phys range (starting at > 0x80000000). A device with 31-bit mask and a dma_pfn_offset of > 0x80000000 would still work (there isn't any but just as an example). So > the check in dma_alloc_coherent() would be something like: > > phys_to_dma(top of ZONE_DMA) - dma_pfn_offset <= coherent_dma_mask > > (or assuming RAM starts at 0 and ignoring dma_pfn_offset for now) > > If the condition above fails, dma_alloc_coherent() would no longer fall > back to swiotlb but issue a dev_warn() and return NULL.
Ah, that looks like it should work on all architectures, very nice. How about checking this condition, and then printing a small warning (dev_warn, not WARN_ON) and setting the dma_mask pointer to NULL?
Arnd
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