Messages in this thread | | | Subject | Re: [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM | From | Robin Murphy <> | Date | Mon, 14 Jan 2019 14:16:46 +0000 |
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On 11/01/2019 18:17, Christoph Hellwig wrote: > Use WARN_ON_ONCE to print a stack trace and return a proper error > code instead.
I was racking my brain to remember the reasoning behind BUG_ON() being the only viable way to prevent errors getting through unhandled, but of course that was before we had a standardised DMA_MAPPING_ERROR that would work across all implementations.
> Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > include/linux/dma-mapping.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index d3087829a6df..91add0751aa5 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -353,7 +353,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev, > BUG_ON(!valid_dma_direction(dir)); > > /* Don't allow RAM to be mapped */
Ugh, I'm pretty sure that that "pfn_valid means RAM" misunderstanding originally came from me - it might be nice to have a less-misleading comment here, but off-hand I can't think of a succinct way to say "only for 'DMA' access to MMIO registers/SRAMs/etc. and not for anything the kernel knows as actual system/device memory" to better explain the WARN...
Either way, though,
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> - BUG_ON(pfn_valid(PHYS_PFN(phys_addr))); > + if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr)))) > + return DMA_MAPPING_ERROR; > > if (dma_is_direct(ops)) > addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs); >
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