Messages in this thread Patch in this message | | | Date | Thu, 24 Mar 2022 11:30:38 +0000 | Subject | Re: [PATCH 03/25] dma-direct: take dma-ranges/offsets into account in resource mapping | From | Robin Murphy <> |
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On 2022-03-24 01:48, Serge Semin wrote: > A basic device-specific linear memory mapping was introduced back in > commit ("dma: Take into account dma_pfn_offset") as a single-valued offset > preserved in the device.dma_pfn_offset field, which was initialized for > instance by means of the "dma-ranges" DT property. Afterwards the > functionality was extended to support more than one device-specific region > defined in the device.dma_range_map list of maps. But all of these > improvements concerned a single pointer, page or sg DMA-mapping methods, > while the system resource mapping function turned to miss the > corresponding modification. Thus the dma_direct_map_resource() method now > just casts the CPU physical address to the device DMA address with no > dma-ranges-based mapping taking into account, which is obviously wrong. > Let's fix it by using the phys_to_dma_direct() method to get the > device-specific bus address from the passed memory resource for the case > of the directly mapped DMA.
It may not have been well-documented at the time, but this was largely intentional. The assumption based on known systems was that where dma_pfn_offset existed, it would *not* apply to peer MMIO addresses.
For instance, DTs for TI Keystone 2 platforms only describe an offset for RAM:
dma-ranges = <0x80000000 0x8 0x00000000 0x80000000>;
but a DMA controller might also want to access something in the MMIO range 0x0-0x7fffffff, of which it still has an identical non-offset view. If a driver was previously using dma_map_resource() for that, it would now start getting DMA_MAPPING_ERROR because the dma_range_map exists but doesn't describe the MMIO region. I agree that in hindsight it's not an ideal situation, but it's how things have ended up, so at this point I'm wary of making potentially-breaking changes.
May I ask what exactly your setup looks like, if you have a DMA controller with an offset view of its "own" MMIO space?
Thanks, Robin.
> Fixes: 25f1e1887088 ("dma: Take into account dma_pfn_offset") > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> > --- > kernel/dma/direct.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index 50f48e9e4598..9ce8192b29ab 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -497,7 +497,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents, > dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr, > size_t size, enum dma_data_direction dir, unsigned long attrs) > { > - dma_addr_t dma_addr = paddr; > + dma_addr_t dma_addr = phys_to_dma_direct(dev, paddr); > > if (unlikely(!dma_capable(dev, dma_addr, size, false))) { > dev_err_once(dev,
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