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@xxxxxxxxxxxxxxxxxxxx> --- 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,
