Fix a MIPS `dma_alloc_coherent' regression from commit bc3ec75de545 ("dma-mapping: merge direct and noncoherent ops") that causes a cached allocation to be returned on noncoherent cache systems.

This is due to an inverted check now used in the MIPS implementation of `arch_dma_alloc' on the result from `dma_direct_alloc_pages' before doing the cached-to-uncached mapping of the allocation address obtained. The mapping has to be done for a non-NULL rather than NULL result, because a NULL result means the allocation has failed.

Invert the check for correct operation then.

Signed-off-by: Maciej W. Rozycki macro@linux-mips.org Fixes: bc3ec75de545 ("dma-mapping: merge direct and noncoherent ops") Cc: stable@vger.kernel.org # 4.19+ --- On Thu, 1 Nov 2018, Christoph Hellwig wrote:

Fails to compile for me with:

cc1: error: ‘-march=r3000’ requires ‘-mfp32’

using the x86_64 corss gcc 8 from Debian testing.

Hmm, that seems related to the FPXX ABI, which the R3000 does not support and which they may have configured as the default for GCC (`-mfpxx'). That's not relevant to the kernel, so we probably just ought to force `-mfp32' and `-mfp64' for 32-bit and 64-bit builds respectively these days.

Either way the config looks like we have all the required bits for non-coherent dma support. The only guess is that somehow dma_cache_wback_inv aren't hooked up to the right functions for some reason, but I can't really think off why.

Well, `dma_cache_wback_inv' isn't actually called and with the 64-bit configuration I switched to the address returned is in the XKPHYS cached noncoherent space, as proved with a simple diagnostic patch applied to `dma_direct_alloc' showing the results of `dev_is_dma_coherent' and the actual allocation:

tc1: DEFTA at MMIO addr = 0x1e900000, IRQ = 20, Hardware addr = 08-00-2b-a3-a3-29 defxx tc1: dma_direct_alloc: coherent: 0 defxx tc1: dma_direct_alloc: returned: 9800000003db8000 tc1: registered as fddi0

(the value of 3 in bits 61:59 of the virtual address denotes the cached noncoherent attribute).

The cause is commit bc3ec75de545 ("dma-mapping: merge direct and noncoherent ops") reversed the interpretation of the `dma_direct_alloc*' result in `arch_dma_alloc'. I guess this change was unlucky not to have this part of the API actually verified at run-time by anyone anywhere.

Fixed thus, with debug output now as expected:

defxx tc1: dma_direct_alloc: coherent: 0 defxx tc1: dma_direct_alloc: returned: 9000000003db8000

showing the address returned in the XKPHYS uncached space (the value of 2 in bits 61:59 of the virtual address denotes the uncached attribute), and the network interface working properly.

Please apply, and backport as required.

Maciej --- arch/mips/mm/dma-noncoherent.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

linux-mips-arch-dma-alloc-err.patch Index: linux-20181028-4maxp64-defconfig/arch/mips/mm/dma-noncoherent.c =================================================================== --- linux-20181028-4maxp64-defconfig.orig/arch/mips/mm/dma-noncoherent.c +++ linux-20181028-4maxp64-defconfig/arch/mips/mm/dma-noncoherent.c @@ -50,7 +50,7 @@ void *arch_dma_alloc(struct device *dev, void *ret;

ret = dma_direct_alloc_pages(dev, size, dma_handle, gfp, attrs); - if (!ret && !(attrs & DMA_ATTR_NON_CONSISTENT)) { + if (ret && !(attrs & DMA_ATTR_NON_CONSISTENT)) { dma_cache_wback_inv((unsigned long) ret, size); ret = (void *)UNCAC_ADDR(ret); }