On Mon, 10 Jul 2023, suijingfeng <suijingfeng@xxxxxxxxxxx> wrote: > Hi, > > On 2023/7/10 18:26, Jani Nikula wrote: >> On Mon, 10 Jul 2023, Sui Jingfeng <suijingfeng@xxxxxxxxxxx> wrote: >>> When accessing I/O memory, we should pass '__iomem *' type instead of >>> 'void *' simply, otherwise sparse tests will complain. After applied >>> this patch, the following two sparse warnings got fixed. >> Usually the commit message should explain why it's okay to cast away the >> warning. >> >> Because realistically this doesn't "fix" the warning, this merely hides >> it. > > > My understanding is that a point itself is just a variable where store a > address, > > if this address originally point to I/O memory, > > then, we can other cast it to u64 type, then cast it back to '__iomem *' > again. > > as long as the type's bit-width is width enough to store this address, > we won't lost the information. > > > 'void *' or 'u64' is just a intermediate represent of the address. > > we can other cast it to u64 type, then cast it back to 'void __iomem *' > or 'void *' again. > > > Why it's okay ? My answer is that > > As long as a address is really point to the I/O memory, cast it to 'void > __iomem *' is OK. > > As long as a address is really point to the system memory, cast it to > 'void *' is OK. The point of __iomem is to have sparse help you in tracking that, so you don't accidentally mix up the two. BR, Jani. > > >> BR, >> Jani. >> >>> 1) drivers/gpu/drm/loongson/lsdc_benchmark.c:27:35: >>> sparse: expected void volatile [noderef] __iomem * >>> sparse: got void *kptr >>> >>> 2) drivers/gpu/drm/loongson/lsdc_benchmark.c:42:51: >>> sparse: expected void const volatile [noderef] __iomem * >>> sparse: got void *kptr >>> >>> Reported-by: kernel test robot <lkp@xxxxxxxxx> >>> Closes: https://lore.kernel.org/oe-kbuild-all/202307100243.v3hv6aes-lkp@xxxxxxxxx/ >>> Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx> >>> --- >>> drivers/gpu/drm/loongson/lsdc_benchmark.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/loongson/lsdc_benchmark.c b/drivers/gpu/drm/loongson/lsdc_benchmark.c >>> index b088646a2ff9..36e352820bdb 100644 >>> --- a/drivers/gpu/drm/loongson/lsdc_benchmark.c >>> +++ b/drivers/gpu/drm/loongson/lsdc_benchmark.c >>> @@ -24,7 +24,7 @@ static void lsdc_copy_gtt_to_vram_cpu(struct lsdc_bo *src_bo, >>> lsdc_bo_kmap(dst_bo); >>> >>> while (n--) >>> - memcpy_toio(dst_bo->kptr, src_bo->kptr, size); >>> + memcpy_toio((void __iomem *)dst_bo->kptr, src_bo->kptr, size); >>> >>> lsdc_bo_kunmap(src_bo); >>> lsdc_bo_kunmap(dst_bo); >>> @@ -39,7 +39,7 @@ static void lsdc_copy_vram_to_gtt_cpu(struct lsdc_bo *src_bo, >>> lsdc_bo_kmap(dst_bo); >>> >>> while (n--) >>> - memcpy_fromio(dst_bo->kptr, src_bo->kptr, size); >>> + memcpy_fromio(dst_bo->kptr, (void __iomem *)src_bo->kptr, size); >>> >>> lsdc_bo_kunmap(src_bo); >>> lsdc_bo_kunmap(dst_bo); > -- Jani Nikula, Intel Open Source Graphics Center
