Messages in this thread | | | Date | Mon, 10 Jul 2023 21:10:25 +0800 | Subject | Re: [PATCH] drm/loongson: Fix two warnings because of passing wrong type | From | suijingfeng <> |
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Hi,
On 2023/7/10 18:26, Jani Nikula wrote: > On Mon, 10 Jul 2023, Sui Jingfeng <suijingfeng@loongson.cn> 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.
> 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@intel.com> >> Closes: https://lore.kernel.org/oe-kbuild-all/202307100243.v3hv6aes-lkp@intel.com/ >> Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn> >> --- >> 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);
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