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.
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);
