[PATCH v3 7/9] drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c

Zhao Liu
2023-12-03T13:18:31Z

kmap_local_page()[1], and this patch converts the call from
kmap_atomic() to kmap_local_page().

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults or preemption disables.

In drm/i915/gt/uc/intel_us_fw.c, the function intel_uc_fw_copy_rsa()
just use the mapping to do memory copy so it doesn't need to disable
pagefaults and preemption for mapping. Thus the local mapping without
atomic context (not disable pagefaults / preemption) is enough.

Therefore, intel_uc_fw_copy_rsa() is a function where the use of
memcpy_from_page() with kmap_local_page() in place of memcpy() with
kmap_atomic() is correctly suited.

Convert the calls of memcpy() with kmap_atomic() / kunmap_atomic() to
memcpy_from_page() which uses local mapping to copy.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/T/#u

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
Suggested by credits:
Ira: Referred to his task document and suggestions about using
memcpy_from_page() directly.
Fabio: Referred to his boiler plate commit message and his description
about why kmap_local_page() should be preferred.
---
drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
index 362639162ed6..756093eaf2ad 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
@@ -1343,16 +1343,13 @@ size_t intel_uc_fw_copy_rsa(struct intel_uc_fw *uc_fw, void *dst, u32 max_len)

for_each_sgt_page(page, iter, uc_fw->obj->mm.pages) {
u32 len = min_t(u32, size, PAGE_SIZE - offset);
- void *vaddr;

if (idx > 0) {
idx--;
continue;
}

- vaddr = kmap_atomic(page);
- memcpy(dst, vaddr + offset, len);
- kunmap_atomic(vaddr);
+ memcpy_from_page(dst, page, offset, len);

offset = 0;
dst += len;
--
2.34.1