drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c

The use of kmap_atomic() is being deprecated in favor of
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>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231203132947.2328805-8-zhao1.liu@linux.intel.com

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 3626391..756093e 100644 (file)
--- 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;