Commit 9d2d4902 authored by Loïc Molinari's avatar Loïc Molinari Committed by Boris Brezillon
Browse files

drm/shmem-helper: Simplify page offset calculation in fault handler 



For a fault at address addr, the page offset is
  page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT
              = ((addr & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT
	      = (addr - vma->vm_start) >> PAGE_SHIFT

Since the faulty logical page offset based on VMA is
  vmf->pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)

We can slightly simplify the calculation using
  page_offset = vmf->pgoff - vma->vm_pgoff

v11:
- remove misleading comment
- add Boris R-b

Signed-off-by: default avatarLoïc Molinari <loic.molinari@collabora.com>
Reviewed-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20251205182231.194072-2-loic.molinari@collabora.com


Signed-off-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
parent d8f94cb0

drivers/gpu/drm/drm_gem_shmem_helper.c

+2 −2
Original line number Diff line number Diff line
@@ -577,8 +577,8 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) 
	struct page *page;

	pgoff_t page_offset;



	/* We don't use vmf->pgoff since that has the fake offset */

	page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;

	/* Offset to faulty address in the VMA. */

	page_offset = vmf->pgoff - vma->vm_pgoff;



	dma_resv_lock(shmem->base.resv, NULL);