Skip to content

WIP: intel/isl: return the correct row pitch for 64 byte alignment

Leandro Ribeiro requested to merge leandrohrb/mesa:intel_wrong_alignment into master

Hello! I've tried to build and run kmscube from source, in order to study and contribute with mesa, and I think that I've found a bug (don't know if it's in mesa or DRM yet). I'm trying to create a patch for it, and I thought that maybe you could help me. The bug description and the PoC that I've made are described below. This is not a definitive solution, since I don't know exactly how to fix it.

For i915 architecture and screens of resolution 1366x768,
the row pitch alignment returned is currently 4 bytes.
edit: i965 driver, not i915 architecture

The framebuffer row pitch is a number >= screen_width*bpb,
(which is 1366*4=5464, for this particular case) that is also
multiple of the alignment value (4 bytes, currently).

However, the kernel requires a row pitch value that is 64 byte
aligned in order to create a framebuffer, and 5464 % 64 != 0

Fix that returning a row pitch alignment of 64.

Signed-off-by: Leandro Ribeiro <>

Laptop specs

  • Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz
  • OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 5500 (Broadwell GT2)
  • There's also an AMD Radeon R5 M230, which I'm not using (idk if this matters)
  • Screen resolution: 1366 x 768
  • OpenGL ES 3.1 Mesa 19.3.0-devel
  • 5.3.5-arch1-1-ARCH

How to reproduce the bug

kmscube error

  • failed to create fb: Invalid argument
  • Failed to get a new framebuffer BO

DRM debug messages

  • [ +0.000039] [drm:intel_framebuffer_init [i915]] plane 0 pitch (5464) must be at least 64 byte aligned
  • [ +0.000012] [drm:drm_internal_framebuffer_create [drm]] could not create framebuffer
  • [ +0.000007] [drm:drm_ioctl [drm]] pid=708, ret = -22
  • Kernel related file: drivers/gpu/drm/i915/display/intel_display.c

What I've done to ""fix"" the error

  • vim mesa/src/intel/isl/isl.c
  • In function isl_calc_row_pitch, the alignment value that ìsl_calc_row_pitch_alignment returns is 4. The function returns in the statement return bs;, for this particular case.
  • If I edit the function isl_calc_row_pitch_alignment to return 64; the kmscube works.
  • The value that isl_calc_min_row_pitch returns is multiple of the alignment value.
  • When alignment is 4, it returns 5464 and then we have the bug. When it's 64, it returns 5504 and everything works, because the kernel requires the row pitch to be 64 byte aligned.
  • As mentioned before, this is just a PoC, since I don't know if the kernel requirement is wrong or if the problem is the value computed by the Intel mesa driver.

Similar bug report and patch

  • Bug report: #1825 (moved)
  • Patch: !1756
  • Didn't work for me: isl_calc_min_row_pitch returns isl_calc_linear_min_row_pitch, since tile_info->tiling == ISL_TILING_LINEAR.
  • So isl_calc_tiled_min_row_pitch, the function edited in the patch, is not being called. It's called only if tile_info->tiling != ISL_TILING_LINEAR.

CC: @jekstrand

Edited by Leandro Ribeiro

Merge request reports