[PATCH 0/3] drm/i915: Fix scanline_offset for LNL+/BMG+

[Gustavo Sousa]

Quoting Lucas De Marchi (2025-02-07 19:41:11-03:00)
>On Fri, Feb 07, 2025 at 11:54:03PM +0200, Ville Syrjälä wrote:
>>From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>>
>>Something has changed in the hardware on LNL/BMG because
>>HDMI outputs no longer have the extra scanline offset.
>>
>>I confirmed that MTL still has the old behaviour, which
>>is a bit weird since both MTL and BMG have display ver 14
>>vs. LNL is version 20. But can't argue with actual
>>hardware behaviour.
>
><6>[  210.368608] xe 0000:03:00.0: [drm] Found battlemage (device ID e20b) discrete display version 14.01 stepping B0
>vs
><6>[  412.999204] i915 0000:00:02.0: [drm] Found meteorlake (device ID 7d55) integrated display version 14.00 stepping C0
>
>So 14.01 vs 14.00. In the driver:
>
>static const struct {                                                            
>         u16 ver;
>         u16 rel;
>         const struct intel_display_device_info *display;
>} gmdid_display_map[] = {
>         { 14,  0, &xe_lpdp_display },
>         { 14,  1, &xe2_hpd_display },
>        ...
>}
>
>So maybe we need to check for the full version >= 1401 instead?

Yeah, I think just checking for version >= 14.01 would make sense here.

>
>+Matt Roper, +Gustavo who may know the right bspec to confirm this
>change in behavior

I haven't found any bspec that explains the behavior of the counter
outside of the bspec page for the scanline register itself, which seems
to have the same description across different platforms.

--
Gustavo Sousa

>
>Lucas De Marchi
>
>>
>>Ville Syrjälä (3):
>>  drm/i915: Fix scanline_offset for LNL+ and BMG+
>>  drm/i915: Reverse the scanline_offset if ladder
>>  drm/i915: Replace the HAS_DDI() in intel_crtc_scanline_offset() with
>>    specific platform checks
>>
>> drivers/gpu/drm/i915/display/intel_vblank.c | 13 ++++++++-----
>> 1 file changed, 8 insertions(+), 5 deletions(-)
>>
>>-- 
>>2.45.3
>>