[Intel-gfx] [PATCH] drm/i915/dp: Fix alt mode handling.

[Maarten Lankhorst]

Op 13-03-18 om 15:27 schreef Ville Syrjälä:
> On Tue, Mar 13, 2018 at 02:52:35PM +0100, Maarten Lankhorst wrote:
>> On fi-cnl-y3 we have 2 modes that differ only by crtc_clock. This means
>> that if we request the normal mode, we automatically get the downclocked
>> mode.
>>
>> This can be seen during boot:
>> [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:101:eDP-1] probed modes :
>> [drm:drm_mode_debug_printmodeline] Modeline 102:"3840x2160" 60 533250 3840 3888 3920 4000 2160 2163 2168 2222 0x48 0xa
>> [drm:drm_mode_debug_printmodeline] Modeline 103:"3840x2160" 48 426600 3840 3888 3920 4000 2160 2163 2168 2222 0x40 0xa
>> ...
>> [drm:intel_dump_pipe_config [i915]] [CRTC:51:pipe A][modeset]
>> [drm:intel_dump_pipe_config [i915]] output_types: EDP (0x100)
>> [drm:intel_dump_pipe_config [i915]] cpu_transcoder: EDP, pipe bpp: 24, dithering: 0
>> [drm:intel_dump_pipe_config [i915]] dp m_n: lanes: 4; gmch_m: 4970250, gmch_n: 8388608, link_m: 828375, link_n: 1048576, tu: 64
>> [drm:intel_dump_pipe_config [i915]] dp m2_n2: lanes: 4; gmch_m: 4970250, gmch_n: 8388608, link_m: 828375, link_n: 1048576, tu: 64
>> [drm:intel_dump_pipe_config [i915]] audio: 0, infoframes: 0
>> [drm:intel_dump_pipe_config [i915]] requested mode:
>> [drm:drm_mode_debug_printmodeline] Modeline 0:"3840x2160" 60 533250 3840 3888 3920 4000 2160 2163 2168 2222 0x48 0xa
>> [drm:intel_dump_pipe_config [i915]] adjusted mode:
>> [drm:drm_mode_debug_printmodeline] Modeline 0:"3840x2160" 48 426600 3840 3888 3920 4000 2160 2163 2168 2222 0x40 0xa
>>
>> Add a intel_edp_choose_mode helper that picks the mode.
>>
>> If there is no alt mode, it always picks the default mode.
>> If the alt mode is identical to the default mode, it picks the mode
>> based on what mode is closest to the request clock.
>> If the alt mode differs, it only picks the alt mode on exact match.
>>
>> Testcase: kms_panel_fitting.atomic-fastset
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>> Fixes: dc911f5bd8aa ("drm/i915/edp: Allow alternate fixed mode for eDP if available.")
>> Cc: David Weinehall <david.weinehall at linux.intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
>> Cc: Jani Nikula <jani.nikula at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Jim Bride <jim.bride at linux.intel.com>
>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>> Cc: <stable at vger.kernel.org> # v4.14+
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105469
>> References: https://bugs.freedesktop.org/show_bug.cgi?id=105456
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 39 +++++++++++++++++++++------------------
>>  1 file changed, 21 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 9a4a51e79fa1..075981842a7f 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -1671,21 +1671,25 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
>>  	return bpp;
>>  }
>>  
>> -static bool intel_edp_compare_alt_mode(struct drm_display_mode *m1,
>> -				       struct drm_display_mode *m2)
>> +static const struct drm_display_mode *
>> +intel_edp_choose_mode(const struct drm_display_mode *req,
>> +		      const struct drm_display_mode *def,
>> +		      const struct drm_display_mode *alt)
>>  {
>> -	bool bres = false;
>> +	if (!alt)
>> +		return def;
>>  
>> -	if (m1 && m2)
>> -		bres = (m1->hdisplay == m2->hdisplay &&
>> -			m1->hsync_start == m2->hsync_start &&
>> -			m1->hsync_end == m2->hsync_end &&
>> -			m1->htotal == m2->htotal &&
>> -			m1->vdisplay == m2->vdisplay &&
>> -			m1->vsync_start == m2->vsync_start &&
>> -			m1->vsync_end == m2->vsync_end &&
>> -			m1->vtotal == m2->vtotal);
>> -	return bres;
>> +	if (drm_mode_equal_no_clocks(def, alt)) {
>> +		int clock;
>> +
>> +		if (!drm_mode_equal_no_clocks(req, def))
>> +			return def;
>> +
>> +		clock = def->clock / 2 + alt->clock / 2;
>> +
>> +		return req->clock > clock ? def : alt;
>> +	} else
>> +		return drm_mode_equal_no_clocks(req, alt) ? alt : def;
> Seems a bit convoluted to me.
>
> return user_mode->vrefresh > alt_mode->vrefresh ?
> 	fixed_mode : alt_mode;
>
> maybe?
>
> Though we don't seem to try very hard to make vrefresh accurate so not
> 100% this is going to work perfectly.
>
> I guess we could go with the "pick the closest" vrefresh approach
> instead. I'm thinking we should actually be rejecting the user mode
> entirely if it isn't closeto either refresh rate.
There's no guarantee vrefresh is set to something sane, afaik. I don't think we can use it.
If it was always set, then maybe. But I think nothing prevents it from being garbage.

~Maarten