linux-kernel - Re: [PATCH] drm/i915/display: Add skip link check quirk

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Message-ID: <87a5bsh27o.fsf@intel.com>
Date: Wed, 15 Jan 2025 11:10:35 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Jonathan Denose <jdenose@...gle.com>, LKML <linux-kernel@...r.kernel.org>
Cc: rodrigo.vivi@...el.com, intel-gfx@...ts.freedesktop.org, Jonathan Denose
 <jdenose@...gle.com>, David Airlie <airlied@...il.com>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>, Simona Vetter <simona@...ll.ch>, Tvrtko
 Ursulin <tursulin@...ulin.net>, dri-devel@...ts.freedesktop.org,
 intel-xe@...ts.freedesktop.org, imre.deak@...el.com
Subject: Re: [PATCH] drm/i915/display: Add skip link check quirk

On Tue, 14 Jan 2025, Jonathan Denose <jdenose@...gle.com> wrote:
> The display on the Advantech UTC124G3PWWW0E-ES worked fine until commit
> "drm/i915/dp: Recheck link state after modeset" was introduced. After
> this commit the display flickers intermittently as the driver code
> initiates the delayed link recheck in an infinite loop.
>
> To resolve this issue for the Advantech device, add a quirk to skip over
> the delayed link recheck.

It would be better to try to get at the root cause first, instead of
blindly skipping required parts. The code's complicated enough without
quirks, and removing them afterwards is very difficult.

Please file a bug according to [1], and attach full dmesg with debugs
enabled.

Cc: Imre

BR,
Jani.



[1] https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.html



>
> Signed-off-by: Jonathan Denose <jdenose@...gle.com>
> ---
>
>  drivers/gpu/drm/i915/display/intel_dp_link_training.c | 4 +++-
>  drivers/gpu/drm/i915/display/intel_quirks.c           | 8 ++++++++
>  drivers/gpu/drm/i915/display/intel_quirks.h           | 1 +
>  3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index 397cc4ebae526..7804ad38b00cd 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -32,6 +32,7 @@
>  #include "intel_encoder.h"
>  #include "intel_hotplug.h"
>  #include "intel_panel.h"
> +#include "intel_quirks.h"
>  
>  #define LT_MSG_PREFIX			"[CONNECTOR:%d:%s][ENCODER:%d:%s][%s] "
>  #define LT_MSG_ARGS(_intel_dp, _dp_phy)	(_intel_dp)->attached_connector->base.base.id, \
> @@ -1622,7 +1623,8 @@ void intel_dp_start_link_train(struct intel_atomic_state *state,
>  		lt_dbg(intel_dp, DP_PHY_DPRX, "Forcing link training failure\n");
>  	} else if (passed) {
>  		intel_dp->link.seq_train_failures = 0;
> -		intel_encoder_link_check_queue_work(encoder, 2000);
> +		if (!intel_has_quirk(display, QUIRK_SKIP_LINK_CHECK))
> +			intel_encoder_link_check_queue_work(encoder, 2000);
>  		return;
>  	}
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c b/drivers/gpu/drm/i915/display/intel_quirks.c
> index 28f497ae785bb..d472a5f21f8b9 100644
> --- a/drivers/gpu/drm/i915/display/intel_quirks.c
> +++ b/drivers/gpu/drm/i915/display/intel_quirks.c
> @@ -78,6 +78,12 @@ static void quirk_fw_sync_len(struct intel_dp *intel_dp)
>  	drm_info(display->drm, "Applying Fast Wake sync pulse count quirk\n");
>  }
>  
> +static void quirk_skip_link_check(struct intel_display *display)
> +{
> +	intel_set_quirk(display, QUIRK_SKIP_LINK_CHECK);
> +	drm_info(display->drm, "Applying skip link check quirk\n");
> +}
> +
>  struct intel_quirk {
>  	int device;
>  	int subsystem_vendor;
> @@ -229,6 +235,8 @@ static struct intel_quirk intel_quirks[] = {
>  	{ 0x3184, 0x1019, 0xa94d, quirk_increase_ddi_disabled_time },
>  	/* HP Notebook - 14-r206nv */
>  	{ 0x0f31, 0x103c, 0x220f, quirk_invert_brightness },
> +	/* Advantech UTC124G3PWWW0E-ES */
> +	{0x5a85, 0x8086, 0x2212, quirk_skip_link_check},
>  };
>  
>  static const struct intel_dpcd_quirk intel_dpcd_quirks[] = {
> diff --git a/drivers/gpu/drm/i915/display/intel_quirks.h b/drivers/gpu/drm/i915/display/intel_quirks.h
> index cafdebda75354..9e8f2816a4fba 100644
> --- a/drivers/gpu/drm/i915/display/intel_quirks.h
> +++ b/drivers/gpu/drm/i915/display/intel_quirks.h
> @@ -20,6 +20,7 @@ enum intel_quirk_id {
>  	QUIRK_LVDS_SSC_DISABLE,
>  	QUIRK_NO_PPS_BACKLIGHT_POWER_HOOK,
>  	QUIRK_FW_SYNC_LEN,
> +	QUIRK_SKIP_LINK_CHECK,
>  };
>  
>  void intel_init_quirks(struct intel_display *display);

-- 
Jani Nikula, Intel