Date:   Mon, 11 Jan 2021 21:07:51 +0200
From:   Jani Nikula <jani.nikula@...el.com>
To:     Lyude Paul <lyude@...hat.com>, intel-gfx@...ts.freedesktop.org
Cc:     thaytan@...aisin.net, Vasily Khoruzhick <anarsoul@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Imre Deak <imre.deak@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Dave Airlie <airlied@...hat.com>,
        Sean Paul <seanpaul@...omium.org>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Uma Shankar <uma.shankar@...el.com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        Ankit Nautiyal <ankit.k.nautiyal@...el.com>,
        Wambui Karuga <wambui.karugax@...il.com>,
        José Roberto de Souza <jose.souza@...el.com>,
        Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@...el.com>,
        Lee Shawn C <shawn.c.lee@...el.com>,
        Anshuman Gupta <anshuman.gupta@...el.com>,
        "open list\:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/4] drm/dp: Revert "drm/dp: Introduce EDID-based quirks"

On Thu, 07 Jan 2021, Lyude Paul <lyude@...hat.com> wrote:
> This reverts commit 0883ce8146ed6074c76399f4e70dbed788582e12. Originally
> these quirks were added because of the issues with using the eDP
> backlight interfaces on certain laptop panels, which made it impossible
> to properly probe for DPCD backlight support without having a whitelist
> for panels that we know have working VESA backlight control interfaces
> over DPCD. As well, it should be noted it was impossible to use the
> normal sink OUI for recognizing these panels as none of them actually
> filled out their OUIs, hence needing to resort to checking EDIDs.
>
> At the time we weren't really sure why certain panels had issues with
> DPCD backlight controls, but we eventually figured out that there was a
> second interface that these problematic laptop panels actually did work
> with and advertise properly: Intel's proprietary backlight interface for
> HDR panels. So far the testing we've done hasn't brought any panels to
> light that advertise this interface and don't support it properly, which
> means we finally have a real solution to this problem.
>
> As a result, we now have no need for the force DPCD backlight quirk, and
> furthermore this also removes the need for any kind of EDID quirk
> checking in DRM. So, let's just revert it for now since we were the only
> driver using this.
>
> v3:
> * Rebase
> v2:
> * Fix indenting error picked up by checkpatch in
>   intel_edp_init_connector()
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Acked-by: Jani Nikula <jani.nikula@...el.com>

Still stands.

BR,
Jani.

> Cc: thaytan@...aisin.net
> Cc: Vasily Khoruzhick <anarsoul@...il.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c               | 83 +------------------
>  drivers/gpu/drm/drm_dp_mst_topology.c         |  3 +-
>  .../drm/i915/display/intel_display_types.h    |  1 -
>  drivers/gpu/drm/i915/display/intel_dp.c       |  9 +-
>  drivers/gpu/drm/i915/display/intel_dp_mst.c   |  3 +-
>  drivers/gpu/drm/i915/display/intel_psr.c      |  2 +-
>  include/drm/drm_dp_helper.h                   | 21 +----
>  7 files changed, 9 insertions(+), 113 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 3ecde451f523..19dbdeb581cb 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -1236,7 +1236,7 @@ bool drm_dp_read_sink_count_cap(struct drm_connector *connector,
>  	return connector->connector_type != DRM_MODE_CONNECTOR_eDP &&
>  		dpcd[DP_DPCD_REV] >= DP_DPCD_REV_11 &&
>  		dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT &&
> -		!drm_dp_has_quirk(desc, 0, DP_DPCD_QUIRK_NO_SINK_COUNT);
> +		!drm_dp_has_quirk(desc, DP_DPCD_QUIRK_NO_SINK_COUNT);
>  }
>  EXPORT_SYMBOL(drm_dp_read_sink_count_cap);
>  
> @@ -1957,87 +1957,6 @@ drm_dp_get_quirks(const struct drm_dp_dpcd_ident *ident, bool is_branch)
>  #undef DEVICE_ID_ANY
>  #undef DEVICE_ID
>  
> -struct edid_quirk {
> -	u8 mfg_id[2];
> -	u8 prod_id[2];
> -	u32 quirks;
> -};
> -
> -#define MFG(first, second) { (first), (second) }
> -#define PROD_ID(first, second) { (first), (second) }
> -
> -/*
> - * Some devices have unreliable OUIDs where they don't set the device ID
> - * correctly, and as a result we need to use the EDID for finding additional
> - * DP quirks in such cases.
> - */
> -static const struct edid_quirk edid_quirk_list[] = {
> -	/* Optional 4K AMOLED panel in the ThinkPad X1 Extreme 2nd Generation
> -	 * only supports DPCD backlight controls
> -	 */
> -	{ MFG(0x4c, 0x83), PROD_ID(0x41, 0x41), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	/*
> -	 * Some Dell CML 2020 systems have panels support both AUX and PWM
> -	 * backlight control, and some only support AUX backlight control. All
> -	 * said panels start up in AUX mode by default, and we don't have any
> -	 * support for disabling HDR mode on these panels which would be
> -	 * required to switch to PWM backlight control mode (plus, I'm not
> -	 * even sure we want PWM backlight controls over DPCD backlight
> -	 * controls anyway...). Until we have a better way of detecting these,
> -	 * force DPCD backlight mode on all of them.
> -	 */
> -	{ MFG(0x06, 0xaf), PROD_ID(0x9b, 0x32), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	{ MFG(0x06, 0xaf), PROD_ID(0xeb, 0x41), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	{ MFG(0x4d, 0x10), PROD_ID(0xc7, 0x14), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	{ MFG(0x4d, 0x10), PROD_ID(0xe6, 0x14), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	{ MFG(0x4c, 0x83), PROD_ID(0x47, 0x41), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -	{ MFG(0x09, 0xe5), PROD_ID(0xde, 0x08), BIT(DP_QUIRK_FORCE_DPCD_BACKLIGHT) },
> -};
> -
> -#undef MFG
> -#undef PROD_ID
> -
> -/**
> - * drm_dp_get_edid_quirks() - Check the EDID of a DP device to find additional
> - * DP-specific quirks
> - * @edid: The EDID to check
> - *
> - * While OUIDs are meant to be used to recognize a DisplayPort device, a lot
> - * of manufacturers don't seem to like following standards and neglect to fill
> - * the dev-ID in, making it impossible to only use OUIDs for determining
> - * quirks in some cases. This function can be used to check the EDID and look
> - * up any additional DP quirks. The bits returned by this function correspond
> - * to the quirk bits in &drm_dp_quirk.
> - *
> - * Returns: a bitmask of quirks, if any. The driver can check this using
> - * drm_dp_has_quirk().
> - */
> -u32 drm_dp_get_edid_quirks(const struct edid *edid)
> -{
> -	const struct edid_quirk *quirk;
> -	u32 quirks = 0;
> -	int i;
> -
> -	if (!edid)
> -		return 0;
> -
> -	for (i = 0; i < ARRAY_SIZE(edid_quirk_list); i++) {
> -		quirk = &edid_quirk_list[i];
> -		if (memcmp(quirk->mfg_id, edid->mfg_id,
> -			   sizeof(edid->mfg_id)) == 0 &&
> -		    memcmp(quirk->prod_id, edid->prod_code,
> -			   sizeof(edid->prod_code)) == 0)
> -			quirks |= quirk->quirks;
> -	}
> -
> -	DRM_DEBUG_KMS("DP sink: EDID mfg %*phD prod-ID %*phD quirks: 0x%04x\n",
> -		      (int)sizeof(edid->mfg_id), edid->mfg_id,
> -		      (int)sizeof(edid->prod_code), edid->prod_code, quirks);
> -
> -	return quirks;
> -}
> -EXPORT_SYMBOL(drm_dp_get_edid_quirks);
> -
>  /**
>   * drm_dp_read_desc - read sink/branch descriptor from DPCD
>   * @aux: DisplayPort AUX channel
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 0401b2f47500..a2e692a0c6c2 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -5824,8 +5824,7 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
>  	if (drm_dp_read_desc(port->mgr->aux, &desc, true))
>  		return NULL;
>  
> -	if (drm_dp_has_quirk(&desc, 0,
> -			     DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) &&
> +	if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) &&
>  	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14 &&
>  	    port->parent == port->mgr->mst_primary) {
>  		u8 downstreamport;
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index b24d80ffd18b..744bdf39a7b1 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1390,7 +1390,6 @@ struct intel_dp {
>  	int max_link_rate;
>  	/* sink or branch descriptor */
>  	struct drm_dp_desc desc;
> -	u32 edid_quirks;
>  	struct drm_dp_aux aux;
>  	u32 aux_busy_last_status;
>  	u8 train_set[4];
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 8a00e609085f..7fcb8ca10f96 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -162,8 +162,7 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
>  	int i, max_rate;
>  	int max_lttpr_rate;
>  
> -	if (drm_dp_has_quirk(&intel_dp->desc, 0,
> -			     DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS)) {
> +	if (drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS)) {
>  		/* Needed, e.g., for Apple MBP 2017, 15 inch eDP Retina panel */
>  		static const int quirk_rates[] = { 162000, 270000, 324000 };
>  
> @@ -2823,8 +2822,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  	struct intel_connector *intel_connector = intel_dp->attached_connector;
>  	struct intel_digital_connector_state *intel_conn_state =
>  		to_intel_digital_connector_state(conn_state);
> -	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, 0,
> -					   DP_DPCD_QUIRK_CONSTANT_N);
> +	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
>  	int ret = 0, output_bpp;
>  
>  	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && port != PORT_A)
> @@ -7007,7 +7005,6 @@ intel_dp_set_edid(struct intel_dp *intel_dp)
>  	}
>  
>  	drm_dp_cec_set_edid(&intel_dp->aux, edid);
> -	intel_dp->edid_quirks = drm_dp_get_edid_quirks(edid);
>  }
>  
>  static void
> @@ -7021,7 +7018,6 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
>  
>  	intel_dp->has_hdmi_sink = false;
>  	intel_dp->has_audio = false;
> -	intel_dp->edid_quirks = 0;
>  
>  	intel_dp->dfp.max_bpc = 0;
>  	intel_dp->dfp.max_dotclock = 0;
> @@ -8425,7 +8421,6 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
>  	if (edid) {
>  		if (drm_add_edid_modes(connector, edid)) {
>  			drm_connector_update_edid_property(connector, edid);
> -			intel_dp->edid_quirks = drm_dp_get_edid_quirks(edid);
>  		} else {
>  			kfree(edid);
>  			edid = ERR_PTR(-EINVAL);
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 27f04aed8764..3e7bbf8d6620 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -53,8 +53,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>  	struct drm_i915_private *i915 = to_i915(connector->base.dev);
>  	const struct drm_display_mode *adjusted_mode =
>  		&crtc_state->hw.adjusted_mode;
> -	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, 0,
> -					   DP_DPCD_QUIRK_CONSTANT_N);
> +	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
>  	int bpp, slots = -EINVAL;
>  
>  	crtc_state->lane_count = limits->max_lane_count;
> diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
> index c24ae69426cf..1e6c1fa59d4a 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr.c
> +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> @@ -305,7 +305,7 @@ void intel_psr_init_dpcd(struct intel_dp *intel_dp)
>  	drm_dbg_kms(&dev_priv->drm, "eDP panel supports PSR version %x\n",
>  		    intel_dp->psr_dpcd[0]);
>  
> -	if (drm_dp_has_quirk(&intel_dp->desc, 0, DP_DPCD_QUIRK_NO_PSR)) {
> +	if (drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_NO_PSR)) {
>  		drm_dbg_kms(&dev_priv->drm,
>  			    "PSR support not currently available for this panel\n");
>  		return;
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 6236f212da61..edffd1dcca3e 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -2029,16 +2029,13 @@ struct drm_dp_desc {
>  
>  int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
>  		     bool is_branch);
> -u32 drm_dp_get_edid_quirks(const struct edid *edid);
>  
>  /**
>   * enum drm_dp_quirk - Display Port sink/branch device specific quirks
>   *
>   * Display Port sink and branch devices in the wild have a variety of bugs, try
>   * to collect them here. The quirks are shared, but it's up to the drivers to
> - * implement workarounds for them. Note that because some devices have
> - * unreliable OUIDs, the EDID of sinks should also be checked for quirks using
> - * drm_dp_get_edid_quirks().
> + * implement workarounds for them.
>   */
>  enum drm_dp_quirk {
>  	/**
> @@ -2070,16 +2067,6 @@ enum drm_dp_quirk {
>  	 * The DSC caps can be read from the physical aux instead.
>  	 */
>  	DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD,
> -	/**
> -	 * @DP_QUIRK_FORCE_DPCD_BACKLIGHT:
> -	 *
> -	 * The device is telling the truth when it says that it uses DPCD
> -	 * backlight controls, even if the system's firmware disagrees. This
> -	 * quirk should be checked against both the ident and panel EDID.
> -	 * When present, the driver should honor the DPCD backlight
> -	 * capabilities advertised.
> -	 */
> -	DP_QUIRK_FORCE_DPCD_BACKLIGHT,
>  	/**
>  	 * @DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS:
>  	 *
> @@ -2092,16 +2079,14 @@ enum drm_dp_quirk {
>  /**
>   * drm_dp_has_quirk() - does the DP device have a specific quirk
>   * @desc: Device descriptor filled by drm_dp_read_desc()
> - * @edid_quirks: Optional quirk bitmask filled by drm_dp_get_edid_quirks()
>   * @quirk: Quirk to query for
>   *
>   * Return true if DP device identified by @desc has @quirk.
>   */
>  static inline bool
> -drm_dp_has_quirk(const struct drm_dp_desc *desc, u32 edid_quirks,
> -		 enum drm_dp_quirk quirk)
> +drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
>  {
> -	return (desc->quirks | edid_quirks) & BIT(quirk);
> +	return desc->quirks & BIT(quirk);
>  }
>  
>  #ifdef CONFIG_DRM_DP_CEC

-- 
Jani Nikula, Intel Open Source Graphics Center

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