ACK/Cmnt: [H][PATCH 1/1] drm/i915/ilk-glk: Fix link training on links with LTTPRs

[Stefan Bader]

On 17.08.21 08:18, Aaron Ma wrote:
> From: Imre Deak <imre.deak at intel.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1938999
> 
> The spec requires to use at least 3.2ms for the AUX timeout period if
> there are LT-tunable PHY Repeaters on the link (2.11.2). An upcoming
> spec update makes this more specific, by requiring a 3.2ms minimum
> timeout period for the LTTPR detection reading the 0xF0000-0xF0007
> range (3.6.5.1).
> 
> Accordingly disable LTTPR detection until GLK, where the maximum timeout
> we can set is only 1.6ms.
> 
> Link training in the non-transparent mode is known to fail at least on
> some SKL systems with a WD19 dock on the link, which exposes an LTTPR
> (see the References below). While this could have different reasons
> besides the too short AUX timeout used, not detecting LTTPRs (and so not
> using the non-transparent LT mode) fixes link training on these systems.
> 
> While at it add a code comment about the platform specific maximum
> timeout values.
> 
> v2: Add a comment about the g4x maximum timeout as well. (Ville)
> 
> Reported-by: Takashi Iwai <tiwai at suse.de>
> Reported-and-tested-by: Santiago Zarate <santiago.zarate at suse.com>
> Reported-and-tested-by: Bodo Graumann <mail at bodograumann.de>
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/3166
> Fixes: b30edfd8d0b4 ("drm/i915: Switch to LTTPR non-transparent mode link training")
> Cc: <stable at vger.kernel.org> # v5.11
> Cc: Takashi Iwai <tiwai at suse.de>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/20210317184901.4029798-2-imre.deak@intel.com
> (backported from commit 984982f3ef7b240cd24c2feb2762d81d9d8da3c2)
> Signed-off-by: Aaron Ma <aaron.ma at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

Overall the real change is bailing out of something when on older(? assuming 
lower gen is older) hardware. Which looks to be reasonably tested agains.

-Stefan

>   drivers/gpu/drm/i915/display/intel_dp.c           |  7 +++++++
>   .../gpu/drm/i915/display/intel_dp_link_training.c | 15 ++++++++++++---
>   2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 63e73fbe7a9e..28ead8a3843f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1407,6 +1407,7 @@ static u32 g4x_get_aux_send_ctl(struct intel_dp *intel_dp,
>   	else
>   		precharge = 5;
>   
> +	/* Max timeout value on G4x-BDW: 1.6ms */
>   	if (IS_BROADWELL(dev_priv))
>   		timeout = DP_AUX_CH_CTL_TIME_OUT_600us;
>   	else
> @@ -1433,6 +1434,12 @@ static u32 skl_get_aux_send_ctl(struct intel_dp *intel_dp,
>   	enum phy phy = intel_port_to_phy(i915, dig_port->base.port);
>   	u32 ret;
>   
> +	/*
> +	 * Max timeout values:
> +	 * SKL-GLK: 1.6ms
> +	 * CNL: 3.2ms
> +	 * ICL+: 4ms
> +	 */
>   	ret = DP_AUX_CH_CTL_SEND_BUSY |
>   	      DP_AUX_CH_CTL_DONE |
>   	      DP_AUX_CH_CTL_INTERRUPT |
> 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 fad9e9874c7b..0359d5936901 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -81,6 +81,18 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
>   
>   static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
>   {
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +
> +	if (intel_dp_is_edp(intel_dp))
> +		return false;
> +
> +	/*
> +	 * Detecting LTTPRs must be avoided on platforms with an AUX timeout
> +	 * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
> +	 */
> +	if (INTEL_GEN(i915) < 10)
> +		return false;
> +
>   	if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
>   					  intel_dp->lttpr_common_caps) < 0) {
>   		memset(intel_dp->lttpr_common_caps, 0,
> @@ -126,9 +138,6 @@ int intel_dp_lttpr_init(struct intel_dp *intel_dp)
>   	bool ret;
>   	int i;
>   
> -	if (intel_dp_is_edp(intel_dp))
> -		return 0;
> -
>   	ret = intel_dp_read_lttpr_common_caps(intel_dp);
>   	if (!ret)
>   		return 0;
> 


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