Re: [Intel-gfx] [PATCH] drm/i915/combo_phy: Add Workaround to avoid flicker with HBR3 eDP Panels

[Imre Deak <imre.deak@intel.com>]

On Thu, Aug 04, 2022 at 03:59:11PM +0530, Ankit Nautiyal wrote:
> WA_14014367875 : When Display PHY is configured in continuous
> DCC calibration mode, the DCC (duty cycle correction) for the clock
> erroneously goes through a state where the DCC code is 0x00 when it is
> supposed to be transitioning from 0x10 to 0x0F. This glitch causes a
> distortion in the clock, which leads to a bit error. The issue is known
> to be causing flickering with eDP HBR3 panels.
> 
> The work around configures the DCC in one-time-update mode.
> This mode updates the DCC code one time during training and then
> it does not change.  This will prevent on-the-fly updates so that the
> glitch does not occur.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_combo_phy.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_combo_phy.c b/drivers/gpu/drm/i915/display/intel_combo_phy.c
> index 64890f39c3cc..1b8bdc47671d 100644
> --- a/drivers/gpu/drm/i915/display/intel_combo_phy.c
> +++ b/drivers/gpu/drm/i915/display/intel_combo_phy.c
> @@ -242,9 +242,10 @@ static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
>  				     ICL_PORT_TX_DW8_ODCC_CLK_SEL |
>  				     ICL_PORT_TX_DW8_ODCC_CLK_DIV_SEL_DIV2);
>  
> +		/* WA_14014367875 Set DCC calibration mode to Read once*/

The usual format is 'Wa_<lineage>:<platforms>', so Wa_22012718247:...
'read once' is 'run once' afaics.

>  		ret &= check_phy_reg(dev_priv, phy, ICL_PORT_PCS_DW1_LN(0, phy),
>  				     DCC_MODE_SELECT_MASK,
> -				     DCC_MODE_SELECT_CONTINUOSLY);
> +				     ~DCC_MODE_SELECT_MASK);

I can see this WA listed only for ADL_P/N/S and TGL (and not for DG2/RKL
for instance). ~DCC_MODE_SELECT_MASK should be 0, maybe add a
dcc_calibration_mode() that could be used below as well.

Could you file a ticket at
https://gfxspecs.intel.com/Predator/Home/Index/49291
which specifies this programming explicitly for each platform, but is
incorrect now wrt. the above WA?

>  	}
>  
>  	ret &= icl_verify_procmon_ref_values(dev_priv, phy);
> @@ -366,8 +367,9 @@ static void icl_combo_phys_init(struct drm_i915_private *dev_priv)
>  			intel_de_write(dev_priv, ICL_PORT_TX_DW8_GRP(phy), val);
>  
>  			val = intel_de_read(dev_priv, ICL_PORT_PCS_DW1_LN(0, phy));
> +
> +			/* WA_14014367875 Set DCC calibration mode to Read once*/
>  			val &= ~DCC_MODE_SELECT_MASK;
> -			val |= DCC_MODE_SELECT_CONTINUOSLY;
>  			intel_de_write(dev_priv, ICL_PORT_PCS_DW1_GRP(phy), val);
>  		}
>  
> -- 
> 2.25.1
>