Re: [PATCH 2/7] drm/i915/dp: Don't switch to idle pattern before disable on pre-hsw

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

On Thu, Jul 10, 2025 at 11:17:13PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> For some reason we are switching over to the idle pattern before
> disabling the DP port on pre-hsw. AFAICS this has never been part
> of the documented sequence (and on hsw+ the spec explicitly says
> not to do this). Get rid of it.
> 
> The code goes all the way back to commit 5eb08b69f510 ("drm/i915: enable
> DisplayPort support on IGDNG"), and it was accompanied by a 17ms delay
> which got changed to vbl wait in commit ab527efc2fea ("drm/i915: use
> wait_for_vblank instead of msleep(17)"), and was later completely removed
> in  commit 93c9c19b3d25 ("drm/i915: remove unexplained vblank wait in
> the DP off code").
> 
> Smoke tested on g4x/snb/chv.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Matches the spec on SNB/IVB at least, I can't see a requirement to set
idle patterns before the 'Disable port' step there, based on that:

Reviewed-by: Imre Deak <imre.deak@intel.com>

> ---
>  drivers/gpu/drm/i915/display/g4x_dp.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/g4x_dp.c b/drivers/gpu/drm/i915/display/g4x_dp.c
> index 87f6b9602b16..b54edf0d1c23 100644
> --- a/drivers/gpu/drm/i915/display/g4x_dp.c
> +++ b/drivers/gpu/drm/i915/display/g4x_dp.c
> @@ -424,17 +424,6 @@ intel_dp_link_down(struct intel_encoder *encoder,
>  
>  	drm_dbg_kms(display->drm, "\n");
>  
> -	if ((display->platform.ivybridge && port == PORT_A) ||
> -	    (HAS_PCH_CPT(display) && port != PORT_A)) {
> -		intel_dp->DP &= ~DP_LINK_TRAIN_MASK_CPT;
> -		intel_dp->DP |= DP_LINK_TRAIN_PAT_IDLE_CPT;
> -	} else {
> -		intel_dp->DP &= ~DP_LINK_TRAIN_MASK;
> -		intel_dp->DP |= DP_LINK_TRAIN_PAT_IDLE;
> -	}
> -	intel_de_write(display, intel_dp->output_reg, intel_dp->DP);
> -	intel_de_posting_read(display, intel_dp->output_reg);
> -
>  	intel_dp->DP &= ~DP_PORT_EN;
>  	intel_de_write(display, intel_dp->output_reg, intel_dp->DP);
>  	intel_de_posting_read(display, intel_dp->output_reg);
> -- 
> 2.49.0
>