linux-kernel - Re: [PATCH 1/2] drm/i915/skl: Don't skip mst encoders in skl_ddi_pll

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Date:	Tue, 02 Feb 2016 17:15:35 +0200
From:	Jani Nikula <jani.nikula@...ux.intel.com>
To:	Lyude <cpaul@...hat.com>, Daniel Vetter <daniel.vetter@...el.com>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, David Airlie <airlied@...hat.com>
Cc:	Rob Clark <rclark@...hat.com>, Adam Jackson <ajax@...hat.com>,
	Lyude <cpaul@...hat.com>
Subject: Re: [PATCH 1/2] drm/i915/skl: Don't skip mst encoders in skl_ddi_pll_select()

On Tue, 02 Feb 2016, Lyude <cpaul@...hat.com> wrote:
> We don't actually check for INTEL_OUTPUT_DP_MST at all in here, as a
> result we skip assigning a DPLL to any DP MST ports, which makes link
> training fail, after which things just keep going downhill from there.

Apparently broken since

commit 82d35437018950c25200051733fb2fbf63cca86c
Author: Satheeshakrishna M <satheeshakrishna.m@...el.com>
Date:   Thu Nov 13 14:55:20 2014 +0000

    drm/i915/skl: Implementation of SKL DPLL programming

> Consequently, this fixes DisplayPort MST causing kernel panics, machine
> check errors, etc. on Skylake.

Please copy-paste some traces for the commit message so it'll be easier
to match bug reports and fixes later on.

BR,
Jani.

>
> Signed-off-by: Lyude <cpaul@...hat.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index e6408e5..54a165b 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1589,7 +1589,8 @@ skl_ddi_pll_select(struct intel_crtc *intel_crtc,
>  			 DPLL_CFGCR2_KDIV(wrpll_params.kdiv) |
>  			 DPLL_CFGCR2_PDIV(wrpll_params.pdiv) |
>  			 wrpll_params.central_freq;
> -	} else if (intel_encoder->type == INTEL_OUTPUT_DISPLAYPORT) {
> +	} else if (intel_encoder->type == INTEL_OUTPUT_DISPLAYPORT ||
> +		   intel_encoder->type == INTEL_OUTPUT_DP_MST) {
>  		switch (crtc_state->port_clock / 2) {
>  		case 81000:
>  			ctrl1 |= DPLL_CTRL1_LINK_RATE(DPLL_CTRL1_LINK_RATE_810, 0);

-- 
Jani Nikula, Intel Open Source Technology Center