UBUNTU: SAUCE: i915_bpo: drm/i915/skl: Do not enter MST mode during DP probing for DisplayPort MST-enabled hub

From: Gary Wang <gary.c.wang@intel.com>

BugLink: http://bugs.launchpad.net/bugs/1532127

It was found out that DP MST-enabled hub is causing problems of DP link
computation on SKL-U, and need to disable its MST support.

This is a workaround, and need to be fixed further.

References: https://bugs.freedesktop.org/show_bug.cgi?id=91791

Signed-off-by: Gary Wang <gary.c.wang@intel.com>
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
---
 ubuntu/i915/intel_dp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
 mode change 100644 => 100755 ubuntu/i915/intel_dp.c

On Fri, Jan 08, 2016 at 11:48:22AM +0200, Timo Aaltonen wrote:
> From: Gary Wang <gary.c.wang@intel.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1532127
> 
> It was found out that DP MST-enabled hub is causing problems of DP link
> computation on SKL-U, and need to disable its MST support.
> 
> This is a workaround, and need to be fixed further.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=91791
> 
> Signed-off-by: Gary Wang <gary.c.wang@intel.com>
> Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
> ---
>  ubuntu/i915/intel_dp.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>  mode change 100644 => 100755 ubuntu/i915/intel_dp.c
> 
> diff --git a/ubuntu/i915/intel_dp.c b/ubuntu/i915/intel_dp.c
> old mode 100644
> new mode 100755
> index daa1ce2..de89b8f
> --- a/ubuntu/i915/intel_dp.c
> +++ b/ubuntu/i915/intel_dp.c
> @@ -4042,12 +4042,16 @@ intel_dp_probe_oui(struct intel_dp *intel_dp)
>  static bool
>  intel_dp_probe_mst(struct intel_dp *intel_dp)
>  {
> +	struct drm_device *dev = intel_dp_to_dev(intel_dp);
>  	u8 buf[1];
>  
>  	if (!intel_dp->can_mst)
>  		return false;
>  
> -	if (intel_dp->dpcd[DP_DPCD_REV] < 0x12)
> +	//TO-DO, this is workaround for test purpose only on disabling DP 1.2 MST
> +	//SKL-U suffers error from DP data link computation with DP MST enabled.
> +	//fix-BUG https://bugs.freedesktop.org/show_bug.cgi?id=91791
> +	if (intel_dp->dpcd[DP_DPCD_REV] < 0x12 || IS_SKYLAKE(dev))
>  		return false;
>  
>  	if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_MSTM_CAP, buf, 1)) {
> -- 
> 2.5.0
> 
> 
> -- 
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

This is contained to the i915_bpo driver, and should only affect skylake.
Although I *really* hate seeing C++-like comments in kernel code!!! ;-)

Cheers,
--
Luís

Applied to Vivid master-next branch.

Cheers,
--
Luís