Re: [PATCH 1/4] drm/i915: read dpcd 0 - 12 & link_status always

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 02 Sep 2015, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Tue, Sep 01, 2015 at 01:16:49PM +0300, Jani Nikula wrote:
>> On Thu, 27 Aug 2015, Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> wrote:
>> > From: "Thulasimani,Sivakumar" <sivakumar.thulasimani@intel.com>
>> >
>> > Compliance requires the driver to read dpcd register 0 to 12 and
>> > registers 0x200 to 0x205 to be read always.
>> > Current code performs dpcd read for short pulse interrupts only
>> > if the sink is enabled. This patch forces read for link status
>> > and registers 0 to 12.
>> 
>> While this seems a bit silly from the driver perspective, I don't see it
>> doing much harm either.
>
> I don't think this is silly, but fixing it like this might be - currently
> we don't do _any_ detection of sink ports, so if you have a hub with two
> outputs and then plug in another one and plug out the first userspace
> won't reprobe. So probably what we should be doing is not just read the
> dpcd, but actually look at it, figure out whether something has changed
> and make sure we send out the uevent even if the hpd line stays unchanged
> on short pulses to make userspace aware of the changes.
>
> Punting on this for now since I suspect there's a bigger story to be had
> here ...

Well, I'll bet this would be a preliminary step for that anyway.

BR,
Jani.


> -Daniel
>
>> 
>> Note that We do read dpcd 0 to 14 no matter what the spec says.
>> 
>> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
>> 
>> >
>> > Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/intel_dp.c |   12 ++++++------
>> >  1 file changed, 6 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> > index 8a66a44..76561e0 100644
>> > --- a/drivers/gpu/drm/i915/intel_dp.c
>> > +++ b/drivers/gpu/drm/i915/intel_dp.c
>> > @@ -4374,12 +4374,6 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>> >  
>> >  	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>> >  
>> > -	if (!intel_encoder->base.crtc)
>> > -		return;
>> > -
>> > -	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>> > -		return;
>> > -
>> >  	/* Try to read receiver status if the link appears to be up */
>> >  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
>> >  		return;
>> > @@ -4390,6 +4384,12 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>> >  		return;
>> >  	}
>> >  
>> > +	if (!intel_encoder->base.crtc)
>> > +		return;
>> > +
>> > +	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>> > +		return;
>> > +
>> >  	/* Try to read the source of the interrupt */
>> >  	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
>> >  	    intel_dp_get_sink_irq(intel_dp, &sink_irq_vector)) {
>> > -- 
>> > 1.7.9.5
>> >
>> 
>> -- 
>> Jani Nikula, Intel Open Source Technology Center
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Jani Nikula, Intel Open Source Technology Center
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