linux-kernel - Re: [PATCH] drm/msm/dp: Make it possible to enable the test pattern

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Date:   Mon, 28 Jun 2021 18:07:39 -0700
From:   abhinavk@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: Make it possible to enable the test pattern

On 2021-06-28 17:55, Bjorn Andersson wrote:
> On Mon 28 Jun 19:31 CDT 2021, abhinavk@...eaurora.org wrote:
> 
>> Hi Bjorn
>> 
>> On 2021-06-28 17:22, Bjorn Andersson wrote:
>> > The debugfs interface contains the knobs to make the DisplayPort
>> > controller output a test pattern, unfortunately there's nothing
>> > currently that actually enables the defined test pattern.
>> >
>> > Fixes: de3ee25473ba ("drm/msm/dp: add debugfs nodes for video pattern
>> > tests")
>> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>> 
>> This is not how this debugfs node works. This is meant to be used 
>> while
>> running
>> DP compliance video pattern test.
>> 
>> https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tools/msm_dp_compliance.c
>> 
>> While the compliance test is being run with this msm_dp_compliance app
>> running,
>> it will draw the test pattern when it gets the "test_active" from the
>> driver.
>> 
>> The test pattern which this app draws is as per the requirements of 
>> the
>> compliance test
>> as the test equipment will match the CRC of the pattern which is 
>> drawn.
>> 
>> The API dp_panel_tpg_config() which you are trying to call here draws 
>> the DP
>> test pattern
>> from the DP controller hardware but not the pattern which the 
>> compliance
>> test expects.
>> 
> 
> So clearly not an oversight, but rather me not understanding how to use
> the test pattern.
> 
> You say that I should run msm_dp_compliance while the test is running,
> so how do I run the test?

There are two test patterns with different purposes. The one which the 
msm_dp_compliance
draws is strictly for the DP compliance test and it needs even the DPU 
to draw the frame because
it sets up the display pipeline and just draws the buffer.

That is not what you are looking for here.

So rather than trying to run msm_dp_compliance on your setup, just try 
calling dp_panel_tpg_config().
We typically just call this API, right after the link training is done.
But if you really need a debugfs node for this, you can write up a 
separate debugfs for it
Something like:

echo 1 > dp/tpg/en

Lets not disturb this one.

> 
>> Its just a debug API to call when required during bringup/debug 
>> purposes.
>> 
> 
> Yes, I was trying to isolate the DP code from some misconfiguration in
> the DPU during bringup and with this fix the debugfs interface became
> useful.

> 
> Regards,
> Bjorn
> 
>> Hence this is not the place to call it as it will end up breaking CTS.
>> 
>> Thanks
>> 
>> Abhinav
>> 
>> > ---
>> >  drivers/gpu/drm/msm/dp/dp_debug.c | 2 ++
>> >  1 file changed, 2 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_debug.c
>> > b/drivers/gpu/drm/msm/dp/dp_debug.c
>> > index 2f6247e80e9d..82911af44905 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_debug.c
>> > +++ b/drivers/gpu/drm/msm/dp/dp_debug.c
>> > @@ -305,6 +305,8 @@ static ssize_t dp_test_active_write(struct file
>> > *file,
>> >  				debug->panel->video_test = true;
>> >  			else
>> >  				debug->panel->video_test = false;
>> > +
>> > +			dp_panel_tpg_config(debug->panel, debug->panel->video_test);
>> >  		}
>> >  	}
>> >  	drm_connector_list_iter_end(&conn_iter);