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From:   Rob Clark <robdclark@gmail.com>
Date:   Thu, 8 Apr 2021 12:05:02 -0700
Message-ID: <CAF6AEGuoLgBSZOou1TSb-d2o6tHS-L-E7AQLS5RM4aOogvRG7Q@mail.gmail.com>
Subject: Re: [Freedreno] [PATCH 1/3] drm/msm/mdp5: Configure PP_SYNC_HEIGHT to
 double the vtotal
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@somainline.org>
Cc:     Abhinav Kumar <abhinavk@codeaurora.org>,
        Marijn Suijten <marijn.suijten@somainline.org>,
        phone-devel@vger.kernel.org,
        freedreno <freedreno@lists.freedesktop.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        David Airlie <airlied@linux.ie>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Martin Botka <martin.botka@somainline.org>,
        ~postmarketos/upstreaming@lists.sr.ht,
        Daniel Vetter <daniel@ffwll.ch>, Sean Paul <sean@poorly.run>
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On Wed, Apr 7, 2021 at 12:11 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@somainline.org> wrote:
>
> Il 07/04/21 20:19, abhinavk@codeaurora.org ha scritto:
> > Hi Marijn
> >
> > On 2021-04-06 14:47, Marijn Suijten wrote:
> >> Leaving this at a close-to-maximum register value 0xFFF0 means it takes
> >> very long for the MDSS to generate a software vsync interrupt when the
> >> hardware TE interrupt doesn't arrive.  Configuring this to double the
> >> vtotal (like some downstream kernels) leads to a frame to take at most
> >> twice before the vsync signal, until hardware TE comes up.
> >>
> >> In this case the hardware interrupt responsible for providing this
> >> signal - "disp-te" gpio - is not hooked up to the mdp5 vsync/pp logic at
> >> all.  This solves severe panel update issues observed on at least the
> >> Xperia Loire and Tone series, until said gpio is properly hooked up to
> >> an irq.
> >
> > The reason the CONFIG_HEIGHT was at such a high value is to make sure that
> > we always get the TE only from the panel vsync and not false positives
> > coming
> > from the tear check logic itself.
> >
> > When you say that disp-te gpio is not hooked up, is it something
> > incorrect with
> > the schematic OR panel is not generating the TE correctly?
> >
>
> Sometimes, some panels aren't getting correctly configured by the
> OEM/ODM in the first place: especially when porting devices from
> downstream to upstream, developers often get in a situation in which
> their TE line is either misconfigured or the DriverIC is not configured
> to raise V-Sync interrupts.
> Please remember: some DDICs need a "commands sequence" to enable
> generating the TE interrupts, sometimes this is not standard, and
> sometimes OEMs/ODMs are not even doing that in their downstream code
> (but instead they work around it in creative ways "for reasons", even
> though their DDIC supports indeed sending TE events).
>
> This mostly happens when bringing up devices that have autorefresh
> enabled from the bootloader (when the bootloader sets up the splash
> screen) by using simple-panel as a (hopefully) temporary solution to get
> through the initial stages of porting.
>
> We are not trying to cover cases related to incorrect schematics or
> hardware mistakes here, as the fix for that - as you know - is to just
> fix your hardware.
> What we're trying to do here is to stop freezes and, in some cases,
> lockups, other than false positives making the developer go offroad when
> the platform shows that something is wrong during early porting.
>
> Also, sometimes, some DDICs will not generate TE interrupts when
> expected... in these cases we get a PP timeout and a MDP5 recovery: this
> is totally avoidable if we rely on the 2*vtotal, as we wouldn't get
> through the very time consuming task of recovering the entire MDP.
>
> Of course, if something is wrong in the MDP and the block really needs
> recovery, this "trick" won't save anyone and the recovery will anyway be
> triggered, as the PP-done will anyway timeout.

So, is this (mostly) a workaround due to TE not wired up?  In which
case I think it is ok, but maybe should have a comment about the
interaction with TE?

Currently I have this patch in msm-next-staging but I guess we need to
decide in the next day or so whether to drop it or smash in a comment?

BR,
-R

> >>
> >> Suggested-by: AngeloGioacchino Del Regno
> >> <angelogioacchino.delregno@somainline.org>
> >> Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
> >> Reviewed-by: AngeloGioacchino Del Regno
> >> <angelogioacchino.delregno@somainline.org>
> >> ---
> >>  drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c
> >> b/drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c
> >> index ff2c1d583c79..2d5ac03dbc17 100644
> >> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c
> >> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c
> >> @@ -51,7 +51,7 @@ static int pingpong_tearcheck_setup(struct
> >> drm_encoder *encoder,
> >>
> >>      mdp5_write(mdp5_kms, REG_MDP5_PP_SYNC_CONFIG_VSYNC(pp_id), cfg);
> >>      mdp5_write(mdp5_kms,
> >> -        REG_MDP5_PP_SYNC_CONFIG_HEIGHT(pp_id), 0xfff0);
> >> +        REG_MDP5_PP_SYNC_CONFIG_HEIGHT(pp_id), (2 * mode->vtotal));
> >>      mdp5_write(mdp5_kms,
> >>          REG_MDP5_PP_VSYNC_INIT_VAL(pp_id), mode->vdisplay);
> >>      mdp5_write(mdp5_kms, REG_MDP5_PP_RD_PTR_IRQ(pp_id),
> >> mode->vdisplay + 1);
>