Re: [Freedreno] [PATCH 1/3] drm/msm/mdp5: Configure PP_SYNC_HEIGHT to double the vtotal

[Rob Clark <robdclark@gmail.com>]

On Thu, Apr 8, 2021 at 4:16 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@somainline.org> wrote:
>
>
> Il gio 8 apr 2021, 21:05 Rob Clark <robdclark@gmail.com> ha scritto:
>>
>> 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?
>
>
> Mostly, yes.
>
>>
>> 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
>
>
> Marijn, can you please urgently throw a comment in, reminding that these timers are interacting with TE and send a fast V2?
>

Or just reply on list w/ a comment to smash in, if that is easier

BR,
-R