Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
MIME-Version: 1.0
References: <20231007060639.725350-1-yangcong5@huaqin.corp-partner.google.com>
 <20231007060639.725350-3-yangcong5@huaqin.corp-partner.google.com>
 <CAD=FV=W3ef3vWrWRDPKgeUjcapEticj4=EWdC-bOb=ph0DShsA@mail.gmail.com> <CAHwB_N+=h8-5H6SM8REAge19SgLvrZD=drAP83QnSuuqB5gN8A@mail.gmail.com>
In-Reply-To: <CAHwB_N+=h8-5H6SM8REAge19SgLvrZD=drAP83QnSuuqB5gN8A@mail.gmail.com>
From:   Doug Anderson <dianders@google.com>
Date:   Tue, 10 Oct 2023 12:11:30 -0700
Message-ID: <CAD=FV=XtqPJ77dx8uRb0=tMvC3CvgH5X+7mUJeXgcG228kZfUg@mail.gmail.com>
Subject: Re: [v1 2/2] drm/panel: ili9882t: Avoid blurred screen from fast sleep
To:     cong yang <yangcong5@huaqin.corp-partner.google.com>
Cc:     sam@ravnborg.org, neil.armstrong@linaro.org, daniel@ffwll.ch,
        hsinyi@google.com, linus.walleij@linaro.org, swboyd@chromium.org,
        airlied@gmail.com, dri-devel@lists.freedesktop.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Hi,

On Tue, Oct 10, 2023 at 4:36=E2=80=AFAM cong yang
<yangcong5@huaqin.corp-partner.google.com> wrote:
>
> Hi,
>
> On Tue, Oct 10, 2023 at 4:44=E2=80=AFAM Doug Anderson <dianders@google.co=
m> wrote:
> >
> > Hi,
> >
> > On Fri, Oct 6, 2023 at 11:07=E2=80=AFPM Cong Yang
> > <yangcong5@huaqin.corp-partner.google.com> wrote:
> > >
> > > At present, we have found that there may be a problem of blurred
> > > screen during fast sleep/resume. The direct cause of the blurred
> > > screen is that the IC does not receive 0x28/0x10. Because of the
> > > particularity of the IC, before the panel enters sleep hid must
> > > stop scanning, i2c_hid_core_suspend before ili9882t_disable.
> > > This doesn't look very spec-compliant.
> >
> > Presumably you could be more spec compliant if we used
> > "panel_follower" in this case? Would that be a better solution?
>
> In the "panel_follower" solution, the phenomenon is the same.
> The current order is
> ili9882t_disable=3D>i2c_hid_core_suspend=3D>elan_i2c_hid_power_down=3D>il=
i9882t_unprepare,
> ili9882t need touchpanel stop scanning,i2c_hid_core_suspend before
> ili9882t_disable.

Ugh, that's unfortunate. Though is there a reason why you couldn't
just move the `ili9882t_enter_sleep_mode()` to `ili9882t_unprepare()`?
That seems like it should be OK and even perhaps makes it more
symmetric with thue enable?


> > > @@ -507,7 +526,7 @@ static int ili9882t_prepare(struct drm_panel *pan=
el)
> > >         gpiod_set_value(ili->enable_gpio, 1);
> > >         usleep_range(1000, 2000);
> > >         gpiod_set_value(ili->enable_gpio, 0);
> > > -       usleep_range(1000, 2000);
> > > +       usleep_range(40000, 50000);
> >
> > nit: use 40000, 41000 instead of 40000, 50000. Linux almost always
> > uses the longer delay, so that'll save ~9 ms. The only reason for the
> > range is to optimize kernel wakeups which is really not a concern
> > here.
>
> We need 50ms delay to meet the requirement.

I'll respond to your v2, but if you need 50 ms then your current delay is w=
rong.


-Doug