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From: Sam Ravnborg <sam@ravnborg.org>
To: Jagan Teki <jagan@amarulasolutions.com>
Cc: David Airlie <airlied@linux.ie>, Sean Paul <sean@poorly.run>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Michael Trimarchi <michael@amarulasolutions.com>,
	linux-amarula@amarulasolutions.com
Subject: Re: [PATCH V7 2/2] drm/panel: Add Sitronix ST7701 panel driver
Date: Sat, 12 Jan 2019 13:00:56 +0100	[thread overview]
Message-ID: <20190112120056.GA7374@ravnborg.org> (raw)
In-Reply-To: <CAMty3ZBUNeFvsHDRmBFUoZG=J+EfQuKtJDOhaezcfEOykhpOeQ@mail.gmail.com>

> >
> > > > > +
> > > > > +     msleep(st7701->sleep_delay);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 0);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 1);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 0);
> > > > No timing constrains here? In prepare there are sleeps intermixed.
> > >
> > > Delay while doing unprare is not needed I suppose.
> >
> > If the purpose is alone to reset the display then a single write '0'
> > should do it I think
> 
> I even tried this just set 0, since prepare is doing a sequence, it
> good behavior to do the reverse during handoff. ie reason I just
> initiated this sequence.
> 
> > And there is a requirement that it must be low for a minimum of 10 us
> > which would be good to have here.
> 
> Sorry, I didn't get this requirement what is this for?
The st7701 will ignore reset pulse shorter than 10 us - see Trw in
table 9 reset timing (page 54).

But as we just assert reset (set it to 0), this timing constraint can be ignored.

> > I aslo found in chapter 9. (page 163 - second line) this statement:
> > "VDDA and VDDI must be powered down with minimum 120msec."
> 
> Yes unprepare is doing the same, it exit from sleep out mode and wait
> for 120msec and do the reset.
> 
> >
> > This is similar to the unprepare delay to be found in simple-panel.c
> > So an unprepare delay seems in order here.
> 
> Look like simple-panel.c is doing delay after reset initiated and
> regulator disabled.


	Sam

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WARNING: multiple messages have this Message-ID (diff)
From: Sam Ravnborg <sam@ravnborg.org>
To: Jagan Teki <jagan@amarulasolutions.com>
Cc: David Airlie <airlied@linux.ie>,
	linux-amarula@amarulasolutions.com,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Michael Trimarchi <michael@amarulasolutions.com>,
	Sean Paul <sean@poorly.run>
Subject: Re: [PATCH V7 2/2] drm/panel: Add Sitronix ST7701 panel driver
Date: Sat, 12 Jan 2019 13:00:56 +0100	[thread overview]
Message-ID: <20190112120056.GA7374@ravnborg.org> (raw)
In-Reply-To: <CAMty3ZBUNeFvsHDRmBFUoZG=J+EfQuKtJDOhaezcfEOykhpOeQ@mail.gmail.com>

> >
> > > > > +
> > > > > +     msleep(st7701->sleep_delay);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 0);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 1);
> > > > > +
> > > > > +     gpiod_set_value(st7701->reset, 0);
> > > > No timing constrains here? In prepare there are sleeps intermixed.
> > >
> > > Delay while doing unprare is not needed I suppose.
> >
> > If the purpose is alone to reset the display then a single write '0'
> > should do it I think
> 
> I even tried this just set 0, since prepare is doing a sequence, it
> good behavior to do the reverse during handoff. ie reason I just
> initiated this sequence.
> 
> > And there is a requirement that it must be low for a minimum of 10 us
> > which would be good to have here.
> 
> Sorry, I didn't get this requirement what is this for?
The st7701 will ignore reset pulse shorter than 10 us - see Trw in
table 9 reset timing (page 54).

But as we just assert reset (set it to 0), this timing constraint can be ignored.

> > I aslo found in chapter 9. (page 163 - second line) this statement:
> > "VDDA and VDDI must be powered down with minimum 120msec."
> 
> Yes unprepare is doing the same, it exit from sleep out mode and wait
> for 120msec and do the reset.
> 
> >
> > This is similar to the unprepare delay to be found in simple-panel.c
> > So an unprepare delay seems in order here.
> 
> Look like simple-panel.c is doing delay after reset initiated and
> regulator disabled.


	Sam


  reply	other threads:[~2019-01-12 12:01 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-11 12:47 [PATCH V7 1/2] dt-bindings: panel: Add Sitronix ST7701 panel documentation Jagan Teki
2019-01-11 12:47 ` Jagan Teki
2019-01-11 12:47 ` [PATCH V7 2/2] drm/panel: Add Sitronix ST7701 panel driver Jagan Teki
2019-01-11 12:47   ` Jagan Teki
2019-01-11 21:19   ` Sam Ravnborg
2019-01-11 21:19     ` Sam Ravnborg
2019-01-11 21:41     ` Noralf Trønnes
2019-01-11 21:41       ` Noralf Trønnes
2019-01-12  3:44     ` Jagan Teki
2019-01-12  3:44       ` Jagan Teki
2019-01-12 10:14       ` Sam Ravnborg
2019-01-12 10:14         ` Sam Ravnborg
2019-01-12 10:46         ` Jagan Teki
2019-01-12 10:46           ` Jagan Teki
2019-01-12 12:00           ` Sam Ravnborg [this message]
2019-01-12 12:00             ` Sam Ravnborg
2019-01-12 13:25             ` Jagan Teki
2019-01-12 13:25               ` Jagan Teki
2019-01-12 15:33               ` Sam Ravnborg
2019-01-12 15:33                 ` Sam Ravnborg
2019-01-12 16:32                 ` Jagan Teki
2019-01-12 16:32                   ` Jagan Teki
2019-01-12 16:53                   ` Sam Ravnborg

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