Date:   Sun, 12 Feb 2023 20:35:33 +0100
From:   =?utf-8?Q?Ond=C5=99ej?= Jirman <megous@megous.com>
To:     Frank Oltmanns <frank@oltmanns.dev>
Cc:     Guido =?utf-8?Q?G=C3=BCnther?= <agx@sigxcpu.org>,
        Purism Kernel Team <kernel@puri.sm>,
        Thierry Reding <thierry.reding@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>,
        Samuel Holland <samuel@sholland.org>
Subject: Re: [PATCH 1/1] drm/panel: st7703: Fix resume of XBD599 panel
Message-ID: <20230212193533.3czfby4id4cpbu2s@core>
Mail-Followup-To: =?utf-8?Q?Ond=C5=99ej?= Jirman <megous@megous.com>,
        Frank Oltmanns <frank@oltmanns.dev>,
        Guido =?utf-8?Q?G=C3=BCnther?= <agx@sigxcpu.org>,
        Purism Kernel Team <kernel@puri.sm>,
        Thierry Reding <thierry.reding@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>, David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>,
        Samuel Holland <samuel@sholland.org>
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Hello,

On Sun, Feb 12, 2023 at 06:52:05PM +0100, Frank Oltmanns wrote:
> Hi Ondřej,
> hi Guido,
> 
> Ondřej, thank you very much for your feedback!
> 
> I have a couple of questions.
> 
> Ondřej Jirman <megi@xff.cz> writes:
> 
> > On Sun, Feb 12, 2023 at 01:08:29PM +0100, Frank Oltmanns wrote:
> >> In contrast to the JH057N panel, the XBD599 panel does not require a 20
> >> msec delay after initialization and exiting sleep mode. Therefore, move
> >> the delay into the already existing device specific initialization
> >> function.
> >>
> >> Also, the timing contraints after entering and exiting sleep mode differ
> >> between the two panels:
> >>  - The JH057N requires a shorter delay than the XDB599 after waking up
> >>    from sleep mode and before enabling the display.
> >>  - The XDB599 requires a delay in order to drain the display of charge,
> >>    which is not required on the JH057N.
> >
> > There’s no difference between the panels here. It’s a controller specified
> > requirement.
> >
> > <https://megous.com/dl/tmp/1ef533ed8a7ce841.png>
> >
> > 60ms used in the driver between sleep out and display on is just
> > incorrect from the datasheet perspective.
> 
> Please let me point you to the discussion you and Guido had ~2.5 years ago:
> <https://lore.kernel.org/all/20200729154809.GA435075@bogon.m.sigxcpu.org/>

Guido references some unspecified datasheet. We only have a st7703 datasheet
to go by, and that requires 120ms and is relevant for both panels.

Also the patch that Guido tested removed a few 20ms delays from the init
sequence for the librem panel. Maybe that broke the init for librem panel and
not the extra few ms after sleep out that the patch added.

> What resonates most with me is the following statement from Guido:
> > > > > Given the amount of ST7703 look alikes i don’t think you can go by the
> > > > > datasheet and hope not to break other panels. The current sleeps cater
> > > > > for the rocktech panel (which suffered from similar issues you describe
> > > > > when we took other parameters) so you need to make those panel specific.
> 
> My takeaway is, that neither panel needed the actual 120 msec wait time. But
> Guido was reluctant to change the timing for the Librem 5 devkit panel. That’s
> why I went for the panel specific implementation.
> 
> Of course, we can revisit that decision. Since I don’t have the Librem
> 5 devkit, I have to kindly ask Guido for advise.
> 
> > You also have to wait 120ms after sleep in (or HW reset) and before shutting
> > down the panel. If you don’t, after a bunch of cycles of this incorrect
> > power up/down sequence the panel will start blinking weirdly, and the incorrect
> > power up/down sequence without delays will not be able to recover it. You’ll
> > have to let the panel sit for 5-10 minutes powered off before it starts to
> > behave itself again.
> >
> > The documentation for sleep in specifies what’s happening during sleep in,
> > and why this delay is necessary after sleep in:
> >
> > <https://megous.com/dl/tmp/2284b9d0f506b9b8.png>
> 
> I read that screenshot, that we need a 120 msec wait after sleep OUT before we
> can send another sleep in (see the “Restriction” row). I can’t seem to find
> the reference to the 120 msec delay after the sleep IN command. I read the
> flow chart at the bottom as informational about the duration of the whole
> procedure that happens after issuing the sleep in command. The only
> restriction is that we can’t issue any command for 5 msec after sleep in was
> issued.

It's at the bottom, sleep in takes 120ms to execute. Part of the execution is
draining the charge from the panel. You can't shutdown power supplies before
sleep in completes, so you need the delay after sleep in and before regulator
powerdown, otherwise the flow chart will not have the time to execute properly,
and the panel will be left in a bad state.

> > So there needs to be 120ms delay after sleep in and after sleep out,
> > regardless of which panel is driven by this controller, to ensure the panel
> > stays operational even when the user is quickly switching it on/off repeatedly.
> >
> > So I don’t think you should be doing panel specific quirks here.
> 
> Maybe. I can only say that without the timings in this patch (i.e. the ones
> from your kernel branch) the display on my pinephone is flickering after the
> first (and every subsequent) time the display is turned off. With your new
> timing everything works great on the pinephone. Guido states that the timings
> in your original patch (i.e. the XDB599 specific timings in this patch) the
> Librem 5 devkit panel doesn’t work.

Adding extra delays after sleep in/before sleep out should not break Librem
panel. Previous patches also changed the powerup sequence to hold the reset
before powerup of the power supplies, and rearranged other delays.

They were made before the problem with the panel discharge was properly
understood.

I suggest just going a bit more conservatively than what I did with my original
patch series, and just make sure there are 120ms delays after sleep out and
before sleep in + extra delay after regulator powerup and don't do anything that
may decrease delays for librem devkit panel. Just adding delays should not break
anything, sine the only timings that have maximums specified in the datasheet
are for power rail voltage rampup times.

(Also some timings during powerup/down may appear to have different needs on
Librem devkit simply because panel driver is not really affecting the
regulators, because they are already powered up due to being referenced by other
drivers/devices, because they are shared. This is a bit tricky to test
properly. It's necessary to test both power sequence cases, where the regulators
are known to be off, and when they are already referenced by other drivers.
On librem devkit, one of them seems to be shared by audio codec and touchscreen,
on pinephone there's less sharing. Easiest way to do that is to unload the
relevant drivers for other devices that share the regulators and check with
debugfs/regulator/regulator_summary that the refcount of lcd regulators)

regards,
	o.

> Do you have a proposal how to proceed without implementing panel specific
> timings?
> 
> Thanks,
>   Frank
> 
> >
> > regards,
> > 	o.
> >
> >> Therefore, introduce panel specific functions for the delays.
> >>
> >> The XDB599 does not require a 20 msec delay between the SETBGP and
> >> SETVCOM commands. Therefore, remove the delay from the device specific
> >> initialization function.
> >>
> >> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
> >> Cc: Ondrej Jirman <megi@xff.cz>
> >> Reported-by: Samuel Holland <samuel@sholland.org>
> >> —
> >>  drivers/gpu/drm/panel/panel-sitronix-st7703.c | 40 ++++++++++++++++—
> >>  1 file changed, 35 insertions(+), 5 deletions(-)
> >>
> >> diff –git a/drivers/gpu/drm/panel/panel-sitronix-st7703.c b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> >> index 6747ca237ced..a149341c4a8b 100644
> >> — a/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> >> +++ b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> >> @@ -66,6 +66,8 @@ struct st7703_panel_desc {
> >>  	unsigned long mode_flags;
> >>  	enum mipi_dsi_pixel_format format;
> >>  	int (*init_sequence)(struct st7703 *ctx);
> >> +	void (*wait_after_sleep_out)(void);
> >> +	void (*drain_charge)(void);
> >>  };
> >>
> >>  static inline struct st7703 *panel_to_st7703(struct drm_panel *panel)
> >> @@ -126,10 +128,24 @@ static int jh057n_init_sequence(struct st7703 *ctx)
> >>  				   0x18, 0x00, 0x09, 0x0E, 0x29, 0x2D, 0x3C, 0x41,
> >>  				   0x37, 0x07, 0x0B, 0x0D, 0x10, 0x11, 0x0F, 0x10,
> >>  				   0x11, 0x18);
> >> +	msleep(20);
> >>
> >>  	return 0;
> >>  }
> >>
> >> +static void jh057n_wait_after_sleep_out(void)
> >> +{
> >> +	/*
> >> +	 * Panel is operational 120 msec after reset, i.e. 60 msec after
> >> +	 * sleep out.
> >> +	 */
> >> +	msleep(60);
> >> +}
> >> +
> >> +static void jh057n_drain_charge(void)
> >> +{
> >> +}
> >> +
> >>  static const struct drm_display_mode jh057n00900_mode = {
> >>  	.hdisplay    = 720,
> >>  	.hsync_start = 720 + 90,
> >> @@ -152,6 +168,8 @@ static const struct st7703_panel_desc jh057n00900_panel_desc = {
> >>  		MIPI_DSI_MODE_VIDEO_BURST | MIPI_DSI_MODE_VIDEO_SYNC_PULSE,
> >>  	.format = MIPI_DSI_FMT_RGB888,
> >>  	.init_sequence = jh057n_init_sequence,
> >> +	.wait_after_sleep_out = jh057n_wait_after_sleep_out,
> >> +	.drain_charge = jh057n_drain_charge,
> >>  };
> >>
> >>  static int xbd599_init_sequence(struct st7703 *ctx)
> >> @@ -273,7 +291,6 @@ static int xbd599_init_sequence(struct st7703 *ctx)
> >>  	mipi_dsi_dcs_write_seq(dsi, ST7703_CMD_SETBGP,
> >>  			       0x07, /* VREF_SEL = 4.2V */
> >>  			       0x07  /* NVREF_SEL = 4.2V */);
> >> -	msleep(20);
> >>
> >>  	mipi_dsi_dcs_write_seq(dsi, ST7703_CMD_SETVCOM,
> >>  			       0x2C, /* VCOMDC_F = -0.67V */
> >> @@ -315,6 +332,18 @@ static int xbd599_init_sequence(struct st7703 *ctx)
> >>  	return 0;
> >>  }
> >>
> >> +static void xbd599_wait_after_sleep_out(void)
> >> +{
> >> +	msleep(120);
> >> +}
> >> +
> >> +static void xbd599_drain_charge(void)
> >> +{
> >> +	/* Drain diplay of charge, to work correctly on next power on. */
> >> +	msleep(120);
> >> +}
> >> +
> >> +
> >>  static const struct drm_display_mode xbd599_mode = {
> >>  	.hdisplay    = 720,
> >>  	.hsync_start = 720 + 40,
> >> @@ -336,6 +365,8 @@ static const struct st7703_panel_desc xbd599_desc = {
> >>  	.mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_SYNC_PULSE,
> >>  	.format = MIPI_DSI_FMT_RGB888,
> >>  	.init_sequence = xbd599_init_sequence,
> >> +	.wait_after_sleep_out = xbd599_wait_after_sleep_out,
> >> +	.drain_charge = xbd599_drain_charge,
> >>  };
> >>
> >>  static int st7703_enable(struct drm_panel *panel)
> >> @@ -350,16 +381,13 @@ static int st7703_enable(struct drm_panel *panel)
> >>  		return ret;
> >>  	}
> >>
> >> -	msleep(20);
> >> -
> >>  	ret = mipi_dsi_dcs_exit_sleep_mode(dsi);
> >>  	if (ret < 0) {
> >>  		dev_err(ctx->dev, “Failed to exit sleep mode: %d\n”, ret);
> >>  		return ret;
> >>  	}
> >>
> >> -	/* Panel is operational 120 msec after reset */
> >> -	msleep(60);
> >> +	ctx->desc->wait_after_sleep_out();
> >>
> >>  	ret = mipi_dsi_dcs_set_display_on(dsi);
> >>  	if (ret)
> >> @@ -384,6 +412,8 @@ static int st7703_disable(struct drm_panel *panel)
> >>  	if (ret < 0)
> >>  		dev_err(ctx->dev, “Failed to enter sleep mode: %d\n”, ret);
> >>
> >> +	ctx->desc->drain_charge();
> >> +
> >>  	return 0;
> >>  }
> >>
> >> –
> >> 2.39.1
> >>