Message-ID: <xc4laokjirwetexrcgfxq4kk3wrqn2i7k2kiqe7ivylhgmjw3w@pwwde5mlwxit>
Date: Wed, 26 Jun 2024 12:15:30 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jerome Brunet <jbrunet@...libre.com>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/3] drm/panel: add lincoln lcd197 support

On Wed, Jun 26, 2024 at 11:02:25AM GMT, Jerome Brunet wrote:
> On Wed 26 Jun 2024 at 07:41, Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:
> 
> > On Tue, Jun 25, 2024 at 04:25:50PM GMT, Jerome Brunet wrote:
> >> Add support for the Lincoln LCD197 1080x1920 DSI panel.
> >> 
> >> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> >> ---
> >>  drivers/gpu/drm/panel/Kconfig                |  11 +
> >>  drivers/gpu/drm/panel/Makefile               |   1 +
> >>  drivers/gpu/drm/panel/panel-lincoln-lcd197.c | 333 +++++++++++++++++++
> >>  3 files changed, 345 insertions(+)
> >>  create mode 100644 drivers/gpu/drm/panel/panel-lincoln-lcd197.c
> >> 
> >
> > [...]
> >
> >> +
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xB9, 0xFF, 0x83, 0x99);
> >
> > - Please use lowercase hex instead
> > - Please consider switching to _multi() functions.
> 
> Could you be a bit more specific about these '_multi' function ?
> I've looked at 'drm_mipi_dsi.h' and can't really make what you mean.
> 
> Maybe I'm not looking in the right place.

What is your baseline? Please see commits 966e397e4f60 ("drm/mipi-dsi:
Introduce mipi_dsi_*_write_seq_multi()") and f79d6d28d8fe
("drm/mipi-dsi: wrap more functions for streamline handling") (and
66055636a146 ("drm/mipi-dsi: fix handling of ctx in mipi_dsi_msleep") as
it fixes a mistake in those two).

> 
> >
> >
> >> +	usleep_range(200, 300);
> >
> > This will require new helper msm_dsi_usleep_range(ctx, 200, 300);
> 
> I don't really understand why I would need something else to just sleep
> ? Could you add some context please ?
> 
> Isn't 'msm_' usually something Qcom specific ?

Yes, mipi_dsi_usleep_range(). Mea culpa.

> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xB6, 0x92, 0x92);
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xCC, 0x00);
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xBF, 0x40, 0x41, 0x50, 0x49);
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xC6, 0xFF, 0xF9);
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, 0xC0, 0x25, 0x5A);
> >> +	mipi_dsi_dcs_write_seq(lcd->dsi, MIPI_DCS_SET_ADDRESS_MODE, 0x02);
> >> +
> >> +	err = mipi_dsi_dcs_exit_sleep_mode(lcd->dsi);
> >> +	if (err < 0) {
> >> +		dev_err(panel->dev, "failed to exit sleep mode: %d\n", err);
> >> +		goto poweroff;
> >> +	}
> >> +	msleep(120);
> >> +
> >> +	err = mipi_dsi_dcs_read(lcd->dsi, MIPI_DCS_GET_DISPLAY_ID, display_id, 3);
> >
> > This probably needs new _multi helper too.
> >
> >> +	if (err < 0) {
> >> +		dev_err(panel->dev, "Failed to read display id: %d\n", err);
> >> +	} else {
> >> +		dev_dbg(panel->dev, "Display id: 0x%02x-0x%02x-0x%02x\n",
> >> +			display_id[0], display_id[1], display_id[2]);
> >> +	}
> >> +
> >> +	lcd->prepared = true;
> >
> > Should not be required anymore.
> 
> The whole driver is heavily inspired by what is already in
> drivers/gpu/drm/panel/ and a lot are doing something similar.
> 
> Maybe there has been a change since then and the existing have been
> reworked yet. Would you mind pointing me that change if that is
> the case ?

See d2aacaf07395 ("drm/panel: Check for already prepared/enabled in
drm_panel")

> 
> >
> >> +
> >> +	return 0;
> >> +
> >> +poweroff:
> >> +	gpiod_set_value_cansleep(lcd->enable_gpio, 0);
> >> +	gpiod_set_value_cansleep(lcd->reset_gpio, 1);
> >> +	regulator_disable(lcd->supply);
> >> +
> >> +	return err;
> >> +}
> >> +
> >
> >> +
> >> +static const struct drm_display_mode default_mode = {
> >> +	.clock = 154002,
> >> +	.hdisplay = 1080,
> >> +	.hsync_start = 1080 + 20,
> >> +	.hsync_end = 1080 + 20 + 6,
> >> +	.htotal = 1080 + 204,
> >> +	.vdisplay = 1920,
> >> +	.vsync_start = 1920 + 4,
> >> +	.vsync_end = 1920 + 4 + 4,
> >> +	.vtotal = 1920 + 79,
> >> +	.flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
> >> +};
> >> +
> >> +static int lincoln_lcd197_panel_get_modes(struct drm_panel *panel,
> >> +					  struct drm_connector *connector)
> >> +{
> >> +	struct drm_display_mode *mode;
> >> +
> >> +	mode = drm_mode_duplicate(connector->dev, &default_mode);
> >> +	if (!mode) {
> >> +		dev_err(panel->dev, "failed to add mode %ux%u@%u\n",
> >> +			default_mode.hdisplay, default_mode.vdisplay,
> >> +			drm_mode_vrefresh(&default_mode));
> >> +		return -ENOMEM;
> >> +	}
> >> +
> >> +	drm_mode_set_name(mode);
> >> +	drm_mode_probed_add(connector, mode);
> >> +	connector->display_info.width_mm = 79;
> >> +	connector->display_info.height_mm = 125;
> >
> > drm_connector_helper_get_modes_fixed()
> 
> Thanks for the hint
> 
> >
> >> +
> >> +	return 1;
> >> +}
> >> +
> >
> >
> >> +
> >> +static void lincoln_lcd197_panel_shutdown(struct mipi_dsi_device *dsi)
> >> +{
> >> +	struct lincoln_lcd197_panel *lcd = mipi_dsi_get_drvdata(dsi);
> >> +
> >> +	drm_panel_disable(&lcd->panel);
> >> +	drm_panel_unprepare(&lcd->panel);
> >> +}
> >
> > I think the agreement was that there should be no need for the panel's
> > shutdown, the DRM driver should shutdown the panel.
> 
> I'm happy to drop that if there is such agreement. Again, most panel
> drivers do implement that callback so I just did the same.
> 
> Could you point me to this 'agreement' please, so I can get a better
> understanding of it ? 

Quoting one of commit messages:

    It's the responsibility of a correctly written DRM modeset driver to
    call drm_atomic_helper_shutdown() at shutdown time and that should be
    disabling / unpreparing the panel if needed. Panel drivers shouldn't
    be calling these functions themselves.

I could not describe it better.

-- 
With best wishes
Dmitry

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