linux-kernel - Re: [PATCH v5 2/2] drm/panel: Add driver for Novatek NT36523

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Date:   Mon, 13 Mar 2023 19:53:30 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Neil Armstrong <neil.armstrong@...aro.org>
Cc:     Jianhua Lu <lujianhua000@...il.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH v5 2/2] drm/panel: Add driver for Novatek NT36523

On Mon, Mar 13, 2023 at 09:06:50AM +0100, Neil Armstrong wrote:
> On 11/03/2023 13:46, Jianhua Lu wrote:
> > On Sat, Mar 11, 2023 at 01:38:52PM +0100, Konrad Dybcio wrote:
> > > 
> > > 
> > > On 11.03.2023 13:32, Jianhua Lu wrote:
> > > > Add a driver for panels using the Novatek NT36523 display driver IC.
> > > > 
> > > > Signed-off-by: Jianhua Lu <lujianhua000@...il.com>
> > > > ---
> > > [...]
> > > 
> > > > +
> > > > +static int nt36523_get_modes(struct drm_panel *panel,
> > > > +			       struct drm_connector *connector)
> > > > +{
> > > > +	struct panel_info *pinfo = to_panel_info(panel);
> > > > +	int i;
> > > > +
> > > > +	for (i = 0; i < pinfo->desc->num_modes; i++) {
> > > > +		const struct drm_display_mode *m = &pinfo->desc->modes[i];
> > > > +		struct drm_display_mode *mode;
> > > > +
> > > > +		mode = drm_mode_duplicate(connector->dev, m);
> > > > +		if (!mode) {
> > > > +			dev_err(panel->dev, "failed to add mode %ux%u@%u\n",
> > > > +				m->hdisplay, m->vdisplay, drm_mode_vrefresh(m));
> > > > +			return -ENOMEM;
> > > > +		}
> > > > +
> > > > +		mode->type = DRM_MODE_TYPE_DRIVER;
> > > > +		if (pinfo->desc->num_modes == 1)
> > > > +			mode->type |= DRM_MODE_TYPE_PREFERRED;
> > > That's not quite correct, as that means "if you have more than one
> > > defined panel mode (say 60Hz and 120 Hz), there will be no preferred one".
> > This piece of code I see in the other panels, so I'm not sure if it is
> > correct.
Jianhua is correct that the same code exists in several places,
and from a quick browse I consider all the cases bogus.

It would be fine if someone volunteered to fix all the panels so we
avoid this bug to creep into more panel drivers.

	Sam