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

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Date:   Mon, 13 Mar 2023 09:06:50 +0100
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Jianhua Lu <lujianhua000@...il.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        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 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. Should
> if (pinfo->desc->num_modes > 1)
> 			mode->type |= DRM_MODE_TYPE_PREFERRED;
> is correct?

I think only a single mode with DRM_MODE_TYPE_PREFERRED is preferred,
so:
if (i == 0)
	mode->type |= DRM_MODE_TYPE_PREFERRED;		

would be the right thing to do.


Neil
>>
>> Konrad
>>>