linux-kernel - Re: [PATCH 1/2] drm: panel-simple: Add simple-panel driver.

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Message-Id: <C2630261-AECD-4357-911F-B0E01E74C74A@theobroma-systems.com>
Date:   Wed, 10 Apr 2019 17:03:44 +0200
From:   Christoph Müllner 
        <christoph.muellner@...obroma-systems.com>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm: panel-simple: Add simple-panel driver.

Hi Heiko,

> On 10.04.2019, at 16:50, Heiko Stübner <heiko@...ech.de> wrote:
> 
> Hi Christoph,
> 
> Am Mittwoch, 10. April 2019, 16:10:44 CEST schrieb Christoph Muellner:
>> On our RK3399-Q7 EVK base board we have the option to connect an arbitrary
>> monitor via DP cable. The actual monitor is therefore not known in advance.
>> This means, we don't have any panel information besides the EDID
>> data from the device itself.
> 
> Just so I understand correctly, you have a real dp-connector wired to
> the Analogix dp-controller, and therefore want to connect actual
> monitors to it.
> 
> So the problem you're trying to work around is probably that the
> rockchip-driver of the analogix controller explictly expects a bridge
> to be present during probe, right?
> 
> I think hacking up the panel-driver is not an ideal approach:
> (1) bridges/panels do expect to stay connected all the time
>    and are meant for devices with actual hard-wired displays with specific
>    power-sequence requirements
> (2) devicetree is expected to describe the real hardware, therefore the
>    dt should not describe one thing while the actual hardware is really
>    different
> 
> So, I guess a more ideal approach could perhaps be to:
> (1) define a "dp-connector" devicetree binding, see
>    Documentation/devicetree/bindings/display/connector/hdmi-connector.txt
>    for a similar one
> (2) steal an idea from drivers/gpu/drm/mediatek/mtk_hdmi.c and check
>    for that new compatible:
> 	if (!of_device_is_compatible(remote, "hdmi-connector")) {
> 		//move bridge handling here
> 	}
> 
>    and modify both the rockchip-part and the generic analogix bridge code
>    to work with the connector declared instead of a panel?

Thank's for you input on this.

Modelling the connector instead of the panel is indeed a better approach,
since we can then also react to connect/disconnect events (after probe).

Thanks,
Christoph

> 
>> The functionality for a 'simple-panel' has been remove a couple
>> of years ago with 81cf32b. This patch brings this feature back.
>> 
>> Signed-off-by: Christoph Muellner <christoph.muellner@...obroma-systems.com>
>> ---
>> drivers/gpu/drm/panel/panel-simple.c | 24 ++++++++++++++++--------
>> 1 file changed, 16 insertions(+), 8 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
>> index 9e8218f6a3f2..1f69283f3e4b 100644
>> --- a/drivers/gpu/drm/panel/panel-simple.c
>> +++ b/drivers/gpu/drm/panel/panel-simple.c
>> @@ -176,7 +176,7 @@ static int panel_simple_disable(struct drm_panel *panel)
>> 		backlight_update_status(p->backlight);
>> 	}
>> 
>> -	if (p->desc->delay.disable)
>> +	if (p->desc && p->desc->delay.disable)
>> 		msleep(p->desc->delay.disable);
>> 
>> 	p->enabled = false;
>> @@ -195,7 +195,7 @@ static int panel_simple_unprepare(struct drm_panel *panel)
>> 
>> 	regulator_disable(p->supply);
>> 
>> -	if (p->desc->delay.unprepare)
>> +	if (p->desc && p->desc->delay.unprepare)
>> 		msleep(p->desc->delay.unprepare);
>> 
>> 	p->prepared = false;
>> @@ -220,11 +220,13 @@ static int panel_simple_prepare(struct drm_panel *panel)
>> 
>> 	gpiod_set_value_cansleep(p->enable_gpio, 1);
>> 
>> -	delay = p->desc->delay.prepare;
>> -	if (p->no_hpd)
>> -		delay += p->desc->delay.hpd_absent_delay;
>> -	if (delay)
>> -		msleep(delay);
>> +	if (p->desc) {
>> +		delay = p->desc->delay.prepare;
>> +		if (p->no_hpd)
>> +			delay += p->desc->delay.hpd_absent_delay;
>> +		if (delay)
>> +			msleep(delay);
>> +	}
>> 
>> 	p->prepared = true;
>> 
>> @@ -238,7 +240,7 @@ static int panel_simple_enable(struct drm_panel *panel)
>> 	if (p->enabled)
>> 		return 0;
>> 
>> -	if (p->desc->delay.enable)
>> +	if (p->desc && p->desc->delay.enable)
>> 		msleep(p->desc->delay.enable);
>> 
>> 	if (p->backlight) {
>> @@ -280,6 +282,9 @@ static int panel_simple_get_timings(struct drm_panel *panel,
>> 	struct panel_simple *p = to_panel_simple(panel);
>> 	unsigned int i;
>> 
>> +	if (!p->desc)
>> +		return 0;
>> +
>> 	if (p->desc->num_timings < num_timings)
>> 		num_timings = p->desc->num_timings;
>> 
>> @@ -2536,6 +2541,9 @@ static const struct panel_desc arm_rtsm = {
>> 
>> static const struct of_device_id platform_of_match[] = {
>> 	{
>> +		.compatible = "simple-panel",
>> +		.data = NULL,
>> +	}, {
>> 		.compatible = "ampire,am-480272h3tmqw-t01h",
>> 		.data = &ampire_am_480272h3tmqw_t01h,
>> 	}, {
>> 
> 
> 
> 
>