Re: [PATCH 2/6] drm/panel: simple: Support panels with HPD where HPD isn't connected

[Sean Paul <sean@poorly.run>]

On Mon, Oct 22, 2018 at 01:46:35PM -0700, Douglas Anderson wrote:
> Some eDP panels that are designed to be always connected to a board
> use their HPD signal to signal that they've finished powering on and
> they're ready to be talked to.
> 
> However, for various reasons it's possible that the HPD signal from
> the panel isn't actually hooked up.  In the case where the HPD isn't
> hooked up you can look at the timing diagram on the panel datasheet
> and insert a delay for the maximum amount of time that the HPD might
> take to come up.
> 
> Let's add support in simple-panel for this concept.
> 
> At the moment we will co-opt the existing "prepare" delay to keep
> track of the delay and we'll use a boolean to specify that a given
> panel should only apply the delay if the "no-hpd" property was
> specified.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/gpu/drm/panel/panel-simple.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 97964f7f2ace..38c646fb55fd 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -63,12 +63,15 @@ struct panel_desc {
>  	 *           turn the display off (no content is visible)
>  	 * @unprepare: the time (in milliseconds) that it takes for the panel
>  	 *             to power itself down completely
> +	 * @prepare_delay_only_if_no_hpd: The prepare delay should only be done
> +	 *                                if we know Hot Plug Detect isn't used.

I think it'd be more clear if we just had a new 'hpd_absent_delay' which is
added to prepare if no_hpd is true.

Sean

>  	 */
>  	struct {
>  		unsigned int prepare;
>  		unsigned int enable;
>  		unsigned int disable;
>  		unsigned int unprepare;
> +		bool prepare_delay_only_if_no_hpd;
>  	} delay;
>  
>  	u32 bus_format;
> @@ -79,6 +82,7 @@ struct panel_simple {
>  	struct drm_panel base;
>  	bool prepared;
>  	bool enabled;
> +	bool no_hpd;
>  
>  	const struct panel_desc *desc;
>  
> @@ -215,7 +219,8 @@ static int panel_simple_prepare(struct drm_panel *panel)
>  
>  	gpiod_set_value_cansleep(p->enable_gpio, 1);
>  
> -	if (p->desc->delay.prepare)
> +	if (p->desc->delay.prepare &&
> +	    (!p->desc->delay.prepare_delay_only_if_no_hpd || p->no_hpd))
>  		msleep(p->desc->delay.prepare);
>  
>  	p->prepared = true;
> @@ -305,6 +310,8 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  	panel->prepared = false;
>  	panel->desc = desc;
>  
> +	panel->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
> +
>  	panel->supply = devm_regulator_get(dev, "power");
>  	if (IS_ERR(panel->supply))
>  		return PTR_ERR(panel->supply);
> -- 
> 2.19.1.568.g152ad8e336-goog
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS