Re: [PATCH v2 2/6] drm/panel: simple: Support panels with HPD where HPD isn't connected

Sean Paul
2018-10-26T14:41:11Z

On Thu, Oct 25, 2018 at 03:21:30PM -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>

Reviewed-by: Sean Paul <sean@poorly.run>

> ---
>
> Changes in v2:
> - Use "hpd_absent_delay" property instead of a bool + prepare delay
>
> drivers/gpu/drm/panel/panel-simple.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 97964f7f2ace..687fd087b9fc 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -56,6 +56,8 @@ struct panel_desc {
> /**
> * @prepare: the time (in milliseconds) that it takes for the panel to
> * become ready and start receiving video data
> + * @hpd_absent_delay: Add this to the prepare delay if we know Hot
> + * Plug Detect isn't used.
> * @enable: the time (in milliseconds) that it takes for the panel to
> * display the first valid frame after starting to receive
> * video data
> @@ -66,6 +68,7 @@ struct panel_desc {
> */
> struct {
> unsigned int prepare;
> + unsigned int hpd_absent_delay;
> unsigned int enable;
> unsigned int disable;
> unsigned int unprepare;
> @@ -79,6 +82,7 @@ struct panel_simple {
> struct drm_panel base;
> bool prepared;
> bool enabled;
> + bool no_hpd;
>
> const struct panel_desc *desc;
>
> @@ -202,6 +206,7 @@ static int panel_simple_unprepare(struct drm_panel *panel)
> static int panel_simple_prepare(struct drm_panel *panel)
> {
> struct panel_simple *p = to_panel_simple(panel);
> + unsigned int delay;
> int err;
>
> if (p->prepared)
> @@ -215,8 +220,11 @@ static int panel_simple_prepare(struct drm_panel *panel)
>
> gpiod_set_value_cansleep(p->enable_gpio, 1);
>
> - if (p->desc->delay.prepare)
> - msleep(p->desc->delay.prepare);
> + delay = p->desc->delay.prepare;
> + if (p->no_hpd)
> + delay += p->desc->delay.hpd_absent_delay;
> + if (delay)
> + msleep(delay);
>
> p->prepared = true;
>
> @@ -305,6 +313,8 @@ 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