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@xxxxxxxxxxxx>
> ---
>
> 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
