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SubjectRe: [PATCH] drm/panel: seperate panel power control from panel prepare/unprepare
Hi Jitao.

On Wed, Nov 06, 2019 at 02:40:05PM +0800, Jitao Shi wrote:
> Some dsi panels require the dsi lanes keeping low before panel power
> on. So seperate the panel power control and the communication with panel.
>
> And put the power control in drm_panel_prepare_power and
> drm_panel_unprepare_power. Put the communication with panel in
> drm_panel_prepare and drm_panel_unprepare.
>
> Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>

Panels that requires power before communicating often/always have
some timing constraints. Power need to be applied in XYZ micro seconds
before it is safe to communicate with the panel.

To support this a typical pattern is:

panel_xxx_prepare()
{
// power on the panel using one or a few regulators

// wait until panel is known to be ready

// Communicate with the panel

}

first driver I looked at (panel-feiyang-fy07024di26a30d.c) follows this
pattern.

So we have the timing spelled out in the enable() function
and the sequence is obvious.


What will the benefit be from a separate drm_panel_prepare_power()
function pointer?

Sam


> ---
> drivers/gpu/drm/drm_panel.c | 38 +++++++++++++++++++++++++++++++++++++
> include/drm/drm_panel.h | 17 +++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index 6b0bf42039cf..e57f6385d2cc 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -131,6 +131,24 @@ void drm_panel_detach(struct drm_panel *panel)
> }
> EXPORT_SYMBOL(drm_panel_detach);
>
> +/**
> + * drm_panel_prepare_power - power on a panel's power
> + * @panel: DRM panel
> + *
> + * Calling this function will enable power and deassert any reset signals to
> + * the panel.
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int drm_panel_prepare_power(struct drm_panel *panel)
> +{
> + if (panel && panel->funcs && panel->funcs->prepare_power)
> + return panel->funcs->prepare_power(panel);
> +
> + return panel ? -ENOSYS : -EINVAL;
> +}
> +EXPORT_SYMBOL(drm_panel_prepare_power);
> +
> /**
> * drm_panel_prepare - power on a panel
> * @panel: DRM panel
> @@ -170,6 +188,26 @@ int drm_panel_unprepare(struct drm_panel *panel)
> }
> EXPORT_SYMBOL(drm_panel_unprepare);
>
> +/**
> + * drm_panel_unprepare_power - power off a panel
> + * @panel: DRM panel
> + *
> + * Calling this function will completely power off a panel (assert the panel's
> + * reset, turn off power supplies, ...). After this function has completed, it
> + * is usually no longer possible to communicate with the panel until another
> + * call to drm_panel_prepare_power and drm_panel_prepare().
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int drm_panel_unprepare_power(struct drm_panel *panel)
> +{
> + if (panel && panel->funcs && panel->funcs->unprepare_power)
> + return panel->funcs->unprepare_power(panel);
> +
> + return panel ? -ENOSYS : -EINVAL;
> +}
> +EXPORT_SYMBOL(drm_panel_unprepare_power);
> +
> /**
> * drm_panel_enable - enable a panel
> * @panel: DRM panel
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 624bd15ecfab..0d8c4855405c 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -61,6 +61,13 @@ struct display_timing;
> * the panel. This is the job of the .unprepare() function.
> */
> struct drm_panel_funcs {
> + /**
> + * @prepare_power:
> + *
> + * Turn on panel power.
> + */
> + int (*prepare_power)(struct drm_panel *panel);
> +
> /**
> * @prepare:
> *
> @@ -89,6 +96,13 @@ struct drm_panel_funcs {
> */
> int (*unprepare)(struct drm_panel *panel);
>
> + /**
> + * @unprepare_power:
> + *
> + * Turn off panel_power.
> + */
> + int (*unprepare_power)(struct drm_panel *panel);
> +
> /**
> * @get_modes:
> *
> @@ -155,6 +169,9 @@ void drm_panel_remove(struct drm_panel *panel);
> int drm_panel_attach(struct drm_panel *panel, struct drm_connector *connector);
> void drm_panel_detach(struct drm_panel *panel);
>
> +int drm_panel_prepare_power(struct drm_panel *panel);
> +int drm_panel_unprepare_power(struct drm_panel *panel);
> +
> int drm_panel_prepare(struct drm_panel *panel);
> int drm_panel_unprepare(struct drm_panel *panel);
>
> --
> 2.21.0

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