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Date: Wed, 26 Aug 2020 18:04:14 +0500
From: Bilal Wasim <bwasim.lkml@...il.com>
To: Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc: linux-kernel@...r.kernel.org,
Collabora Kernel ML <kernel@...labora.com>,
matthias.bgg@...il.com, drinkcat@...omium.org, hsinyi@...omium.org,
laurent.pinchart@...asonboard.com, sam@...nborg.org,
Andrzej Hajda <a.hajda@...sung.com>,
Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...ux.ie>,
Jernej Skrabec <jernej.skrabec@...l.net>,
Jonas Karlman <jonas@...boo.se>,
Neil Armstrong <narmstrong@...libre.com>,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 5/5] drm/bridge: ps8640: Rework power state handling
On Wed, 26 Aug 2020 10:15:26 +0200
Enric Balletbo i Serra <enric.balletbo@...labora.com> wrote:
> The get_edid() callback can be triggered anytime by an ioctl, i.e
>
> drm_mode_getconnector (ioctl)
> -> drm_helper_probe_single_connector_modes
> -> drm_bridge_connector_get_modes
> -> ps8640_bridge_get_edid
>
> Actually if the bridge pre_enable() function was not called before
> get_edid(), the driver will not be able to get the EDID properly and
> display will not work until a second get_edid() call is issued and if
> pre_enable() is called before. The side effect of this, for example,
> is that you see anything when `Frecon` starts, neither the splash
> screen, until the graphical session manager starts.
>
> To fix this we need to make sure that all we need is enabled before
> reading the EDID. This means the following:
>
> 1. If get_edid() is called before having the device powered we need to
> power on the device. In such case, the driver will power off again
> the device.
>
> 2. If get_edid() is called after having the device powered, all should
> just work. We added a powered flag in order to avoid recurrent
> calls to ps8640_bridge_poweron() and unneeded delays.
>
> 3. This seems to be specific for this device, but we need to make sure
> the panel is powered on before do a power on cycle on this device.
> Otherwise the device fails to retrieve the EDID.
>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> ---
>
> Changes in v2:
> - Use drm_bridge_chain_pre_enable/post_disable() helpers (Sam
> Ravnborg)
>
> drivers/gpu/drm/bridge/parade-ps8640.c | 64
> +++++++++++++++++++++++--- 1 file changed, 58 insertions(+), 6
> deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c
> b/drivers/gpu/drm/bridge/parade-ps8640.c index
> 9f7b7a9c53c5..c5d76e209bda 100644 ---
> a/drivers/gpu/drm/bridge/parade-ps8640.c +++
> b/drivers/gpu/drm/bridge/parade-ps8640.c @@ -65,6 +65,7 @@ struct
> ps8640 { struct regulator_bulk_data supplies[2];
> struct gpio_desc *gpio_reset;
> struct gpio_desc *gpio_powerdown;
> + bool powered;
> };
>
> static inline struct ps8640 *bridge_to_ps8640(struct drm_bridge *e)
> @@ -91,13 +92,15 @@ static int ps8640_bridge_vdo_control(struct
> ps8640 *ps_bridge, return 0;
> }
>
> -static void ps8640_pre_enable(struct drm_bridge *bridge)
> +static void ps8640_bridge_poweron(struct ps8640 *ps_bridge)
> {
> - struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> struct i2c_client *client = ps_bridge->page[PAGE2_TOP_CNTL];
> unsigned long timeout;
> int ret, status;
>
> + if (ps_bridge->powered)
> + return;
> +
> ret = regulator_bulk_enable(ARRAY_SIZE(ps_bridge->supplies),
> ps_bridge->supplies);
> if (ret < 0) {
> @@ -164,6 +167,8 @@ static void ps8640_pre_enable(struct drm_bridge
> *bridge) goto err_regulators_disable;
> }
>
> + ps_bridge->powered = true;
> +
> return;
>
> err_regulators_disable:
> @@ -171,12 +176,12 @@ static void ps8640_pre_enable(struct drm_bridge
> *bridge) ps_bridge->supplies);
> }
>
> -static void ps8640_post_disable(struct drm_bridge *bridge)
> +static void ps8640_bridge_poweroff(struct ps8640 *ps_bridge)
> {
> - struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> int ret;
>
> - ps8640_bridge_vdo_control(ps_bridge, DISABLE);
> + if (!ps_bridge->powered)
> + return;
>
> gpiod_set_value(ps_bridge->gpio_reset, 1);
> gpiod_set_value(ps_bridge->gpio_powerdown, 1);
> @@ -184,6 +189,28 @@ static void ps8640_post_disable(struct
> drm_bridge *bridge) ps_bridge->supplies);
> if (ret < 0)
> DRM_ERROR("cannot disable regulators %d\n", ret);
> +
> + ps_bridge->powered = false;
> +}
> +
> +static void ps8640_pre_enable(struct drm_bridge *bridge)
> +{
> + struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> + int ret;
> +
> + ps8640_bridge_poweron(ps_bridge);
> +
> + ret = ps8640_bridge_vdo_control(ps_bridge, DISABLE);
> + if (ret < 0)
> + ps8640_bridge_poweroff(ps_bridge);
> +}
> +
> +static void ps8640_post_disable(struct drm_bridge *bridge)
> +{
> + struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> +
> + ps8640_bridge_vdo_control(ps_bridge, DISABLE);
> + ps8640_bridge_poweroff(ps_bridge);
> }
>
> static int ps8640_bridge_attach(struct drm_bridge *bridge,
> @@ -249,9 +276,34 @@ static struct edid
> *ps8640_bridge_get_edid(struct drm_bridge *bridge, struct
> drm_connector *connector) {
> struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> + bool poweroff = !ps_bridge->powered;
> + struct edid *edid;
> +
> + /*
> + * When we end calling get_edid() triggered by an ioctl, i.e
> + *
> + * drm_mode_getconnector (ioctl)
> + * -> drm_helper_probe_single_connector_modes
> + * -> drm_bridge_connector_get_modes
> + * -> ps8640_bridge_get_edid
> + *
> + * We need to make sure that what we need is enabled before
> reading
> + * EDID, for this chip, we need to do a full poweron,
> otherwise it will
> + * fail.
> + */
> + drm_bridge_chain_pre_enable(bridge);
Is it safe for a bridge driver to enable power to other devices in the
bridge? Seems somewhat counter-intuitive, though I understand that the
complete chain needs to be enabled before getting EDID in this case.
Can we consider a more generic solution where the DRM stack enables the
bridge-chain before invoking calls to get EDID based on a DT-binding or
Kconfig option?
Also shouldn't the call to pre_enable be followed by a call to
"drm_bridge_chain_enable"? Similarly we should do both
drm_bridge_chain_post_disable / *_disable when
powering the chips off, right?
>
> - return drm_get_edid(connector,
> + edid = drm_get_edid(connector,
> ps_bridge->page[PAGE0_DP_CNTL]->adapter);
> +
> + /*
> + * If we call the get_edid() function without having enabled
> the chip
> + * before, return the chip to its original power state.
> + */
> + if (poweroff)
> + drm_bridge_chain_post_disable(bridge);
> +
> + return edid;
> }
>
> static const struct drm_bridge_funcs ps8640_bridge_funcs = {
-Bilal
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