[PATCH v3 1/1] drm/bridge: ps8640: Rework power state handling
Enric Balletbo i Serra
enric.balletbo at collabora.com
Mon Aug 31 09:45:47 UTC 2020
Hi Bilal,
On 31/8/20 11:32, Bilal Wasim wrote:
>
> Hi Enric,
>
> On Thu, 27 Aug 2020 10:59:11 +0200
> Enric Balletbo i Serra <enric.balletbo at collabora.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 at collabora.com>
>> ---
>>
>> Changes in v3:
>> - Make poweron/poweroff and pre_enable/post_disable reverse one to
>> each other (Sam Ravnborg)
>>
>> Changes in v2:
>> - Use drm_bridge_chain_pre_enable/post_disable() helpers (Sam
>> Ravnborg)
>>
>> drivers/gpu/drm/bridge/parade-ps8640.c | 68
>> ++++++++++++++++++++++---- 1 file changed, 58 insertions(+), 10
>> deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c
>> b/drivers/gpu/drm/bridge/parade-ps8640.c index
>> 9f7b7a9c53c5..7bd0affa057a 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) {
>> @@ -152,10 +155,6 @@ static void ps8640_pre_enable(struct drm_bridge
>> *bridge) goto err_regulators_disable;
>> }
>>
>> - ret = ps8640_bridge_vdo_control(ps_bridge, ENABLE);
>> - if (ret)
>> - goto err_regulators_disable;
>> -
>> /* Switch access edp panel's edid through i2c */
>> ret = i2c_smbus_write_byte_data(client, PAGE2_I2C_BYPASS,
>> I2C_BYPASS_EN);
>> @@ -164,6 +163,8 @@ static void ps8640_pre_enable(struct drm_bridge
>> *bridge) goto err_regulators_disable;
>> }
>>
>> + ps_bridge->powered = true;
>> +
>> return;
>>
>> err_regulators_disable:
>> @@ -171,12 +172,12 @@ 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 +185,28 @@ 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, ENABLE);
>> + 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 +272,34 @@ 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);
>
> Are we sure that pre_enable is always good enough to get the EDID? I
> know that we only have support for ps8640 on the MT8173 SoC which works
> only with pre_enable, but I think a more scalable solution would be to
> call drm_bridge_chain_pre_enable / drm_bridge_chain_enable here, and
> drm_bridge_chain_post_disable / drm_bridge_chain_disable when disabling
> the chain. If this is not a concern and we are sure that pre_enable
> will always work (especially on newer boards), then please ignore my
> comment.
>
Not a drm_bridge API expert, and sometimes I am confused about it, but, from
what I know, I'm pretty sure that we _don't_ want to call drm_bridge_chain_enable().
The call drm_bridge_chain_pre_enable() will end with calling
drm_panel_prepare(), which, as per documentation:
* Calling this function will enable power and deassert any reset signals to
* the panel. After this has completed it is possible to communicate with any
* integrated circuitry via a command bus.
Calling drm_bridge_chain_enable() too will end calling drm_panel_enable(), and,
as per documentation:
* Calling this function will cause the panel display drivers to be turned on
* and the backlight to be enabled. Content will be visible on screen after
* this call completes
Which can trigger a screen flickering and enable more things that what we want.
Reading the EDID should be possible just after a call of drm_bridge_prepare().
Enable the panel should not be required.
Cheers,
Enric
> Other than this, everything looks fine.
>
>>
>> - 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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