Re: [PATCH v2 5/5] drm/bridge: ps8640: Rework power state handling

[Enric Balletbo i Serra <enric.balletbo@collabora.com>]

Hi Sam,

Thanks for your comments.

On 26/8/20 20:46, Sam Ravnborg wrote:
> Hi Enric.
> 
> On Wed, Aug 26, 2020 at 10:15:26AM +0200, Enric Balletbo i Serra 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@collabora.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);
>> +}
> 
> The impleimentation of ps8640_bridge_poweron() versus
> ps8640_bridge_poweroff() is confusing.
> 
> ps8640_bridge_poweron() includes ps8640_bridge_vdo_control(.., ENABLE),
> but ps8640_bridge_poweroff() does not include
> ps8640_bridge_vdo_control(..., DISABLE).
> 
> This is inconsistent and confusing. At least it was for me when
> reviewing. Can this be improved - or maybe just use naming that does not
> indicate they are the reverse of each other?
> 

Right, I think I can implement reverse of each other. So I'll send an updated
series.

Thanks,
 Enric

>> +
>> +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);
>>  
>> -	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;
>>  }
> 
> The use of drm_bridge_chain_pre_enable() and
> drm_bridge_chain_post_disable() was exactly what I was asking for -
> looks good.
> 
> I have not really considered the idea from Balil that we should provide
> better infrastructure support powering on the bridge chain when reading
> the edid. Maybe an idea for later?
> 
> 	Sam
> 
> 
> 
>>  
>>  static const struct drm_bridge_funcs ps8640_bridge_funcs = {
>> -- 
>> 2.28.0
> 
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