Thierry,
On Wed, Apr 23, 2014 at 1:12 PM, Thierry Reding thierry.reding@gmail.com wrote:
On Wed, Apr 23, 2014 at 09:29:15AM +0200, Daniel Vetter wrote:
On Tue, Apr 22, 2014 at 08:06:19PM +0530, Ajay kumar wrote:
Hi Thierry,
On Tue, Apr 22, 2014 at 1:49 PM, Thierry Reding thierry.reding@gmail.com wrote:
On Tue, Apr 22, 2014 at 04:09:11AM +0530, Ajay Kumar wrote:
Most of the panels need an init sequence as mentioned below: -- poweron LCD unit/LCD_EN -- start video data -- poweron LED unit/BL_EN And, a de-init sequence as mentioned below: -- poweroff LED unit/BL_EN -- stop video data -- poweroff LCD unit/LCD_EN With existing callbacks for drm panel, we cannot accomodate such panels, since only two callbacks, i.e "panel_enable" and panel_disable are
supported.
This patch adds: -- "pre_enable" callback which can be called before the actual video data is on, and then call the "enable" callback after the video data is available.
-- "post_disable" callback which can be called after the video data is off, and use "disable" callback to do something before switching off the video data.Now, we can easily map the above scenario as shown below: poweron LCD unit/LCD_EN = "pre_enable" callback poweron LED unit/BL_EN = "enable" callback poweroff LED unit/BL_EN = "disable" callback poweroff LCD unit/LCD_EN = "post_disable" callback
I don't like this. What happens when the next panel comes around that has a yet slightly different requirement? Will we introduce a new pre_pre_enable() and post_post_disable() function then?
As I have already explained, these 2 callbacks are sufficient enough to take care the power up/down sequence for LVDS and eDP panels. And, definitely having just 2 callbacks "enable" and "disable" is not at all sufficient.
I initially thought of using panel_simple_enable from panel-simple driver. But it doesn't go well with case wherein there are 2 regulators(one for LCD and one for LED) a BL_EN signal etc. And, often(Believe me, I have referred to both eDP panel datasheets and LVDS panel datasheets) proper powerup sequence for such panels is as mentioned below:
powerup: -- power up the supply (LCD_VCC). -- start video data. -- enable backlight.
powerdown -- disable backlight. -- stop video data. -- power off the supply (LCD VCC)
For the above cases, if I have to somehow fit in all the required settings, it breaks the sequence and I end up getting glitches during bootup/DPMS.
Also, when the drm_bridge can support pre_enable and post_disable, why not drm_panel provide that both should work in tandem?
Imo this makes sense, especially if we go through with the idea talked about yesterday of creating a drm_bridge to wrap-up a drm_panel with sufficient isolation between all components.
I'm not at all comfortable with these. The names are totally confusing. Next somebody will need to do something after the panel has been enabled and we'll have to introduce .post_enable() and .pre_disable() functions. And worse, what if somebody needs something to be done between .pre_enable() and .enable()? .post_pre_enable()? Where does it end?
According to the above description the only reason why we need this is to avoid visible glitches when the panel is already on, but the video stream hasn't started yet. If that's the only reason why we need this, then perhaps adding a way for a panel to expose the associated backlight would be better?
Actually, we need not expose the entire backlight device. AFAIK, the glitch is caused when you enable BL_EN before there is valid video data. So, one way to mask off the glitch is to follow this sequence: -- power up the panel. -- start video data, (start PWM here or) -- (start PWM here), enable backlight
The problem is that the above scenario cannot be mapped to panel-simple driver. IMO, panel_simple should provide enable/disable controls both for LCD and backlight. something like panel_simple_lcd_enable/panel_simple_led_enable, and panel_simple_lcd_disable/panel_simple_led_disable.
Then we can call panel_simple_lcd_enable before video stream is present, And call panel_simple_led_enable after the video stream is present. In that way we can accomodate majority of LVDS and eDP panels inside panel_simple driver without having to worry about the glitch :)
Thanks and regards, Ajay Kumar