On Monday 22 September 2014 13:35:15 Thierry Reding wrote: > On Mon, Sep 22, 2014 at 04:53:22PM +0530, Ajay kumar wrote: > > On Mon, Sep 22, 2014 at 4:11 PM, Thierry Reding wrote: > > > On Mon, Sep 22, 2014 at 02:01:38PM +0530, Ajay kumar wrote: > > >> On Mon, Sep 22, 2014 at 1:40 PM, Thierry Reding wrote: > > >> > On Thu, Sep 18, 2014 at 11:20:40AM +0530, Ajay kumar wrote: > > >> >> On Wed, Sep 17, 2014 at 9:52 PM, Tomi Valkeinen wrote: > > >> >> > On 17/09/14 17:29, Ajay kumar wrote: > > >> >> >> On Wed, Sep 17, 2014 at 5:22 PM, Tomi Valkeinen wrote: > > >> >> >>> On 27/08/14 17:39, Ajay Kumar wrote: > > >> >> >>>> Add documentation for DT properties supported by ps8622/ps8625 > > >> >> >>>> eDP-LVDS converter. > > >> >> >>>> > > >> >> >>>> Signed-off-by: Ajay Kumar <ajaykumar.rs@xxxxxxxxxxx> > > >> >> >>>> --- > > >> >> >>>> > > >> >> >>>> .../devicetree/bindings/video/bridge/ps8622.txt | 20 > > >> >> >>>> ++++++++++++++++++++ 1 file changed, 20 insertions(+) > > >> >> >>>> create mode 100644 > > >> >> >>>> Documentation/devicetree/bindings/video/bridge/ps8622.txt > > >> >> >>>> > > >> >> >>>> diff --git > > >> >> >>>> a/Documentation/devicetree/bindings/video/bridge/ps8622.txt > > >> >> >>>> b/Documentation/devicetree/bindings/video/bridge/ps8622.txt > > >> >> >>>> new file mode 100644 > > >> >> >>>> index 0000000..0ec8172 > > >> >> >>>> --- /dev/null > > >> >> >>>> +++ b/Documentation/devicetree/bindings/video/bridge/ps8622.txt > > >> >> >>>> @@ -0,0 +1,20 @@ > > >> >> >>>> +ps8622-bridge bindings > > >> >> >>>> + > > >> >> >>>> +Required properties: > > >> >> >>>> + - compatible: "parade,ps8622" or "parade,ps8625" > > >> >> >>>> + - reg: first i2c address of the bridge > > >> >> >>>> + - sleep-gpios: OF device-tree gpio specification for PD_ > > >> >> >>>> pin. > > >> >> >>>> + - reset-gpios: OF device-tree gpio specification for RST_ > > >> >> >>>> pin. > > >> >> >>>> + > > >> >> >>>> +Optional properties: > > >> >> >>>> + - lane-count: number of DP lanes to use > > >> >> >>>> + - use-external-pwm: backlight will be controlled by an > > >> >> >>>> external PWM > > >> >> >>> > > >> >> >>> What does this mean? That the backlight support from ps8625 is > > >> >> >>> not used? If so, maybe "disable-pwm" or something? > > >> >> >> > > >> >> >> "use-external-pwm" or "disable-bridge-pwm" would be better. > > >> >> > > > >> >> > Well, the properties are about the bridge. "use-external-pwm" > > >> >> > means that the bridge uses an external PWM, which, if I understood > > >> >> > correctly, is not what the property is about. > > >> >> > > > >> >> > "disable-bridge-pwm" is ok, but the "bridge" there is extra. The > > >> >> > properties are about the bridge, so it's implicit. > > >> >> > > >> >> Ok. I will use "disable-pwm". > > >> > > > >> > Why is this even necessary? According to the datasheet this device > > >> > has circuitry for backlight control. If so, I'd expect it to expose > > >> > either a backlight device or a PWM device. That way unless somebody > > >> > is using the backlight/PWM exposed by the bridge the bridge can > > >> > simply disable PWM. > > >> > > >> The driver does expose a backlight device. > > >> And, the decision(whether to expose a backlight device or not) is made > > >> based on the DT flag "use-external-pwm". > > >> This was discussed before, and you suggested to use the boolean > > >> property, refer to this link: > > >> http://lists.freedesktop.org/archives/dri-devel/2014-July/065048.html > > > > > > I think you misunderstood what I said, or maybe I didn't explain clearly > > > what I meant. If the PS8622 provides a backlight there's nothing wrong > > > with always exposing it. The bridge itself isn't going to be using the > > > backlight anyway. Rather the panel itself should be using the backlight > > > device exposed by PS8622 or some separate backlight device. > > > > > > To illustrate by an example: > > > ps8622: ... { > > > > > > compatible = "parade,ps8622"; > > > ... > > > > > > }; > > > > > > panel { > > > > > > ... > > > backlight = <&ps8622>; > > > ... > > > > > > }; > > > > No, if ps8622 backlight control is used, we need not specify the backlight > > phandle for the panel driver. Somehow, ps8622 internal circuitry keeps > > the bootup glitch free :) > > Backlight control and panel controls can be separate then. > > But they shouldn't. Your panel driver should always be the one to > control backlight. How else is the bridge supposed to know when to turn > backlight on or off? > > > > What you did in v6 of this series was look up a backlight device and > > > then not use it. That seemed unnecessary. Looking at v6 again the reason > > > for getting a phandle to the backlight was so that the device itself did > > > not expose its own backlight controlling circuitry if an external one > > > was being used. But since the bridge has no business controlling the > > > backlight, having the backlight phandle in the bridge is not correct. > > > > > > So I think what you could do in the driver instead is always expose the > > > backlight device. If the panel used a different backlight, the PS8622's > > > internal on simply wouldn't be accessed. It would still be possible to > > > control the backlight in sysfs, but that shouldn't be a problem (only > > > root can access it) > > > > That would be like simple exposing a feature which cannot be used > > by the user, ideally which "should not be" used by the user. > > And it won't be used unless they access the sysfs files directly. There > are a lot of cases where we expose functionality that cannot be > meaningfully used by the user. For example, a GPIO may not be routed to > anything on a board, yet we don't explicitly hide any specific GPIOs > from users. > > > > That said, I have no strong objections to the boolean property if you > > > feel like it's really necessary. > > > > Won't you think having a boolean property for an optional > > feature of the device, is better than all these? > > Like I said, I'm indifferent on the matter. I don't think it's necessary > to hide the backlight device, but if you want to, please feel free to do > so. DT typically use status = "disabled" to disable devices. In this case we don't want to disable the ps8622 completely, but just one of its functions. Maybe a "backlight-status" property could be used for that ? If that's considered too verbose, I would be fine with a "disable-<feature>" boolean property too. > Another alternative would be not to expose it at all and not have the > boolean property since you don't seem to have a way to test it in the > first place (or at least there's no device support upstream where it's > needed). -- Regards, Laurent Pinchart
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