On Thu, Sep 13, 2012 at 05:21:10PM +0900, Alex Courbot wrote: > On Thursday 13 September 2012 15:50:37 Sascha Hauer wrote: > > On Thu, Sep 13, 2012 at 09:29:20AM +0200, Thierry Reding wrote: > > > On Thu, Sep 13, 2012 at 10:03:27AM +0300, Tomi Valkeinen wrote: > > > > On Thu, 2012-09-13 at 09:00 +0200, Sascha Hauer wrote: > > > > > On Thu, Sep 13, 2012 at 09:54:09AM +0300, Tomi Valkeinen wrote: > > > > > > On Thu, 2012-09-13 at 15:36 +0900, Alex Courbot wrote: > > > > > > > On Thursday 13 September 2012 14:22:57 Tomi Valkeinen wrote: > > > > > > > > However, I fear these board specific things may be quite a bit > > > > > > > > anything, > > > > > > > > so it may well be pwm, gpios and regulators are not enough for > > > > > > > > them. For > > > > > > > > example, there could be an FPGA on the board which requires some > > > > > > > > configuration to accomplish the task at hand. It could be rather > > > > > > > > difficult to handle it with a generic power sequence. > > > > > > > > > > > > > > Right. Note that this framework is supposed to be extended - I > > > > > > > would like to at least add regulator voltage setting, and maybe > > > > > > > even support for clocks and pinmux (but that might be out of > > > > > > > place). > > > > > > > > > > > > Yes, that's one concern of mine... I already can imagine someone > > > > > > suggesting adding conditionals to the power sequence data. Perhaps > > > > > > also > > > > > > direct memory read/writes so you can twiddle registers directly. And > > > > > > so > > > > > > on. Where's the limit what it should contain? Can we soon write full > > > > > > drivers with the DT data? =) > > > > > > > > > > I have this concern aswell, that's why I'm sceptical about this patch > > > > > set. But what are the alternatives? Adding power code to the drivers > > > > > and > > > > > thus adding board specific code to them is backwards. > > > > > > > > As was pointed out in earlier posts in this thread, these are almost > > > > always device specific, not board specific. > > > > > > > > Do you have examples of board specific power sequences or such? > > > > > > It is true that most (perhaps all) power sequences can be associated > > > with a specific device, but if we go and implement drivers for these > > > kinds of devices we will probably end up with loads of variations of > > > the same scheme. > > > > > > Lets take display panels as an example. One of the devices that we build > > > has gone through two generations so far and both are slightly different > > > in how they control the panel backlight: one has an external backlight > > > controller, the other has the display controller built into the panel. > > > However, from the board's perspective the control of the backlight > > > doesn't change, because both devices get the same inputs (an enable pin > > > and a PWM) that map to the same pins on the SoC. > > > > > > This may not be a very good example because the timing isn't relevant, > > > but the basic point is still valid: if we provide a driver for both > > > panel devices, the code will be exactly the same. So we end up having to > > > refactor to avoid code duplication and use the same driver for a number > > > of backlight/panel combinations. Which in itself isn't very bad, but it > > > also means that we'll probably get to see a large number of "generic" > > > drivers which aren't very generic after all. > > > > > > Another problem, which also applies to the case of power-sequences, is > > > that often the panel and backlight are not the same device. > > > > Maybe that is the problem that needs to be addressed? They *are* not the > > same device, still they are handled in a single platform callback (or > > now power sequence). Maybe the amount of combinations dastrically go > > down if we really make them two devices. > > > > Most of our panels have: > > > > - A regulator (or gpio) for turning them on > > > > And the backlights have: > > > > - A regulator (or gpio) for turning them on > > - A PWM for controlling brightness. > > > > The power sequence for the above is clear: Turn on the panel the panel, > > wait until it stabilized and afterwards turn on the backlight. > > Actually the sequence I submitted in this patchset only takes care of the > backlight device (the panel - or LCD - should have its own). The regulator > controls the power supply, the PWM the intensity, and on top of that it also > has an enable GPIO. These 3 resources are exclusively for the LED - the LCD > uses other ones. So as of now it seems that the LCD/backlight separation is > effective and the resources needed are not so uniform across backlights (not > even mentioning the delays). > > The LCD's power sequence is even weirder - VDD must take at least 0.5ms for > going from 10% to 90% of its power, you must wait 400ms after switching it off > before switching it on again, and you should also transmit data for 200ms > before switching the backlight's LED on (using its own sequence). That last > point is interesting since it somehow makes the LCD and LED dependent on each > other - on an unrelated note, this might be something to consider in Laurent's > proposal for a panel framework. Maybe this could be solved by adding a backlight resource type and embedding a reference to the backlight within the panel's power sequence? Thierry
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