On Thu, 2012-09-13 at 09:29 +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. We had something a bit similar in Nokia. First versions had an "independent" backlight controlled via pwm. Later versions had a backlight that is controlled by the panel IP, so it was changed by sending DSI commands to the panel. > 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. So you could > have the same panel with any number of different backlight controllers > or vice-versa any number of different panels with the same backlight > controller. Yes, I think the backlight and the panel should be considered separate devices. Just like, say, a touch screen and a panel may happen to be in the same display module, a backlight and a panel can be in the same display module. They are still separate, independent things, although they are, of course, used together. Tomi
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