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. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
