On Mon, Sep 29, 2014 at 01:32:44PM +0200, Geert Uytterhoeven wrote: > Hi Thierry, > > On Mon, Sep 29, 2014 at 12:44 PM, Thierry Reding > <thierry.reding@xxxxxxxxx> wrote: > >> >> You know that you are going to call that for regulator, reset, power > >> >> domains, just as you would have needed to with the proper API, unless > >> >> that with this kind of solution, you would have to modify *every* > >> >> framework that might interact with any resource involved in getting > >> >> simplefb running? > >> > > >> > We have to add handling for every kind of resource either way. Also if > >> > this evolves into a common pattern we can easily wrap it up in a single > >> > function call. > >> > >> disable_all_power_management(), as this is not limited to clocks. > > > > Right. But it isn't all power management either. It just shouldn't turn > > everything unused off. Clocks, regulators, power domains and so on which > > are used can very well be power managed. > > No they can't, as the clock/regulator/PM domain core cannot know if any > of the used ones are also used by a shim driver like simplefb. > Clocks and regulators may be shared. PM domains can contain multiple > hardware blocks. Without more knowledge, the only safe thing is not > disabling anything. Indeed. That's a shame. In the most common case that probably won't matter all that much, given that the real driver can be expected to load within a reasonable amount of time. > >> >> Plus, speaking more specifically about the clocks, that won't prevent > >> >> your clock to be shut down as a side effect of a later clk_disable > >> >> call from another driver. > >> > >> > Furthermore isn't it a bug for a driver to call clk_disable() before a > >> > preceding clk_enable()? There are patches being worked on that will > >> > enable per-user clocks and as I understand it they will specifically > >> > disallow drivers to disable the hardware clock if other drivers are > >> > still keeping them on via their own referenc. > >> > >> Calling clk_disable() preceding clk_enable() is a bug. > >> > >> Calling clk_disable() after clk_enable() will disable the clock (and > >> its parents) > >> if the clock subsystem thinks there are no other users, which is what will > >> happen here. > > > > Right. I'm not sure this is really applicable to this situation, though. > > Yes it is: if all users of a clock/regulator/PM domain are gone, it will > be disabled. Bad luck for simplefb still needing them. Hmm... if all users are gone, then aren't the resources unused again and should therefore be ignored? Thierry
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