From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Date: Mon, 29 Sep 2014 11:32:44 +0000 Subject: Re: [linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code Message-Id: List-Id: References: <53FF1D6C.6090205@redhat.com> <20140829070116.GC13106@ulmo> <20140829141244.GH15297@lukather> <20140829143812.GC31264@ulmo> <20140902092508.GR15297@lukather> <20140927235601.19023.31593@quantum> <20140929080637.GB12506@ulmo> <20140929092301.GC4388@lukather> <20140929101805.GB26008@ulmo> <20140929104454.GD26008@ulmo> In-Reply-To: <20140929104454.GD26008@ulmo> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-arm-kernel@lists.infradead.org Hi Thierry, On Mon, Sep 29, 2014 at 12:44 PM, Thierry Reding 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. >> >> 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. > Either way, if there are other users of a clock then they will just as > likely want to modify the rate at which point simplefb will break just > as badly. BTW, this can also happen for clocks that are properly used. I guess the clock core code does some arbitration to handle such cases. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds