On Mon, Sep 29, 2014 at 01:34:36PM +0200, Maxime Ripard wrote: > On Mon, Sep 29, 2014 at 12:44:57PM +0200, Thierry Reding wrote: > > > >> 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. > > It's actually very easy to do. Have a driver that probes, enables its > clock, fails to probe for any reason, call clk_disable in its exit > path. If there's no other user at that time of this particular clock > tree, it will be shut down. Bam. You just lost your framebuffer. > > Really, it's just that simple, and relying on the fact that some other > user of the same clock tree will always be their is beyond fragile. Perhaps the meaning clk_ignore_unused should be revised, then. What you describe isn't at all what I'd expect from such an option. And it does not match the description in Documentation/kernel-parameters.txt either. > > 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. > > And this can be handled just as well. Register a clock notifier, > refuse any rate change, done. But of course, that would require having > a clock handle. > > Now, how would *you* prevent such a change? Like I said in the other thread. If you have two drivers that use the same clock but need different frequencies you've lost anyway. Thierry
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