On Mon, Sep 29, 2014 at 05:57:18PM +0200, Maxime Ripard wrote: > On Mon, Sep 29, 2014 at 03:54:00PM +0200, Thierry Reding wrote: > > 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. > > Well, it never says that it also prevent them from being disabled > later on. But it's true it's not very explicit. It says: Keep all clocks already enabled by bootloader on, even if no driver has claimed them. ... There's no "until" or anything there, so I interpret that as indefinitely. > > > > 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. > > Except that the driver that has the most logic (ie not simplefb) will > have a way to recover and deal with that. You're making an assumption here. Why would the driver have such logic if nothing ever prevented it from setting the rate properly before. > But sure, you can still try to point new issues, get an obvious and > robust solution, and then discard the issue when the solution doesn't > go your way... And you've already proven that you're completely unwilling to even consider any other solution than what was originally proposed, so I really don't see how discussing this further with you is going to be productive. Thierry
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