Hi, On Mon 13 Sep 21, 09:54, Maxime Ripard wrote: > On Fri, Sep 10, 2021 at 08:41:26PM +0200, Paul Kocialkowski wrote: > > In order to reparent the CSI module clock to the ISP PLL via > > device-tree, export the ISP PLL clock declaration in the public > > device-tree header. > > You use clk_set_rate_exclusive in the ISP driver on the module clock so > it should prevent what you're mentioning from happening. It does, but then it breaks display support entirely (because the DRM driver doesn't use clk_set_rate_exclusive). The bottomline is that using the same PLL for both display and camera easily results in conflicts. > If it doesn't, then clk_set_rate_exclusive has a bug and should be > fixed. > > Either way, using assigned-clock-parents is not a good solution here > either, it only makes sure that this is the case when probe is run. I'm not sure what could provide better guarantees. There is a clock parenting API (in the clock framework) which may, but this implies providing the parent clock to the driver which seems way out of line since this is a platform-specific matter that should certainly not be handled by the driver. I also tried hardcoding the reparenting bit in the CCU driver, but this felt less clean than doing it in device-tree. What do you think? > > Details regarding why the CSI module clock is best parented to the ISP > > PLL are provided in the related commit. > > This is relevant to this commit too and "the related commit" is far too > blurry when you consider the entire Linux git history. Fair enough! Cheers, Paul -- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com
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