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    SubjectRe: [PATCH 01/22] clk: sunxi-ng: v3s: Make the ISP PLL clock public
    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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