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    SubjectRe: [PATCH v3 1/4] media: dt-bindings: media: i2c: Switch to assigned-clock-rates
    Hi Laurent,

    On Thu, Mar 19, 2020 at 1:04 PM Laurent Pinchart
    <laurent.pinchart@ideasonboard.com> wrote:
    >
    > Hi Maxime,
    >
    > On Thu, Mar 19, 2020 at 01:44:52PM +0100, Maxime Ripard wrote:
    > > On Fri, Mar 13, 2020 at 09:12:31PM +0000, Lad Prabhakar wrote:
    > > > Use assigned-clock-rates to specify the clock rate. Also mark
    > > > clock-frequency property as deprecated.
    > > >
    > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
    > > > ---
    > > > Documentation/devicetree/bindings/media/i2c/ov5645.txt | 5 +++--
    > > > 1 file changed, 3 insertions(+), 2 deletions(-)
    > > >
    > > > diff --git a/Documentation/devicetree/bindings/media/i2c/ov5645.txt b/Documentation/devicetree/bindings/media/i2c/ov5645.txt
    > > > index 72ad992..e62fe82 100644
    > > > --- a/Documentation/devicetree/bindings/media/i2c/ov5645.txt
    > > > +++ b/Documentation/devicetree/bindings/media/i2c/ov5645.txt
    > > > @@ -8,7 +8,7 @@ Required Properties:
    > > > - compatible: Value should be "ovti,ov5645".
    > > > - clocks: Reference to the xclk clock.
    > > > - clock-names: Should be "xclk".
    > > > -- clock-frequency: Frequency of the xclk clock.
    > > > +- clock-frequency (deprecated): Frequency of the xclk clock.
    > > > - enable-gpios: Chip enable GPIO. Polarity is GPIO_ACTIVE_HIGH. This corresponds
    > > > to the hardware pin PWDNB which is physically active low.
    > > > - reset-gpios: Chip reset GPIO. Polarity is GPIO_ACTIVE_LOW. This corresponds to
    > > > @@ -37,7 +37,8 @@ Example:
    > > >
    > > > clocks = <&clks 200>;
    > > > clock-names = "xclk";
    > > > - clock-frequency = <24000000>;
    > > > + assigned-clocks = <&clks 200>;
    > > > + assigned-clock-rates = <24000000>;
    > > >
    > > > vdddo-supply = <&camera_dovdd_1v8>;
    > > > vdda-supply = <&camera_avdd_2v8>;
    > >
    > > clock-frequency is quite different from assigned-clock-rates though,
    > > semantically speaking. clock-frequency is only about what the clock
    > > frequency is, while assigned-clock-rates will change the rate as well,
    > > and you have no idea how long it will last.
    >
    > The driver currently reads the clock-frequency property and then calls
    > clk_set_rate(). I agree tht assigned-clock-rates isn't a panacea, but I
    > think it's less of a hack than what we currently have.
    >
    > As discussed on IRC, maybe the best option in this specific case is to
    > drop clock-frequency and assigned-clok-rates, and call clk_set_rate()
    > with a hardcoded frequency of 24MHz in the driver, as that's the only
    > frequency the driver supports.
    >
    Does this mean any driver which has a fixed clock requirement shouldn't be a
    DT property and should be just handled by the drivers internally ?

    Cheers,
    --Prabhakar

    > > If you want to retrieve that through the clock framework, then just
    > > making clock-frequency optional is enough and falling back to
    > > clk_get_rate on the clocks property already provided is enough.
    >
    > --
    > Regards,
    >
    > Laurent Pinchart
    >
    > _______________________________________________
    > linux-arm-kernel mailing list
    > linux-arm-kernel@lists.infradead.org
    > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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