[PATCH] arm64: dts: imx8mp: Align both CSI2 pixel clock

[Adam Ford]

On Fri, Apr 5, 2024 at 3:43 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Marek,
>
> (CC'ing Adam)
>
> Thank you for the patch.
>
> On Fri, Apr 05, 2024 at 10:22:26PM +0200, Marek Vasut wrote:
> > Configure both CSI2 assigned-clock-rates the same way.
> > There does not seem to be any reason for keeping the
> > two CSI2 pixel clock set to different frequencies.
>
> There's an issue when using two cameras concurrently. This has been
> discussed some time ago on the linux-media mailing list, see [1]. Adam
> knows more than I do on this topic.
>
> [1] https://lore.kernel.org/linux-media/CAHCN7x+kymRGO2kxvN2=zLiqRjfTc3hdf3VdNVkWjsW3La0bnA@mail.gmail.com/
>
> > Signed-off-by: Marek Vasut <marex at denx.de>
> > ---
> > Cc: Conor Dooley <conor+dt at kernel.org>
> > Cc: Fabio Estevam <festevam at gmail.com>
> > Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt at linaro.org>
> > Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > Cc: Paul Elder <paul.elder at ideasonboard.com>
> > Cc: Pengutronix Kernel Team <kernel at pengutronix.de>
> > Cc: Rob Herring <robh at kernel.org>
> > Cc: Sascha Hauer <s.hauer at pengutronix.de>
> > Cc: Shawn Guo <shawnguo at kernel.org>
> > Cc: devicetree at vger.kernel.org
> > Cc: imx at lists.linux.dev
> > Cc: linux-arm-kernel at lists.infradead.org
> > ---
> >  arch/arm64/boot/dts/freescale/imx8mp.dtsi | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mp.dtsi b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > index 1bb96e96639f2..2e9ce0c3a9815 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > @@ -1703,7 +1703,7 @@ mipi_csi_1: csi at 32e50000 {
> >                                                 <&clk IMX8MP_CLK_MEDIA_MIPI_PHY1_REF>;
> >                               assigned-clock-parents = <&clk IMX8MP_SYS_PLL2_1000M>,
> >                                                        <&clk IMX8MP_CLK_24M>;
> > -                             assigned-clock-rates = <266000000>;
> > +                             assigned-clock-rates = <500000000>;

I am traveling, so I don't have the technical documents in front of
me, but I beleive this is an over-drive speed, and 400MHz would be the
single clock, standard rate.  I created an imx8mm-overdrive and
imx8mn-overdrive dtsi file to let users who operate in overdrive mode
to update their clocks in one place.

I also think this goes down if the user is running two cameras instead
of one.  I re-read the old thread, and it's coming back to me, but
until I can get settled into my hotel in Germany, I won't have time to
review.  I think the original idea was to use the lowest, conservative
value with the idea that people can tweak their clock settings if
they're only running one and if they are running in over-drive mode.

adam
> >                               power-domains = <&media_blk_ctrl IMX8MP_MEDIABLK_PD_MIPI_CSI2_2>;
> >                               status = "disabled";
> >
>
> --
> Regards,
>
> Laurent Pinchart