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

[Marek Vasut <marex@denx.de>]

On 4/5/24 11:04 PM, Adam Ford wrote:
> On Fri, Apr 5, 2024 at 3:43 PM Laurent Pinchart
> <laurent.pinchart@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@denx.de>
>>> ---
>>> Cc: Conor Dooley <conor+dt@kernel.org>
>>> Cc: Fabio Estevam <festevam@gmail.com>
>>> Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
>>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>> Cc: Paul Elder <paul.elder@ideasonboard.com>
>>> Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
>>> Cc: Rob Herring <robh@kernel.org>
>>> Cc: Sascha Hauer <s.hauer@pengutronix.de>
>>> Cc: Shawn Guo <shawnguo@kernel.org>
>>> Cc: devicetree@vger.kernel.org
>>> Cc: imx@lists.linux.dev
>>> Cc: linux-arm-kernel@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@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.

MX8MPCEC does indeed read 400 MHz regular, 500 MHz overdrive.

Shall we align both CSI2 ports to 400 MHz ? Currently they are one 500 
MHz and the other 266 MHz .