Re: (EXT) [PATCH] arm64: dts: imx8mp: Add CSIS DT nodes

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Alexander,

On Fri, Jun 17, 2022 at 08:43:53AM +0200, Alexander Stein wrote:
> Hello Laurent,
> 
> thanks for ths and the other MIPI CSI-2 related patches.
> 
> Am Donnerstag, 16. Juni 2022, 18:16:43 CEST schrieb Laurent Pinchart:
> > Add DT nodes for the two CSI-2 receivers of the i.MX8MP.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > ---
> > This patch depends on the DT bindings submitted in [1], for which I plan
> > to submit a pull request for v5.20.
> > 
> > [1] https://lore.kernel.org/linux-media/83e27382-6f97-015f-2ee1-f43820967093@linaro.org/T/#u
> > ---
> >  arch/arm64/boot/dts/freescale/imx8mp.dtsi | 60 +++++++++++++++++++++++
> >  1 file changed, 60 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > b/arch/arm64/boot/dts/freescale/imx8mp.dtsi index
> > d9542dfff83f..c8ed206b7f41 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
> > @@ -1063,6 +1063,66 @@ media_blk_ctrl: blk-ctrl@32ec0000 {
> >  				#power-domain-cells = <1>;
> >  			};
> > 
> > +			mipi_csi_0: csi@32e40000 {
> > +				compatible = "fsl,imx8mp-mipi-csi2", "fsl,imx8mm-mipi-csi2";
> > +				reg = <0x32e40000 0x10000>;
> > +				interrupts = <GIC_SPI 17 IRQ_TYPE_LEVEL_HIGH>;
> > +				clock-frequency = <500000000>;
> 
> According to datasheet (IMX8MPIEC Rev 1, Table 1, Subsystem "MIPI Interface") 
> "MIPI CSI1" supports up to 500MHz only in single camera use and overdrive 
> mode. In normal mode only 400MHz are supported. For dual camera usage only up 
> to 266MHz is supported.

I wasn't aware of that, thank you for the information.

> Apparently this is when using ISP, things might be 
> different when using ISI.

Table 13 documents the maximum frequencies of clocks
MEDIA_CAM1_PIX_CLK_ROOT and MEDIA_CAM2_PIX_CLK_ROOT to be 400/500MHz
(normal/overdrive) and 277/277MHz respectively, so I'd say this affects
the ISI too. I wonder what causes the 266MHz constraint for dual camera
mode.

There's also a constraint of at most 375 MPixel/s aggregate performance
for the two ISP instances, but I don't know if that's due to the memory
bandwidth, or if it is on the input side in which case it may include
blanking and translate directly to clock frequencies. If I had to guess,
I'd say the former.

> I'm hesitating specifying the overdrive mode 
> frequency here. Most users, most probably using normal mode, would have 
> requiring them to adjust this.
> For dual camera this is even as low as 266MHz, but IMHO this is a special 
> case.

I agree, we should at least lower the frequency to 400MHz here. Given
that the frequency limit depends on whether one or two cameras are used,
I'm actually tempted to either specify the worst case (2x 266MHz), or
even drop the clock-frequency completely, forcing users to think about
what they need. The driver however silently falls back to a default
frequency of 166MHz when the property isn't set, so developers won't
necessarily immediately notice that something is wrong, or why.

Should I specify 400 MHz and 266 MHz here, or go for the safer option of
266 MHz and 266 MHz ?

> > +				clocks = <&clk IMX8MP_CLK_MEDIA_APB_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_CAM1_PIX_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_MIPI_PHY1_REF_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_AXI_ROOT>;
> > +				clock-names = "pclk", "wrap", "phy", "axi";
> > +				assigned-clocks = <&clk IMX8MP_CLK_MEDIA_CAM1_PIX>;
> > +				assigned-clock-parents = <&clk IMX8MP_SYS_PLL2_1000M>;
> > +				assigned-clock-rates = <500000000>;
> > +				power-domains = <&media_blk_ctrl IMX8MP_MEDIABLK_PD_MIPI_CSI2_1>;
> > +				status = "disabled";
> > +
> > +				ports {
> > +					#address-cells = <1>;
> > +					#size-cells = <0>;
> > +
> > +					port@0 {
> > +						reg = <0>;
> > +					};
> > +
> > +					port@1 {
> > +						reg = <1>;
> > +					};
> > +				};
> > +			};
> > +
> > +			mipi_csi_1: csi@32e50000 {
> > +				compatible = "fsl,imx8mp-mipi-csi2", "fsl,imx8mm-mipi-csi2";
> > +				reg = <0x32e50000 0x10000>;
> > +				interrupts = <GIC_SPI 80 IRQ_TYPE_LEVEL_HIGH>;
> > +				clock-frequency = <266000000>;
> 
> For single camera usage this can even go as high as 277MHz. 266MHz is only for 
> dual camera use.
> 
> > +				clocks = <&clk IMX8MP_CLK_MEDIA_APB_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_CAM2_PIX_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_MIPI_PHY1_REF_ROOT>,
> > +					 <&clk IMX8MP_CLK_MEDIA_AXI_ROOT>;
> > +				clock-names = "pclk", "wrap", "phy", "axi";
> > +				assigned-clocks = <&clk IMX8MP_CLK_MEDIA_CAM2_PIX>;
> > +				assigned-clock-parents = <&clk IMX8MP_SYS_PLL2_1000M>;
> > +				assigned-clock-rates = <266000000>;
> > +				power-domains = <&media_blk_ctrl IMX8MP_MEDIABLK_PD_MIPI_CSI2_2>;
> > +				status = "disabled";
> > +
> > +				ports {
> > +					#address-cells = <1>;
> > +					#size-cells = <0>;
> > +
> > +					port@0 {
> > +						reg = <0>;
> > +					};
> > +
> > +					port@1 {
> > +						reg = <1>;
> > +					};
> > +				};
> > +			};
> > +
> >  			hsio_blk_ctrl: blk-ctrl@32f10000 {
> >  				compatible = "fsl,imx8mp-hsio-blk-ctrl", "syscon";
> >  				reg = <0x32f10000 0x24>;
> > 
> > base-commit: b13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3

-- 
Regards,

Laurent Pinchart

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