Re: [PATCH 1/2] dt-bindings: media: sun4i-csi: Drop the module clock

[Maxime Ripard <mripard@kernel.org>]

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Hi,

On Thu, Oct 03, 2019 at 11:51:05PM +0800, Chen-Yu Tsai wrote:
> On Thu, Oct 3, 2019 at 11:48 PM Maxime Ripard <mripard@kernel.org> wrote:
> >
> > It turns out that what was thought to be the module clock was actually the
> > clock meant to be used by the sensor, and isn't playing any role with the
> > CSI controller itself. Let's drop that clock from our binding.
> >
> > Fixes: c5e8f4ccd775 ("media: dt-bindings: media: Add Allwinner A10 CSI binding")
> > Reported-by: Chen-Yu Tsai <wens@csie.org>
> > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > ---
> >  .../devicetree/bindings/media/allwinner,sun4i-a10-csi.yaml | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-csi.yaml b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-csi.yaml
> > index 5dd1cf490cd9..d3e423fcb6c2 100644
> > --- a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-csi.yaml
> > +++ b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-csi.yaml
> > @@ -27,14 +27,12 @@ properties:
> >    clocks:
> >      items:
> >        - description: The CSI interface clock
> > -      - description: The CSI module clock
> >        - description: The CSI ISP clock
> >        - description: The CSI DRAM clock
> >
> >    clock-names:
> >      items:
> >        - const: bus
> > -      - const: mod
> >        - const: isp
> >        - const: ram
> >
> > @@ -89,9 +87,8 @@ examples:
> >          compatible = "allwinner,sun7i-a20-csi0";
> >          reg = <0x01c09000 0x1000>;
> >          interrupts = <GIC_SPI 42 IRQ_TYPE_LEVEL_HIGH>;
> > -        clocks = <&ccu CLK_AHB_CSI0>, <&ccu CLK_CSI0>,
> > -                 <&ccu CLK_CSI_SCLK>, <&ccu CLK_DRAM_CSI0>;
> > -        clock-names = "bus", "mod", "isp", "ram";
> > +        clocks = <&ccu CLK_AHB_CSI0>, <&ccu CLK_CSI_SCLK>, <&ccu CLK_DRAM_CSI0>;
> > +        clock-names = "bus", "isp", "ram";
>
> I believe what we thought was the ISP clock is actually the module clock
> for the whole CSI subsystem. So we should still use the module clock entry,
> and remove the ISP entry.

I'm really not sure it is. CSI1 on the A20 (possibly the A10 as well,
I haven't checked), and the one on the A13 don't have any ISP embedded
in the CSI controller.

It makes some difference, because according to the BSP, you can see
that the ISP clock is taken for CSI0:
https://github.com/linux-sunxi/linux-sunxi/blob/sunxi-3.4/drivers/media/video/sun4i_csi/csi0/sun4i_drv_csi.c#L389

While for CSI1, that block is commented out, and the ISP clock never
used:
https://github.com/linux-sunxi/linux-sunxi/blob/sunxi-3.4/drivers/media/video/sun4i_csi/csi1/sun4i_drv_csi.c#L396

So I really believe that the ISP clock is here to feed the ISP block
within the CSI controller if there's any. But it's far from always the
case, as opposed to a module clock for the whole CSI controller that
would be here in both cases.

Maxime

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