linux-kernel - Re: [PATCH v2 2/3] arm64: dts: allwinner: a64: Add A64 CSI controller

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Date:   Fri, 7 Dec 2018 08:47:23 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
Cc:     Jagan Teki <jagan@...rulasolutions.com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-amarula@...rulasolutions.com
Subject: Re: [PATCH v2 2/3] arm64: dts: allwinner: a64: Add A64 CSI controller

On Thu, Dec 06, 2018 at 06:07:59PM +0100, Michael Nazzareno Trimarchi wrote:
> On Thu, Dec 6, 2018 at 4:34 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > On Thu, Dec 06, 2018 at 06:53:05PM +0530, Jagan Teki wrote:
> > > Allwinner A64 CSI controller has similar features as like in
> > > H3, So add support for A64 via H3 fallback.
> > >
> > > Also updated CSI_SCLK to use 300MHz via assigned-clocks, since
> > > the default clock 600MHz seems unable to drive the sensor(ov5640)
> > > to capture the image.
> > >
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > ---
> > > Changes for v2:
> > > - Use CSI_SCLK to 300MHz
> > >
> > >  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 23 +++++++++++++++++++
> > >  1 file changed, 23 insertions(+)
> > >
> > > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > index 384c417cb7a2..d7ab0006ebce 100644
> > > --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > @@ -532,6 +532,12 @@
> > >                       interrupt-controller;
> > >                       #interrupt-cells = <3>;
> > >
> > > +                     csi_pins: csi-pins {
> > > +                             pins = "PE0", "PE2", "PE3", "PE4", "PE5", "PE6",
> > > +                                    "PE7", "PE8", "PE9", "PE10", "PE11";
> > > +                             function = "csi0";
> > > +                     };
> > > +
> > >                       i2c0_pins: i2c0_pins {
> > >                               pins = "PH0", "PH1";
> > >                               function = "i2c0";
> > > @@ -899,6 +905,23 @@
> > >                       status = "disabled";
> > >               };
> > >
> > > +             csi: csi@...0000 {
> > > +                     compatible = "allwinner,sun50i-a64-csi",
> > > +                                  "allwinner,sun8i-h3-csi";
> > > +                     reg = <0x01cb0000 0x1000>;
> > > +                     interrupts = <GIC_SPI 84 IRQ_TYPE_LEVEL_HIGH>;
> > > +                     clocks = <&ccu CLK_BUS_CSI>,
> > > +                              <&ccu CLK_CSI_SCLK>,
> > > +                              <&ccu CLK_DRAM_CSI>;
> > > +                     clock-names = "bus", "mod", "ram";
> > > +                     resets = <&ccu RST_BUS_CSI>;
> > > +                     pinctrl-names = "default";
> > > +                     pinctrl-0 = <&csi_pins>;
> > > +                     assigned-clocks = <&ccu CLK_CSI_SCLK>;
> > > +                     assigned-clock-rates = <300000000>;
> >
> > That should be enforced in the driver.
> >
> 
> We are not really sure what is the best here. Our first idea was to
> put in the board file and then Jagan
> decide to put in dtsi. We don't have enough coverage of camera on this
> CPU and I prefer to stay with this
> minimal change that does not impact the driver.

The thing is that:
  - in this commit log, you're stating that it depends on the sensor,
    which indicates that this would be a board level addition
  - In another patch series, Jagan reported IIRC that it actually
    depends on the resolution, so it doesn't belong in the DT at all
  - And then, you don't even have any guarantee on the clock rate. The
    sole guarantee you have is that when your driver will probe, the
    rate will be close to those 300MHz. That's it. It might completely
    change after the driver has probed, or be rounded to something
    else entirely, who knows.

So really, putting it in the DT is nothing but a hack.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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