Re: [PATCH v6 03/10] Documentation: devicetree: Update Samsung FIMC DT binding

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

Hi Sylwester,

On Tuesday 11 March 2014 14:38:37 Sylwester Nawrocki wrote:
> Hi Laurent,
> 
> Thanks for your review.

You're welcome.

> On 11/03/14 13:30, Laurent Pinchart wrote:
> [...]
> 
> >> ---
> >> 
> >>  .../devicetree/bindings/media/samsung-fimc.txt     |   34 +++++++++-----
> >>  1 file changed, 26 insertions(+), 8 deletions(-)
> >> 
> >> diff --git a/Documentation/devicetree/bindings/media/samsung-fimc.txt
> >> b/Documentation/devicetree/bindings/media/samsung-fimc.txt index
> >> 96312f6..dbd4020 100644
> >> --- a/Documentation/devicetree/bindings/media/samsung-fimc.txt
> >> +++ b/Documentation/devicetree/bindings/media/samsung-fimc.txt
> >> @@ -32,6 +32,21 @@ way around.
> >> 
> >>  The 'camera' node must include at least one 'fimc' child node.
> >> 
> >> +Optional properties:
> >> +
> >> +- #clock-cells: from the common clock bindings
> >> (../clock/clock-bindings.txt),
> >> +  must be 1. A clock provider is associated with the 'camera' node and
> >> it should
> >> +  be referenced by external sensors that use clocks provided by the SoC
> >> on
> >> +  CAM_*_CLKOUT pins. The clock specifier cell stores an index of a
> >> clock.
> >> +  The indices are 0, 1 for CAM_A_CLKOUT, CAM_B_CLKOUT clocks
> >> respectively.
> >> +
> >> +- clock-output-names: from the common clock bindings, should contain
> >> names of
> >> +  clocks registered by the camera subsystem corresponding to
> >> CAM_A_CLKOUT,
> >> +  CAM_B_CLKOUT output clocks respectively.
> > 
> > Wouldn't it be better to document the "cam_mclk_a" and "cam_mclk_b" names
> > explicitly ? Or do you expect different names to be used in different DT
> > files ? And as they correspond to the CAM_A_CLKOUT and CAM_B_CLKOUT pins,
> > shouldn't they be named "cam_a_clkout" and "cam_b_clkout" ?
> 
> Basically I could use fixed names for these clocks, I just wanted to keep
> a possibility to override them in dts to avoid any possible clock name
> collisions, rather than keep a list of different names per SoC in the
> driver. Right now fixed names could also be used for all SoCs I'm aware of,
> nevertheless I would prefer to keep the clock-output-names property.
> "cam_a_clkout", "cam_b_clkout" may be indeed better names, I'll change
> that.

OK, variable names are fine with me.

> >> +Note: #clock-cells and clock-output-names are mandatory properties if
> >> external
> >> +image sensor devices reference 'camera' device node as a clock provider.
> >> +
> > 
> > What's the reason not to make them always mandatory ? Backward
> > compatibility only ? If so wouldn't it make sense to document the
> > properties as mandatory from now on, and treating them as optional in the
> > driver for backward compatibility ?
> 
> Yes, it's for backwards compatibility only. It may be a good idea to just
> document them as required, since this is how the device is expected to be
> described in DT from now. I'll just make these a required properties,
> the driver already handles them as optional.

OK.

> >>  'fimc' device nodes
> >>  -------------------
> >> 
> >> @@ -97,8 +112,8 @@ Image sensor nodes
> >> 
> >>  The sensor device nodes should be added to their control bus controller
> >> 
> >> (e.g. I2C0) nodes and linked to a port node in the csis or the
> >> parallel-ports node, using the common video interfaces bindings, defined
> >> in video-interfaces.txt.
> >> -The implementation of this bindings requires clock-frequency property to
> >> be
> >> -present in the sensor device nodes.
> >> +An optional clock-frequency property needs to be present in the sensor
> >> device
> >> +nodes. Default value when this property is not present is 24 MHz.
> > 
> > This bothers me. Having the FIMC driver read the clock-frequence property
> > from the sensor DT nodes feels like a layering violation. Shouldn't the
> > sensor drivers call clk_set_rate() explicitly instead ?
> 
> It is supposed to do so, after this whole patch series. So the camera
> controller driver will not need such properties. What do you think about
> removing this sentence altogether ?

Sure. As the FIMC won't access the clock-frequency property of the sensor 
anymore after this patch series, let's just drop the mention of clock-
frequency.

> >>  Example:
> >> @@ -114,7 +129,7 @@ Example:
> >>  			vddio-supply = <...>;
> >>  			
> >>  			clock-frequency = <24000000>;
> >> 
> >> -			clocks = <...>;
> >> +			clocks = <&camera 1>;
> >> 
> >>  			clock-names = "mclk";
> >>  			
> >>  			port {
> >> 
> >> @@ -135,7 +150,7 @@ Example:
> >>  			vddio-supply = <...>;
> >>  			
> >>  			clock-frequency = <24000000>;
> >> 
> >> -			clocks = <...>;
> >> +			clocks = <&camera 0>;
> >> 
> >>  			clock-names = "mclk";
> >>  			
> >>  			port {
> >> 
> >> @@ -149,12 +164,15 @@ Example:
> >>  	camera {
> >>  	
> >>  		compatible = "samsung,fimc", "simple-bus";
> >> 
> >> -		#address-cells = <1>;
> >> -		#size-cells = <1>;
> >> -		status = "okay";
> >> -
> >> +		clocks = <&clock 132>, <&clock 133>;
> >> +		clock-names = "sclk_cam0", "sclk_cam1";
> > 
> > The documentation mentions that clock-names must contain "sclk_cam0",
> > "sclk_cam1", "pxl_async0", "pxl_async1". Are the last two optional ? If so
> > I think you should clarify the description of the clock-names property.
> > This can be done in a separate patch.
> 
> "pxl_async0", "pxl_async1" are mandatory, I'll add them also into
> this example dts.

OK.

> >> +		#clock-cells = <1>;
> >> +		clock-output-names = "cam_mclk_a", "cam_mclk_b";
> >> 
> >>  		pinctrl-names = "default";
> >>  		pinctrl-0 = <&cam_port_a_clk_active>;
> >> 
> >> +		status = "okay";
> >> +		#address-cells = <1>;
> >> +		#size-cells = <1>;
> >> 
> >>  		/* parallel camera ports */
> >>  		parallel-ports {

-- 
Regards,

Laurent Pinchart