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Date:   Fri, 6 Mar 2020 15:16:32 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Alex Riesen <alexander.riesen@cetitec.com>
Cc:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Driver Development <devel@driverdev.osuosl.org>,
        Linux Media <linux-media@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Device Tree <devicetree@vger.kernel.org>,
        Renesas SoC <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH 8/8] arm64: dts: renesas: salvator: add a connection from
 adv748x codec (HDMI input) to the R-Car SoC
Message-ID: <20200306131632.GA4878@pendragon.ideasonboard.com>
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Hi Alex,

On Thu, Mar 05, 2020 at 03:36:28PM +0100, Alex Riesen wrote:
> Geert Uytterhoeven, Mon, Mar 02, 2020 17:13:30 +0100:
> > On Mon, Mar 2, 2020 at 5:09 PM Alex Riesen <alexander.riesen@cetitec.com> wrote:
> > > Geert Uytterhoeven, Mon, Mar 02, 2020 16:32:32 +0100:
> > > >
> > > > The #clock-cells should be in the main video-receiver node.
> > > > Probably there is more than one clock output, so #clock-cells may be 1?
> > >
> > > AFAICS, the device can provide only this one clock line (audio master clock
> > > for I2S output)... I shall re-check, just in case.
> 
> And you're right, of course: the audio output formatting module of the ADV748x
> devices provides a set of clock lines related to the I2S pins: the already
> discussed master clock, left-right channel clock and the serial clock (bit
> clock?).

I don't think we need to model the last two clocks through CCF though,
they're part of the I2S protocol, not clock sources that need to be
explicitly controlled (or queried).

> > > > There is no need for a fixed-clock compatible, nor for clock-frequency
> > > > and clock-output-names.
> > > >
> > > > But most important: this should be documented in the adv748x DT bindings,
> > > > and implemented in the adv748x driver.
> > >
> > > So if the driver is to export that clock for the kernel (like in this case),
> > > it must implement its support?
> > 
> > Exactly.  Unless that pin is hardcoded to output a fixed clock, in which case
> > you can just override the existing audio_clk_c rate.
> 
> Just to try it out (I'll set #clock-cells to 1), I registered a fixed rate
> clock in the driver, added a clock provider:
> 
> adv748x_probe:
> 
>     clk = clk_register_fixed_rate(state->dev,
> 				  "clk-hdmi-i2s-mclk",
> 				  NULL     /* parent_name */,
> 				  0        /* flags */,
> 				  12288000 /* rate */);
>     of_clk_add_provider(state->dev->of_node, of_clk_src_simple_get, clk);
> 
> And removed the audio_clk_c frequency setting. I also replaced the audio_clk_c
> in the list of input clocks of the R-Car-side sound card with the phandle of
> the adv7482 main node:
> 
> salvator-common.dtsi:
> 
>     &i2c4 {
> 	status = "okay";
> 
> 	adv7482_hdmi_decoder: video-receiver@70 {
> 	    #clock-cells = <0>; // to be replaced with <1>
> 	};
>     };
> 
>     &rcar_sound {
> 	clocks = ..., <&adv7482_hdmi_decoder>, ...;
>     };
> 
> As everything continues to work as before, I assume that at least the clock
> dependencies were resolved.

This looks good to me.

> Is there a way to verify that the added input clock is actually used?
> IOW, if its frequency is actually has been programmed into the ssi4 (R-Car
> receiving hardware) registers, and not just a left-over from previuos attempts
> or plain default setting?
> 
> As the ADV748x devices seem to provide also the clocks for video outputs, will
> it make any sense to place the clock definition into the port node?
> Or should all provided clocks be indexed in the main device node?

Those clocks are part of the CSI-2 protocol and also don't need to be
explicitly controlled. As far as I can tell from a quick check of the
ADV7482 documentation, only the I2S MCLK is a general-purpose clock that
needs to be exposed.

-- 
Regards,

Laurent Pinchart