linux-kernel - Re: [PATCH v3 01/24] [media] dt-bindings: Add bindings for i.MX media driver

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Message-ID: <1484568579.8415.91.camel@pengutronix.de>
Date:   Mon, 16 Jan 2017 13:09:39 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
        linux@...linux.org.uk, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v3 01/24] [media] dt-bindings: Add bindings for i.MX
 media driver

On Fri, 2017-01-13 at 11:03 -0800, Steve Longerbeam wrote:
> 
> On 01/13/2017 03:55 AM, Philipp Zabel wrote:
> > Am Freitag, den 06.01.2017, 18:11 -0800 schrieb Steve Longerbeam:
> >> Add bindings documentation for the i.MX media driver.
> >>
> >> Signed-off-by: Steve Longerbeam <steve_longerbeam@...tor.com>
> >> ---
> >>   Documentation/devicetree/bindings/media/imx.txt | 57 +++++++++++++++++++++++++
> >>   1 file changed, 57 insertions(+)
> >>   create mode 100644 Documentation/devicetree/bindings/media/imx.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/media/imx.txt b/Documentation/devicetree/bindings/media/imx.txt
> >> new file mode 100644
> >> index 0000000..254b64a
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/media/imx.txt
> >> @@ -0,0 +1,57 @@
> >> +Freescale i.MX Media Video Devices
> >> +
> >> +Video Media Controller node
> >> +---------------------------
> >> +
> >> +This is the parent media controller node for video capture support.
> >> +
> >> +Required properties:
> >> +- compatible : "fsl,imx-media";
> > Would you be opposed to calling this "capture-subsystem" instead of
> > "imx-media"? We already use "fsl,imx-display-subsystem" and
> > "fsl,imx-gpu-subsystem" for the display and GPU compound devices.
> 
> sure. Some pie-in-the-sky day when DRM and media are unified,
> there could be a single device that handles them all,

Indeed :)

>  but for now
> I'm fine with "fsl,capture-subsystem".

Actually, I meant fsl,imx-capture-subsystem. fsl,imx-media-subsystem
would be fine, too. Either way, I'll be happy if it looks similar to the
other two.

[...]
> > This is a clever method to get better frame timestamps. Too bad about
> > the routing requirements. Can this be used on Nitrogen6X?
> 
> Absolutely, this support just needs use of the input-capture channels in the
> imx GPT. I still need to submit the patch to the imx-gpt driver that adds an
> input capture API, so at this point fsl,input-capture-channel has no effect,
> but it does work (tested on SabreAuto).

Nice.

[...]
> >> +Required properties:
> >> +- compatible	: "fsl,imx6-mipi-csi2";
> > I think this should get an additional "snps,dw-mipi-csi2" compatible,
> > since the only i.MX6 specific part is the bolted-on IPU2CSI gasket.
> 
> right, minus the gasket it's a Synopsys core. I'll add that compatible flag.
> Or should wait until the day this subdev is exported for general use, after
> pulling out the gasket specifics?

It can be added right away.

> >> +- reg           : physical base address and length of the register set;
> >> +- clocks	: the MIPI CSI-2 receiver requires three clocks: hsi_tx
> >> +                  (the DPHY clock), video_27m, and eim_sel;
> > Note that hsi_tx is incorrectly named. CCGR3[CG8] just happens to be the
> > shared gate bit that gates the HSI clocks as well as the MIPI
> > "ac_clk_125m", "cfg_clk", "ips_clk", and "pll_refclk" inputs to the mipi
> > csi-2 core, but we are missing shared gate clocks in the clock tree for
> > these.
> 
> Yes, so many clocks for the MIPI core. Why so many? I would think
> there would need to be at most three: a clock for the MIPI CSI-2 core
> and HSI core, and a clock for the D-PHY (oh and maybe a clock for an
> M-PHY if there is one). I have no clue what all these other clocks are.
> But anyway, a single gating bit, CCGR3[CG8], seems to enable them all.

I would imagine the CSI-2 core has a high-speed clock input from the
D-PHY for serial input, an APB clock for register access (ips_clk), and
a pixel clock input for the parallel output (pixel_clk), at least.
The D-PHY will have a PLL reference input (pll_refclk?) and probably its
own register clock (cfg_clk?).

I've looked at the MIPI DSI chapter, and it looks like ac_clk_125m is
used for DSI only.

> > Both cfg_clk and pll_refclk are sourced from video_27m, so "cfg" ->
> > video_27m seems fine.
> > But I don't get "dphy".
> 
> I presume it's the clock for the D-PHY.
>
> >   Which input clock would that correspond to?
> > "pll_refclk?"
> 
> the mux at CDCDR says it comes from PLL3_120M, or PLL2_PFD2.

I think that makes sense.

regards
Philipp