linux-kernel - Re: [PATCH v2 1/4] drm: arm: Add DT bindings documentation for HDLCD driver.

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Message-ID: <20151113101156.GE963@e106497-lin.cambridge.arm.com>
Date:	Fri, 13 Nov 2015 10:11:56 +0000
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Rob Herring <robh@...nel.org>
Cc:	David Airlie <airlied@...ux.ie>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Jon Medhurst <tixy@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Pawel Moll <pawel.moll@....com>, Arnd Bergmann <arnd@...db.de>,
	Olof Johansson <olof@...om.net>,
	Punit Agrawal <punit.agrawal@....com>,
	DRI devel <dri-devel@...ts.freedesktop.org>,
	devicetree <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] drm: arm: Add DT bindings documentation for HDLCD
 driver.

On Thu, Nov 12, 2015 at 09:30:31PM -0600, Rob Herring wrote:
> On Thu, Nov 12, 2015 at 4:42 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > On Wed, Nov 11, 2015 at 12:48:50PM -0600, Rob Herring wrote:
> >> On Wed, Nov 11, 2015 at 04:06:47PM +0000, Liviu Dudau wrote:
> >> > Cc: Rob Herring <robh+dt@...nel.org>
> >> > Cc: Pawel Moll <pawel.moll@....com>
> >> > Cc: Mark Rutland <mark.rutland@....com>
> >> > Cc: Ian Campbell <ijc+devicetree@...lion.org.uk>
> >> > Cc: Kumar Gala <galak@...eaurora.org>
> >> >
> >> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> >>
> >> Looks pretty good, but a few comments.
> >>
> >> > ---
> >> >  .../devicetree/bindings/drm/arm/arm,hdlcd.txt      | 74 ++++++++++++++++++++++
> >> >  1 file changed, 74 insertions(+)
> >> >  create mode 100644 Documentation/devicetree/bindings/drm/arm/arm,hdlcd.txt
> >> >
> >> > diff --git a/Documentation/devicetree/bindings/drm/arm/arm,hdlcd.txt b/Documentation/devicetree/bindings/drm/arm/arm,hdlcd.txt
> >> > new file mode 100644
> >> > index 0000000..b57f1b9
> >> > --- /dev/null
> >> > +++ b/Documentation/devicetree/bindings/drm/arm/arm,hdlcd.txt
> >> > @@ -0,0 +1,74 @@
> >> > +ARM HDLCD
> >> > +
> >> > +This is a display controller found on several development platforms produced
> >> > +by ARM Ltd and in more modern of its' Fast Models. The HDLCD is an RGB
> >> > +streamer that reads the data from a framebuffer and sends it to a single
> >> > +digital encoder (DVI or HDMI).
> >> > +
> >> > +Required properties:
> >> > +  - compatible: "arm,hdlcd"
> >>
> >> Kind of generic. Something more specific please.
> >
> > "There can be only one!" (hdlcd) :) This is going to be a "one version only" HW part.
> > ARM has now switched to a new display hardware that has more features and a new name,
> > and work on mainlining support for that will start once I get the HDLCD driver accepted.
> 
> So there is never going to be a single difference across platforms.

Correct, there is only one implementation available. AFAIK there are no plans to make changes to it.

> Variations in max clock for different FPGAs?

The clock is external to the part and there is a check in the driver if we can set the frequency
to match the requested dotclock by the video_mode. It does not affect the hardware or how it presents
itself to the driver.

> 
> 
> >> > +  - reg: Physical base address and length of the controller's registers.
> >> > +    If a second pair of address and length values is present this specifies
> >> > +    the presence of a DMA coherent memory area that the HDLCD can use as
> >> > +    framebuffer instead of normal CMA memory.
> >>
> >> This is on-chip RAM or nornal system RAM? We already have bindings for
> >> both.
> >
> > Juno has a set of TLX (ThinLinks) connectors on the board where an FPGA can be attached. On r1
> > the code running on FPGA can even participate as an AXI master with full coherency. The FPGA
> > has local memory that we want to share with the HDLCD to be used as a framebuffer.
> 
> So describe the memory region and then use a memory-region phandle to
> the memory here.

OK, I will.

> 
> >> > +  - interrupts: One interrupt used by the display controller to notify the
> >> > +    interrupt controller when any of the interrupt sources programmed in
> >> > +    the interrupt mask register have activated.
> >> > +  - clocks: A list of phandle + clock-specifier pairs, one for each
> >> > +    entry in 'clock-names'.
> >> > +  - clock-names: A list of clock names. For HDLD it should contain:
> 
> typo: HDLD

oops, thanks, will fix.

> 
> >> > +      - "pxlclk" for the clock feeding the output PLL of the controller.
> >> > +  - port: The HDLCD connection to an encoder chip. The connection is modelled
> 
> s/modelled/modeled/

ditto.

Thanks for reviewing it,
Liviu

> 
> Rob
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
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