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

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Message-ID: <20151112104210.GZ963@e106497-lin.cambridge.arm.com>
Date:	Thu, 12 Nov 2015 10:42:10 +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 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. 

> 
> > +  - 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.

> 
> > +  - 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:
> > +      - "pxlclk" for the clock feeding the output PLL of the controller.
> > +  - port: The HDLCD connection to an encoder chip. The connection is modelled
> > +    using the OF graph bindings specified in Documentation/devicetree/bindings/graph.txt.
> 

Thanks for reviewing this,
Liviu

-- 
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