linux-kernel - Re: [PATCH 2/4] drm: Add support for ARM's HDLCD controller.

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Date:	Sun, 16 Aug 2015 09:56:33 +0100
From:	Emil Velikov <emil.l.velikov@...il.com>
To:	Liviu Dudau <Liviu.Dudau@....com>
Cc:	David Airlie <airlied@...ux.ie>,
	ML dri-devel <dri-devel@...ts.freedesktop.org>,
	linux-arm-kernel@...ts.infradead.org,
	Mark Rutland <mark.rutland@....com>,
	Jon Medhurst <tixy@...aro.org>, Arnd Bergmann <arnd@...db.de>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Will Deacon <will.deacon@....com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 2/4] drm: Add support for ARM's HDLCD controller.

Hi Liviu,

On 5 August 2015 at 15:28, Liviu Dudau <Liviu.Dudau@....com> wrote:
> The HDLCD controller is a display controller that supports resolutions
> up to 4096x4096 pixels. It is present on various development boards
> produced by ARM Ltd and emulated by the latest Fast Models from the
> company.
>
I believe there is a unofficial requirement(?) for new drm drivers to
use atomic modesetting. Not 100% sure on this one though. The
following drivers: tegra, msm, rcar-du, i915, and Daniel's blog [1]
[2] cat provide some information on the topic.

The driver seems to has has a bit of dead code guarded by
HDLCD_*_UNDERRUN. Perhaps these macros should become build or runtime
switch(es) ?

Most DRM drivers do not threat dma, bus_error, vsync and/or underrun
interrupts as debug functionality. They are of limited use in this
driver, presently, yet the CONFIG_DEBUG_FS guard seems a bit strange
imho.

Cheers,
Emil

[1] http://blog.ffwll.ch/2014/11/atomic-modeset-support-for-kms-drivers.html
[2] http://blog.ffwll.ch/2015/01/update-for-atomic-display-updates.html
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