linux-kernel - Re: [PATCHv4 5/8] drm: tegra: Remove redundant host1x

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Message-ID: <50E133F8.40106@nvidia.com>
Date:	Mon, 31 Dec 2012 08:43:04 +0200
From:	Terje Bergström <tbergstrom@...dia.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Stephen Warren <swarren@...dotorg.org>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"dev@...xeye.de" <dev@...xeye.de>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arto Merilainen <amerilainen@...dia.com>
Subject: Re: [PATCHv4 5/8] drm: tegra: Remove redundant host1x

On 28.12.2012 23:21, Thierry Reding wrote:
> Instead of going over this back and forth, I've decided to rewrite this
> patch from scratch the way I think it should be done. Maybe that'll make
> things clearer. I haven't tested it on real hardware yet because I don't
> have access over the holidays, but I'll post the patch once I've
> verified that it actually works. The code is based on patches 1-4 of
> this series and is meant to replace patch 5.

I'm still not happy that host1x needs to know about drm. That's just a
wrong dependency, and wrong dependencies always end up biting back. We
need to figure out solution that satisfies both mine and your
requirements and reduce complexity.

DC/HDMI/GR2D probes are using the global data only for managing the
lists "drm_clients" and "clients". "clients" list is only required after
tegra_drm_load(). "drm_clients" is required to establish driver load order.

With dummy device, we can determine the registration (and probe) order.
tegra-drm can register the drivers for DC/HDMI/GR2D devices first, and
as last the device and driver for tegra-drm.

tegra-drm probe will allocate the global data, enumerate all drivers and
add them to the clients list. If one driver is not initialized, it'll
return with -EPROBE_DEFER and will be called again later. When all this
is successful, it'll call drm_platform_init().

The advantages:
 * No management of drm_clients list
 * No mucking with drvdata
 * host1x doesn't need to know about drm
 * The global data is allocated and deallocated by tegra-drm probe and
remove, and accessed only via drm_device->dev_private
 * Much less code

Something like the attached patch - not tested, as I don't have access
to hw now, but it shows the idea. It's based on patches 1-5 in the
series, and could replace patch 5.

Terje

View attachment "0001-drm-tegra-Postpone-usage-of-global-data.patch" of type "text/x-patch" (11603 bytes)