linux-kernel - Re: [RFC 00/15] Resource tracking/allocation framework

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Message-ID: <20141210161620.GM11285@n2100.arm.linux.org.uk>
Date:	Wed, 10 Dec 2014 16:16:20 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	open list <linux-kernel@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mike Turquette <mturquette@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Inki Dae <inki.dae@...sung.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"moderated list:ARM/CLKDEV SUPPORT" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
	"open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
	"moderated list:ARM/S5P EXYNOS AR..." 
	<linux-samsung-soc@...r.kernel.org>,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	boris.brezillon@...e-electrons.com
Subject: Re: [RFC 00/15] Resource tracking/allocation framework

On Wed, Dec 10, 2014 at 04:48:18PM +0100, Andrzej Hajda wrote:
> 3. There are drivers which can work without specific resource, but if
>   the resource becomes available/unavailable it can do some additional stuff.
>   An example of such driver is DRM driver (more precisely drm_connector) -
>   it can start without attached drm_panel, but if the panel becomes available it
>   can react by generating HPD event and start using it.

Bad example, and actually incorrect.  DRM connectors are referenced in
userspace by an IDR number, which can be re-used in the case of a
connector appearing, disappearing, and then a different connector
re-appearing.

DRM really is *not* safe to hotplug like this: DRM is more a card-level
thing, which is why we have the component helpers - which allow us to
merge several devices into one logical card-like device in a generic
manner.

DRM needs a stable picture of the CRTCs, encoders and connectors, which
should _never_ change during the lifetime of the DRM device.  Devices
attached to connectors can be hotplugged, but that's about the limit of
hot-plugging in DRM.

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