Date: Wed, 10 Dec 2014 16:16:20 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Andrzej Hajda <a.hajda@samsung.com>
Cc: open list <linux-kernel@vger.kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mike Turquette <mturquette@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Alexandre Courbot <gnurou@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Inki Dae <inki.dae@samsung.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Liam Girdwood <lgirdwood@gmail.com>, Mark Brown <broonie@kernel.org>,
        Grant Likely <grant.likely@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        "moderated list:ARM/CLKDEV SUPPORT" 
	<linux-arm-kernel@lists.infradead.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
        "moderated list:ARM/S5P EXYNOS AR..." 
	<linux-samsung-soc@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND..." <devicetree@vger.kernel.org>,
        boris.brezillon@free-electrons.com
Subject: Re: [RFC 00/15] Resource tracking/allocation framework
Message-ID: <20141210161620.GM11285@n2100.arm.linux.org.uk>
References: <1418226513-14105-1-git-send-email-a.hajda@samsung.com>
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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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