From: Daniel Vetter <daniel@ffwll.ch>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Daniel Vetter <daniel@ffwll.ch>,
Maxime Ripard <maxime.ripard@free-electrons.com>,
Mike Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@codeaurora.org>,
David Airlie <airlied@linux.ie>,
Thierry Reding <thierry.reding@gmail.com>,
Philipp Zabel <p.zabel@pengutronix.de>,
devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org,
dri-devel@lists.freedesktop.org, linux-sunxi@googlegroups.com,
Chen-Yu Tsai <wens@csie.org>, Hans de Goede <hdegoede@redhat.com>,
Alexander Kaplan <alex@nextthing.co>,
Boris Brezillon <boris.brezillon@free-electrons.com>,
Wynter Woods <wynter@nextthing.co>,
Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
Rob Clark <robdclark@gmail.com>
Subject: Re: [PATCH v2 13/26] drm/fb_cma_helper: Remove implicit call to disable_unused_functions
Date: Mon, 25 Jan 2016 08:29:38 +0100 [thread overview]
Message-ID: <20160125072938.GI11240@phenom.ffwll.local> (raw)
In-Reply-To: <1484612.l42nGNbAu5@avalon>
On Mon, Jan 25, 2016 at 12:19:27AM +0200, Laurent Pinchart wrote:
> Hi Daniel,
>
> On Friday 15 January 2016 11:17:30 Daniel Vetter wrote:
> > On Fri, Jan 15, 2016 at 01:13:05AM +0200, Laurent Pinchart wrote:
> > > On Thursday 14 January 2016 16:24:56 Maxime Ripard wrote:
> > >> The drm_fbdev_cma_init function always calls the
> > >> drm_helper_disable_unused_functions. Since it's part of the usual probe
> > >> process, all the drivers using that helper will end up having their
> > >> encoder and CRTC disable functions called at probe if their device has
> > >> not been reported as enabled.
> > >>
> > >> This could be fixed by reading out from the registers the current state
> > >> of the device if it is enabled, but even that will not handle the case
> > >> where the device is actually disabled.
> > >>
> > >> Moreover, the drivers using the atomic modesetting expect that their
> > >> enable and disable callback to be called when the device is already
> > >> enabled or disabled (respectively).
> > >>
> > >> We can however fix this issue by moving the call to
> > >> drm_helper_disable_unused_functions out of drm_fbdev_cma_init and make
> > >> the drivers needing it (all the drivers calling drm_fbdev_cma_init and
> > >> not using the atomic modesetting) explicitly call it.
> > >
> > > I'd rather add it to all drivers that call drm_fbdev_cma_init(). All the
> > > atomic ones must have special code to cope with it that could be rendered
> > > useless by the removal of the drm_helper_disable_unused_functions() call.
> > > That code should be removed too, and it would be easier to check drivers
> > > one by one and fixing them individually (outside of this patch series,
> > > unless you insist ;-)) when removing the explicit
> > > drm_helper_disable_unused_functions() call.
> >
> > I had the same thought, but figured there's really no good reason ever to
> > do this. I suspect most of that disable_unused_function stuff we have all
> > over is supreme cargo-cult anyway ;-)
>
> I'm not sure you got my point. Yes, the drm_helper_disable_unused_functions()
> call should be removed from atomic drivers, but that will leave support code
> added for the sole reason of avoiding the crash in the drivers. That code will
> likely not be noticed and will stay there rotting. If we added
> drm_helper_disable_unused_functions() calls to all atomic drivers then driver
> authors will hopefully check carefully if there's any support code that can be
> removed when removing the function call. It would act as a kind of FIXME
> reminder.
drm_helper_disable_unused_functions() already prefers the ->disable
callbacks over dpms, like atomic helpers. I don't think there's any dead
code due to this change. The problem was that driver/hw blew up since it
was disabled when the hw was off already.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2016-01-25 7:29 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-14 15:24 [PATCH v2 00/26] drm: Add Allwinner A10 display engine support Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 01/26] reset: Move DT cell size check to the core Maxime Ripard
2016-01-15 15:50 ` Philipp Zabel
2016-01-14 15:24 ` [PATCH v2 02/26] reset: Make reset_control_ops const Maxime Ripard
2016-01-15 15:50 ` Philipp Zabel
2016-01-14 15:24 ` [PATCH v2 03/26] clk: Add regmap support Maxime Ripard
2016-01-28 7:56 ` Stephen Boyd
2016-01-14 15:24 ` [PATCH v2 04/26] clk: composite: Add unregister function Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 05/26] clk: sunxi: Add display and TCON0 clocks driver Maxime Ripard
2016-01-15 3:01 ` Rob Herring
2016-01-16 14:08 ` [linux-sunxi] " Priit Laes
2016-01-16 15:29 ` Chen-Yu Tsai
2016-02-03 20:18 ` Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 06/26] clk: sunxi: Add PLL3 clock Maxime Ripard
2016-01-15 3:02 ` Rob Herring
2016-01-16 16:05 ` Chen-Yu Tsai
2016-02-03 20:27 ` Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 07/26] clk: sunxi: Add TCON channel1 clock Maxime Ripard
2016-01-15 3:03 ` Rob Herring
2016-01-16 16:36 ` Chen-Yu Tsai
2016-02-03 20:29 ` Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 08/26] clk: sun5i: add DRAM gates Maxime Ripard
2016-01-15 3:04 ` Rob Herring
2016-01-14 15:24 ` [PATCH v2 09/26] ARM: sun5i: dt: Add pll3 and pll7 clocks Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 10/26] ARM: sun5i: a13: Add display and TCON clocks Maxime Ripard
2016-01-16 17:06 ` Chen-Yu Tsai
2016-02-03 20:31 ` Maxime Ripard
2016-02-05 9:49 ` Chen-Yu Tsai
2016-01-14 15:24 ` [PATCH v2 11/26] ARM: sun5i: Add DRAM gates Maxime Ripard
2016-01-16 17:10 ` Chen-Yu Tsai
2016-02-03 20:36 ` Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 12/26] ARM: sun5i: Add TV encoder gate to the DTSI Maxime Ripard
2016-01-16 17:12 ` Chen-Yu Tsai
2016-01-14 15:24 ` [PATCH v2 13/26] drm/fb_cma_helper: Remove implicit call to disable_unused_functions Maxime Ripard
2016-01-14 23:13 ` Laurent Pinchart
2016-01-15 10:17 ` Daniel Vetter
2016-01-24 22:19 ` Laurent Pinchart
2016-01-25 7:29 ` Daniel Vetter [this message]
2016-01-25 19:02 ` Laurent Pinchart
2016-01-14 15:24 ` [PATCH v2 14/26] drm/modes: Rewrite the command line parser Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 15/26] drm/modes: Support modes names on the command line Maxime Ripard
2016-01-14 15:24 ` [PATCH v2 16/26] drm: Add Allwinner A10 Display Engine support Maxime Ripard
2016-01-16 15:11 ` [linux-sunxi] " Priit Laes
2016-01-17 12:58 ` Priit Laes
2016-01-19 15:38 ` Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 17/26] drm: sun4i: Add DT bindings documentation Maxime Ripard
2016-01-15 3:15 ` Rob Herring
2016-02-03 19:59 ` Maxime Ripard
2016-02-03 20:19 ` Rob Herring
2016-02-03 20:47 ` Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 18/26] drm: sun4i: Add RGB output Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 19/26] drm: sun4i: Add composite output Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 20/26] drm: sun4i: tv: Add PAL output standard Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 21/26] drm: sun4i: tv: Add NTSC " Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 22/26] ARM: sun5i: r8: Add display blocks to the DTSI Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 23/26] ARM: sun5i: chip: Enable the TV Encoder Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 24/26] devicetree: Add olimex vendor prefix Maxime Ripard
2016-01-15 3:15 ` Rob Herring
2016-01-15 6:41 ` Stefan Wahren
2016-01-15 8:05 ` Maxime Ripard
2016-01-14 15:25 ` [PATCH v2 25/26] drm/panel: simple: Add timings for the Olimex LCD-OLinuXino-4.3TS Maxime Ripard
2016-01-15 3:17 ` Rob Herring
2016-01-14 15:25 ` [PATCH v2 26/26] DO NOT MERGE: ARM: sun5i: chip: Enable the LCD panel Maxime Ripard
2016-02-20 13:45 ` [linux-sunxi] [PATCH v2 00/26] drm: Add Allwinner A10 display engine support Priit Laes
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