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From: Thierry Reding <thierry.reding@gmail.com>
To: Rob Clark <robdclark@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>,
	Stephen Boyd <sboyd@codeaurora.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
	Mike Turquette <mturquette@linaro.org>
Subject: Re: [PATCH 01/36] clk: Introduce clk_try_parent()
Date: Wed, 21 Jan 2015 16:12:13 +0100	[thread overview]
Message-ID: <20150121151210.GC22884@ulmo.nvidia.com> (raw)
In-Reply-To: <CAF6AEGsPGCAHxqqRR7wWGxbiuS1HwTxF8fMb=VaL8T_qj85=TQ@mail.gmail.com>


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On Tue, Jan 20, 2015 at 01:16:16PM -0500, Rob Clark wrote:
> On Tue, Jan 20, 2015 at 1:02 PM, Mike Turquette <mturquette@linaro.org> wrote:
> > Quoting Thierry Reding (2015-01-20 02:48:20)
> >> From: Thierry Reding <treding@nvidia.com>
> >>
> >> This new function is similar to clk_set_parent(), except that it doesn't
> >> actually change the parent. It merely checks that the given parent clock
> >> can be a parent for the given clock.
> >>
> >> A situation where this is useful is to check that a particular setup is
> >> valid before switching to it. One specific use-case for this is atomic
> >> modesetting in the DRM framework where setting a mode is divided into a
> >> check phase where a given configuration is validated before applying
> >> changes to the hardware.
> >
> > Can you describe why this was needed for your atomic modesetting work?
> > What problem did you hit in the driver that required this new check?
> 
> In particular, for an async atomic update, we need to do everything
> that may potentially fail up front before returning to userspace.
> Additionally there is a 'testonly' flag so that userspace can ask if a
> particular display configuration is possible.

One specific use-case where this is needed is if we want to set a mode
but halfway through the modeset we find out that we can't actually set
it, then we need to somehow rollback the changes, or be stuck with a
mode that doesn't work.

Splitting this into two separate stages allows all the checks to be
performed before making any changes to the hardware. The current mode
will remain active until the changes are committed. Therefore rollback
of a partial modeset is not required.

Thierry

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  reply	other threads:[~2015-01-21 15:12 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-20 10:48 [PATCH 00/36] drm/tegra: Atomic mode-setting conversion Thierry Reding
2015-01-20 10:48 ` [PATCH 01/36] clk: Introduce clk_try_parent() Thierry Reding
2015-01-20 18:02   ` Mike Turquette
2015-01-20 18:16     ` Rob Clark
2015-01-21 15:12       ` Thierry Reding [this message]
     [not found]   ` <1421750935-4023-2-git-send-email-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-01-20 19:21     ` Stephen Boyd
2015-01-21 15:05       ` Thierry Reding
2015-01-21 16:13   ` [PATCH v2] clk: Introduce clk_has_parent() Thierry Reding
     [not found]     ` <1421856780-32103-1-git-send-email-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-01-22  0:16       ` Stephen Boyd
     [not found]         ` <54C04145.1010906-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2015-01-22  7:37           ` Thierry Reding
2015-01-22 20:25             ` Stephen Boyd
2015-01-23  9:34               ` Thierry Reding
2015-01-25  1:02                 ` Mike Turquette
2015-01-20 10:48 ` [PATCH 02/36] drm/plane: Make ->atomic_update() mandatory Thierry Reding
2015-01-20 11:10   ` Daniel Vetter
     [not found]   ` <1421750935-4023-3-git-send-email-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-01-20 13:51     ` Rob Clark
2015-01-23  9:18       ` Thierry Reding
2015-01-23  9:26     ` [PATCH v2] " Thierry Reding
2015-01-20 10:48 ` [PATCH 03/36] drm/plane: Add optional ->atomic_disable() callback Thierry Reding
2015-01-20 11:13   ` Daniel Vetter
2015-01-22 18:57   ` Gustavo Padovan
2015-01-23  9:28   ` [PATCH v4] " Thierry Reding
2015-01-20 10:48 ` [PATCH 04/36] drm/atomic: Add ->atomic_check() to encoder helpers Thierry Reding
2015-01-20 11:07   ` Daniel Vetter
2015-01-20 10:48 ` [PATCH 05/36] drm/atomic: Add drm_atomic_plane_get_crtc_state() Thierry Reding
2015-01-20 11:10   ` Daniel Vetter
     [not found]     ` <20150120111011.GX10113-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2015-01-23  9:32       ` Thierry Reding
2015-01-20 10:48 ` [PATCH 06/36] drm/tegra: Use tegra_commit_dc() in output drivers Thierry Reding
2015-01-20 10:48 ` [PATCH 07/36] drm/tegra: Stop CRTC at CRTC disable time Thierry Reding
2015-01-20 10:48 ` [PATCH 08/36] drm/tegra: dc: Wait for idle when disabled Thierry Reding
2015-01-20 10:48 ` [PATCH 09/36] drm/tegra: Move tegra_drm_mode_funcs to the core Thierry Reding
2015-01-20 10:48 ` [PATCH 10/36] drm/tegra: dc: No longer disable planes at CRTC disable Thierry Reding
2015-01-20 10:48 ` [PATCH 11/36] drm/tegra: Convert output midlayer to helpers Thierry Reding
2015-01-20 10:48 ` [PATCH 12/36] drm/tegra: output: Make ->setup_clock() optional Thierry Reding
2015-01-20 10:48 ` [PATCH 13/36] drm/tegra: Add tegra_dc_setup_clock() helper Thierry Reding
2015-01-20 10:48 ` [PATCH 14/36] drm/tegra: rgb: Demidlayer Thierry Reding
2015-01-20 10:48 ` [PATCH 15/36] drm/tegra: hdmi: Demidlayer Thierry Reding
2015-01-20 10:48 ` [PATCH 16/36] drm/tegra: dsi: Demidlayer Thierry Reding
2015-01-20 10:48 ` [PATCH 17/36] drm/tegra: sor: Demidlayer Thierry Reding
2015-01-20 10:48 ` [PATCH 18/36] drm/tegra: debugfs cleanup cannot fail Thierry Reding
2015-01-20 10:48 ` [PATCH 19/36] drm/tegra: Remove remnants of the output midlayer Thierry Reding
2015-01-20 10:48 ` [PATCH 20/36] drm/tegra: Output cleanup functions cannot fail Thierry Reding
2015-01-20 10:48 ` [PATCH 21/36] drm/tegra: dc: Do not needlessly deassert reset Thierry Reding
2015-01-20 10:48 ` [PATCH 22/36] drm/tegra: Atomic conversion, phase 1 Thierry Reding
2015-01-20 10:48 ` [PATCH 23/36] drm/tegra: Atomic conversion, phase 2 Thierry Reding
2015-01-20 10:48 ` [PATCH 24/36] drm/tegra: Atomic conversion, phase 3, step 1 Thierry Reding
2015-01-20 10:48 ` [PATCH 25/36] drm/tegra: dc: Store clock setup in atomic state Thierry Reding
2015-01-20 10:48 ` [PATCH 26/36] drm/tegra: rgb: Implement ->atomic_check() Thierry Reding
2015-01-20 10:48 ` [PATCH 27/36] drm/tegra: dsi: " Thierry Reding
2015-01-20 10:48 ` [PATCH 28/36] drm/tegra: hdmi: " Thierry Reding
2015-01-20 10:48 ` [PATCH 29/36] drm/tegra: sor: " Thierry Reding
2015-01-20 10:48 ` [PATCH 30/36] drm/tegra: dc: Use atomic clock state in modeset Thierry Reding
2015-01-20 10:48 ` [PATCH 31/36] drm/tegra: Atomic conversion, phase 3, step 2 Thierry Reding
2015-01-20 10:48 ` [PATCH 32/36] drm/tegra: Atomic conversion, phase 3, step 3 Thierry Reding
2015-01-20 10:48 ` [PATCH 33/36] drm/tegra: Remove unused ->mode_fixup() callbacks Thierry Reding
2015-01-20 10:48 ` [PATCH 34/36] drm/tegra: Track active planes in CRTC state Thierry Reding
2015-01-20 11:18   ` Daniel Vetter
2015-01-20 11:43     ` Thierry Reding
     [not found]   ` <1421750935-4023-35-git-send-email-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-01-23  9:31     ` [PATCH v2] " Thierry Reding
2015-01-20 10:48 ` [PATCH 35/36] drm/tegra: Track tiling and format in plane state Thierry Reding
2015-01-20 10:48 ` [PATCH 36/36] drm/tegra: dc: Unify enabling the display controller Thierry Reding

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