From: Daniel Vetter <daniel@ffwll.ch>
To: Jyri Sarha <jsarha@ti.com>
Cc: "Valkeinen, Tomi" <tomi.valkeinen@ti.com>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>
Subject: Re: DRM driver and runtime suspend-resume handling?
Date: Tue, 14 Jan 2020 05:29:13 +0100 [thread overview]
Message-ID: <20200114042913.GF5340@dvetter-linux.ger.corp.intel.com> (raw)
In-Reply-To: <df769d2e-5fea-403f-2d04-b3239f89256f@ti.com>
On Mon, Jan 13, 2020 at 01:03:11PM +0200, Jyri Sarha wrote:
> Hi,
> While working with CRTC color related properties (gamma and CTM for
> instance) and making them persistent over suspend-resume cycle it
> occurred to me if I am just wasting resources by storing the property
> values in the driver and restoring them in dev_pm_ops runtime_resume()..
>
> Wouldn't it work if I would just:
>
> 1. Add a flag in the driver to indicate that the context may have been
> lost since the previous atomic commit and set in runtime_resume().
>
> 2. And write the color properties to HW if the context lost flag is set
> even if the drm_crtc_state color_mgmt_changed is false.
Still feels a bit too complicated, but might be needed for your hw. The
usual approach is:
- runtime pm within modeset enable/disable. Since atomic helpers always
enable the entire pipeline for a crtc enable/disable you can put the
runtime pm into each component (drm_crtc/encoder/bridge/...).
- just unconditionally restore everything in modeset enable, assuming
everything got lost.
- drm_atomic_helper_suspend/resume for system suspend/resume.
And you should be covevered. State save/restore in your driver code is
indeed an anti-pattern for modeset drivers, don't do that - ime at least
with fragile hw you'll get divergence between the two paths in minor
details, with some really hard to track down bugs as a result.
Ime tracking state changes and trying to be clever with when to restore
stuff (maybe outside of some atomic flip fastpath) in driver code only
attracts bugs :-)
> The color property values are there despite the color_mgmt_changed ==
> false, aren't they?
Yes.
Cheers, Daniel
>
> Best regards,
> Jyri
>
> --
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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prev parent reply other threads:[~2020-01-14 4:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 11:03 DRM driver and runtime suspend-resume handling? Jyri Sarha
2020-01-14 4:29 ` Daniel Vetter [this message]
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