linux-kernel - Re: [RFC 1/2] PM / Domains: Power on domain early during system resume

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Date:	Thu, 30 Oct 2014 12:01:35 +0100
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Kevin Hilman <khilman@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Inki Dae <inki.dae@...sung.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	David Airlie <airlied@...ux.ie>,
	Kukjin Kim <kgene.kim@...sung.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC 1/2] PM / Domains: Power on domain early during system resume

On 10/30/2014 08:36 AM, Krzysztof Kozlowski wrote:
> On śro, 2014-10-29 at 10:46 -0700, Kevin Hilman wrote:
>> Krzysztof Kozlowski <k.kozlowski@...sung.com> writes:
>>
>>> When resuming the system the power domain has to be powered on early so
>>> any runtime PM aware devices could resume.
>>>
>>> This fixes following scenario reproduced on Exynos DRM:
>>> 1. Power domain is off before suspending the system.
>>> 2. System is suspended to RAM.
>>> 3. Resuming starts. The Exynos DRM driver resume callback is called.
>>> 4. The Exynos DRM driver calls drm_helper_resume_force_mode which turns
>>>    the screen on by calling exynos_dsi_dpms with DRM_MODE_DPMS_ON.
>> Dumb Q: if the device (and power domain) were off before (and during)
>> suspend, why are they being resumed?
>>
>> Shouldn't the resume path restore things to the same state they were
>> before suspend?
> One could expect that... but the Exynos DRM driver behaves differently
> (and some other drivers also). In resume method it calls
> drm_helper_resume_force_mode() which forces restoring mode setting
> configuration. Apparently setting a mode needs DPMS on:
> static void exynos_drm_crtc_commit(struct drm_crtc *crtc)
> {
> 	...
> 	exynos_drm_crtc_dpms(crtc, DRM_MODE_DPMS_ON);
> 	...
>
> The previous DPMS status (status during suspend) is completely ignored
> here.

Suspend callback switches off all connectors (thus all other devs in
their pipeline) by calling dpms_off,
in restore callback all devs are restored to their previous state by
calling appropriate dpms.
So I guess drm_helper_resume_force_mode() call at the end of resume is
incorrect.
On the other side it is present in many other drivers, so I am also
little bit confused.

Regards
Andrzej


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