From mboxrd@z Thu Jan 1 00:00:00 1970 From: khilman@kernel.org (Kevin Hilman) Date: Mon, 03 Nov 2014 08:13:17 -0800 Subject: [RFC 1/2] PM / Domains: Power on domain early during system resume In-Reply-To: <54521A8F.5070808@samsung.com> (Andrzej Hajda's message of "Thu, 30 Oct 2014 12:01:35 +0100") References: <1414072090-11293-1-git-send-email-k.kozlowski@samsung.com> <1414072090-11293-2-git-send-email-k.kozlowski@samsung.com> <7hk33iahvu.fsf@deeprootsystems.com> <1414654594.5114.8.camel@AMDC1943> <54521A8F.5070808@samsung.com> Message-ID: <7hbnoojm8y.fsf@deeprootsystems.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Andrzej Hajda writes: > On 10/30/2014 08:36 AM, Krzysztof Kozlowski wrote: >> On ?ro, 2014-10-29 at 10:46 -0700, Kevin Hilman wrote: >>> Krzysztof Kozlowski 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. Though I'm not terribly familiar with DRM, it seems incorrect because I expect resume to restore the state of things when suspend happened, not forcibly resume everything. > On the other side it is present in many other drivers, so I am also > little bit confused. Many other DRM drivers? or other drivers too? Kevin