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[34.150.146.164]) by smtp.gmail.com with ESMTPSA id i2-20020ac80042000000b003ef28a76a11sm59598qtg.68.2023.05.05.11.46.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 May 2023 11:46:04 -0700 (PDT) Date: Fri, 5 May 2023 18:46:04 +0000 From: Sean Paul To: Brian Norris Cc: Heiko =?iso-8859-1?Q?St=FCbner?= , Daniel Vetter , Sean Paul , Michel =?iso-8859-1?Q?D=E4nzer?= , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Sandy Huang , linux-rockchip@lists.infradead.org, stable@vger.kernel.org Subject: Re: [PATCH v3 1/2] drm/atomic: Allow vblank-enabled + self-refresh "disable" Message-ID: References: <20230109171809.v3.1.I3904f697863649eb1be540ecca147a66e42bfad7@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230109171809.v3.1.I3904f697863649eb1be540ecca147a66e42bfad7@changeid> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Jan 09, 2023 at 05:18:16PM -0800, Brian Norris wrote: > The self-refresh helper framework overloads "disable" to sometimes mean > "go into self-refresh mode," and this mode activates automatically > (e.g., after some period of unchanging display output). In such cases, > the display pipe is still considered "on", and user-space is not aware > that we went into self-refresh mode. Thus, users may expect that > vblank-related features (such as DRM_IOCTL_WAIT_VBLANK) still work > properly. > > However, we trigger the WARN_ONCE() here if a CRTC driver tries to leave > vblank enabled. > > Add a different expectation: that CRTCs *should* leave vblank enabled > when going into self-refresh. > > This patch is preparation for another patch -- "drm/rockchip: vop: Leave > vblank enabled in self-refresh" -- which resolves conflicts between the > above self-refresh behavior and the API tests in IGT's kms_vblank test > module. > > == Some alternatives discussed: == > > It's likely that on many display controllers, vblank interrupts will > turn off when the CRTC is disabled, and so in some cases, self-refresh > may not support vblank. To support such cases, we might consider > additions to the generic helpers such that we fire vblank events based > on a timer. > > However, there is currently only one driver using the common > self-refresh helpers (i.e., rockchip), and at least as of commit > bed030a49f3e ("drm/rockchip: Don't fully disable vop on self refresh"), > the CRTC hardware is powered enough to continue to generate vblank > interrupts. > > So we chose the simpler option of leaving vblank interrupts enabled. We > can reevaluate this decision and perhaps augment the helpers if/when we > gain a second driver that has different requirements. > > v3: > * include discussion summary > > v2: > * add 'ret != 0' warning case for self-refresh > * describe failing test case and relation to drm/rockchip patch better > > Cc: # dependency for "drm/rockchip: vop: Leave > # vblank enabled in self-refresh" > Signed-off-by: Brian Norris Pushed both patches to drm-misc-next, thanks Brian > --- > drivers/gpu/drm/drm_atomic_helper.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c > index d579fd8f7cb8..a22485e3e924 100644 > --- a/drivers/gpu/drm/drm_atomic_helper.c > +++ b/drivers/gpu/drm/drm_atomic_helper.c > @@ -1209,7 +1209,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state) > continue; > > ret = drm_crtc_vblank_get(crtc); > - WARN_ONCE(ret != -EINVAL, "driver forgot to call drm_crtc_vblank_off()\n"); > + /* > + * Self-refresh is not a true "disable"; ensure vblank remains > + * enabled. > + */ > + if (new_crtc_state->self_refresh_active) > + WARN_ONCE(ret != 0, > + "driver disabled vblank in self-refresh\n"); > + else > + WARN_ONCE(ret != -EINVAL, > + "driver forgot to call drm_crtc_vblank_off()\n"); > if (ret == 0) > drm_crtc_vblank_put(crtc); > } > -- > 2.39.0.314.g84b9a713c41-goog > -- Sean Paul, Software Engineer, Google / Chromium OS