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Thu, 26 Jun 2025 21:56:42 -0700 (PDT) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250627-exynosdrm-decon-v3-0-5b456f88cfea@disroot.org> <20250627-exynosdrm-decon-v3-3-5b456f88cfea@disroot.org> In-Reply-To: <20250627-exynosdrm-decon-v3-3-5b456f88cfea@disroot.org> From: Inki Dae Date: Fri, 27 Jun 2025 13:56:06 +0900 X-Gm-Features: Ac12FXyCRtmqlVxLH-ZQ8PS-fwNE9eVFG2Sf48qY_m8XFevvCiJLCVczBK1_h0o Message-ID: Subject: Re: [PATCH v3 3/3] drm/exynos: exynos7_drm_decon: add vblank check in IRQ handling To: Kaustabh Chakraborty Cc: Seung-Woo Kim , Kyungmin Park , David Airlie , Simona Vetter , Krzysztof Kozlowski , Alim Akhtar , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Herring , Conor Dooley , Ajay Kumar , Akshu Agrawal , Krzysztof Kozlowski , Conor Dooley , dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 2025=EB=85=84 6=EC=9B=94 27=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 4:21, K= austabh Chakraborty =EB=8B=98=EC=9D=B4 =EC=9E=91=EC= =84=B1: > > If there's support for another console device (such as a TTY serial), > the kernel occasionally panics during boot. The panic message and a > relevant snippet of the call stack is as follows: > > Unable to handle kernel NULL pointer dereference at virtual address 000= 000000000000 > Call trace: > drm_crtc_handle_vblank+0x10/0x30 (P) > decon_irq_handler+0x88/0xb4 > [...] > It seems that if the display is already enabled by the bootloader during the boot process, a vblank interrupt may be triggered before the initialization of drm_dev is complete. This could be the root cause of the issue. Applied. Thanks, Inki Dae > Otherwise, the panics don't happen. This indicates that it's some sort > of race condition. > > Add a check to validate if the drm device can handle vblanks before > calling drm_crtc_handle_vblank() to avoid this. > > Cc: stable@vger.kernel.org > Fixes: 96976c3d9aff ("drm/exynos: Add DECON driver") > Signed-off-by: Kaustabh Chakraborty > --- > drivers/gpu/drm/exynos/exynos7_drm_decon.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/gpu/drm/exynos/exynos7_drm_decon.c b/drivers/gpu/drm= /exynos/exynos7_drm_decon.c > index 43bcbe2e2917df43d7c2d27a9771e892628dd682..c0c0f23169c993ac315fc8d7b= cbd09ea6ec9966a 100644 > --- a/drivers/gpu/drm/exynos/exynos7_drm_decon.c > +++ b/drivers/gpu/drm/exynos/exynos7_drm_decon.c > @@ -636,6 +636,10 @@ static irqreturn_t decon_irq_handler(int irq, void *= dev_id) > if (!ctx->drm_dev) > goto out; > > + /* check if crtc and vblank have been initialized properly */ > + if (!drm_dev_has_vblank(ctx->drm_dev)) > + goto out; > + > if (!ctx->i80_if) { > drm_crtc_handle_vblank(&ctx->crtc->base); > > > -- > 2.49.0 > >