linux-kernel - [PATCH v2 2/2] drm/exynos: exynos7_drm_decon: add vblank check in IRQ handling

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Message-Id: <20250612-exynosdrm-decon-v2-2-d6c1d21c8057@disroot.org>
Date: Thu, 12 Jun 2025 20:29:20 +0530
From: Kaustabh Chakraborty <kauschluss@...root.org>
To: Inki Dae <inki.dae@...sung.com>, Seung-Woo Kim <sw0312.kim@...sung.com>, 
 Kyungmin Park <kyungmin.park@...sung.com>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, Krzysztof Kozlowski <krzk@...nel.org>, 
 Alim Akhtar <alim.akhtar@...sung.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 Rob Herring <robh@...nel.org>, Conor Dooley <conor@...nel.org>, 
 Ajay Kumar <ajaykumar.rs@...sung.com>, Akshu Agrawal <akshua@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
 linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 devicetree@...r.kernel.org, Kaustabh Chakraborty <kauschluss@...root.org>, 
 stable@...r.kernel.org
Subject: [PATCH v2 2/2] drm/exynos: exynos7_drm_decon: add vblank check in
 IRQ handling

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 000000000000000
  Call trace:
    drm_crtc_handle_vblank+0x10/0x30 (P)
    decon_irq_handler+0x88/0xb4
    [...]

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@...r.kernel.org
Fixes: 96976c3d9aff ("drm/exynos: Add DECON driver")
Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
---
 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..c0c0f23169c993ac315fc8d7bcbd09ea6ec9966a 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