linux-kernel - [PATCH drm-misc-next v2 6/9] drm/arm/malidp: plane: protect device resources after removal

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Message-Id: <20221001163946.534067-7-dakr@redhat.com>
Date:   Sat,  1 Oct 2022 18:39:43 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        mripard@...nel.org, liviu.dudau@....com, brian.starkey@....com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Danilo Krummrich <dakr@...hat.com>
Subject: [PATCH drm-misc-next v2 6/9] drm/arm/malidp: plane: protect device resources after removal

(Hardware) resources which are bound to the driver and device lifecycle
must not be accessed after the device and driver are unbound.

However, the DRM device isn't freed as long as the last user didn't
close it, hence userspace can still call into the driver.

Therefore protect the critical sections which are accessing those
resources with drm_dev_enter() and drm_dev_exit().

Signed-off-by: Danilo Krummrich <dakr@...hat.com>
---
 drivers/gpu/drm/arm/malidp_planes.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/arm/malidp_planes.c b/drivers/gpu/drm/arm/malidp_planes.c
index 34547edf1ee3..d2ea60549454 100644
--- a/drivers/gpu/drm/arm/malidp_planes.c
+++ b/drivers/gpu/drm/arm/malidp_planes.c
@@ -790,9 +790,12 @@ static void malidp_de_plane_update(struct drm_plane *plane,
 	u16 pixel_alpha = new_state->pixel_blend_mode;
 	u8 plane_alpha = new_state->alpha >> 8;
 	u32 src_w, src_h, dest_w, dest_h, val;
-	int i;
+	int i, idx;
 	struct drm_framebuffer *fb = plane->state->fb;
 
+	if (!drm_dev_enter(plane->dev, &idx))
+		return;
+
 	mp = to_malidp_plane(plane);
 
 	/*
@@ -897,16 +900,24 @@ static void malidp_de_plane_update(struct drm_plane *plane,
 
 	malidp_hw_write(mp->hwdev, val,
 			mp->layer->base + MALIDP_LAYER_CONTROL);
+
+	drm_dev_exit(idx);
 }
 
 static void malidp_de_plane_disable(struct drm_plane *plane,
 				    struct drm_atomic_state *state)
 {
 	struct malidp_plane *mp = to_malidp_plane(plane);
+	int idx;
+
+	if (!drm_dev_enter(plane->dev, &idx))
+		return;
 
 	malidp_hw_clearbits(mp->hwdev,
 			    LAYER_ENABLE | LAYER_FLOWCFG(LAYER_FLOWCFG_MASK),
 			    mp->layer->base + MALIDP_LAYER_CONTROL);
+
+	drm_dev_exit(idx);
 }
 
 static const struct drm_plane_helper_funcs malidp_de_plane_helper_funcs = {
-- 
2.37.3