linux-kernel - [PATCH drm-misc-next v2 7/9] drm/fsl-dcu: crtc: protect device resources after removal

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Date:   Sat,  1 Oct 2022 16:58:00 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        mripard@...nel.org, stefan@...er.ch, alison.wang@....com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Danilo Krummrich <dakr@...hat.com>
Subject: [PATCH drm-misc-next v2 7/9] drm/fsl-dcu: crtc: 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/fsl-dcu/fsl_dcu_drm_crtc.c | 37 ++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c
index 1dad90f701c8..c77df9b7893f 100644
--- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c
+++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c
@@ -13,6 +13,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_crtc.h>
+#include <drm/drm_drv.h>
 #include <drm/drm_probe_helper.h>
 #include <drm/drm_vblank.h>
 
@@ -26,6 +27,10 @@ static void fsl_dcu_drm_crtc_atomic_flush(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(dev);
 	struct drm_pending_vblank_event *event = crtc->state->event;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	regmap_write(fsl_dev->regmap,
 		     DCU_UPDATE_MODE, DCU_UPDATE_MODE_READREG);
@@ -40,6 +45,8 @@ static void fsl_dcu_drm_crtc_atomic_flush(struct drm_crtc *crtc,
 			drm_crtc_send_vblank_event(crtc, event);
 		spin_unlock_irq(&crtc->dev->event_lock);
 	}
+
+	drm_dev_exit(idx);
 }
 
 static void fsl_dcu_drm_crtc_atomic_disable(struct drm_crtc *crtc,
@@ -49,6 +56,10 @@ static void fsl_dcu_drm_crtc_atomic_disable(struct drm_crtc *crtc,
 									      crtc);
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(dev);
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	/* always disable planes on the CRTC */
 	drm_atomic_helper_disable_planes_on_crtc(old_crtc_state, true);
@@ -61,6 +72,8 @@ static void fsl_dcu_drm_crtc_atomic_disable(struct drm_crtc *crtc,
 	regmap_write(fsl_dev->regmap, DCU_UPDATE_MODE,
 		     DCU_UPDATE_MODE_READREG);
 	clk_disable_unprepare(fsl_dev->pix_clk);
+
+	drm_dev_exit(idx);
 }
 
 static void fsl_dcu_drm_crtc_atomic_enable(struct drm_crtc *crtc,
@@ -68,6 +81,10 @@ static void fsl_dcu_drm_crtc_atomic_enable(struct drm_crtc *crtc,
 {
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(dev);
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	clk_prepare_enable(fsl_dev->pix_clk);
 	regmap_update_bits(fsl_dev->regmap, DCU_DCU_MODE,
@@ -77,6 +94,8 @@ static void fsl_dcu_drm_crtc_atomic_enable(struct drm_crtc *crtc,
 		     DCU_UPDATE_MODE_READREG);
 
 	drm_crtc_vblank_on(crtc);
+
+	drm_dev_exit(idx);
 }
 
 static void fsl_dcu_drm_crtc_mode_set_nofb(struct drm_crtc *crtc)
@@ -87,6 +106,10 @@ static void fsl_dcu_drm_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	struct drm_display_mode *mode = &crtc->state->mode;
 	unsigned int pol = 0;
 	struct videomode vm;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	clk_set_rate(fsl_dev->pix_clk, mode->clock * 1000);
 
@@ -122,6 +145,8 @@ static void fsl_dcu_drm_crtc_mode_set_nofb(struct drm_crtc *crtc)
 		     DCU_THRESHOLD_LS_BF_VS(BF_VS_VAL) |
 		     DCU_THRESHOLD_OUT_BUF_HIGH(BUF_MAX_VAL) |
 		     DCU_THRESHOLD_OUT_BUF_LOW(BUF_MIN_VAL));
+
+	drm_dev_exit(idx);
 	return;
 }
 
@@ -137,11 +162,17 @@ static int fsl_dcu_drm_crtc_enable_vblank(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(dev);
 	unsigned int value;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return -ENODEV;
 
 	regmap_read(fsl_dev->regmap, DCU_INT_MASK, &value);
 	value &= ~DCU_INT_MASK_VBLANK;
 	regmap_write(fsl_dev->regmap, DCU_INT_MASK, value);
 
+	drm_dev_exit(idx);
+
 	return 0;
 }
 
@@ -150,10 +181,16 @@ static void fsl_dcu_drm_crtc_disable_vblank(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(dev);
 	unsigned int value;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	regmap_read(fsl_dev->regmap, DCU_INT_MASK, &value);
 	value |= DCU_INT_MASK_VBLANK;
 	regmap_write(fsl_dev->regmap, DCU_INT_MASK, value);
+
+	drm_dev_exit(idx);
 }
 
 static const struct drm_crtc_funcs fsl_dcu_drm_crtc_funcs = {
-- 
2.37.3