drm: tegra: protect DC register access with mutex

Window properties are programmed through a shared aperture and have to
happen atomically. Also we do the read-update-write dance on some of the
shared regs.
To make sure that different functions don't stumble over each other
protect the register access with a mutex.
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/tegra/dc.c

@@ -171,6 +171,8 @@ static int tegra_crtc_mode_set(struct drm_crtc *crtc,
 		return err;
 	}
 
+	mutex_lock(&dc->regs_mutex);
+
 	/* program display mode */
 	tegra_dc_set_timings(dc, mode);
 
@@ -269,6 +271,8 @@ static int tegra_crtc_mode_set(struct drm_crtc *crtc,
 	tegra_dc_writel(dc, 0xff00, DC_WIN_BLEND_NOKEY);
 	tegra_dc_writel(dc, 0xff00, DC_WIN_BLEND_1WIN);
 
+	mutex_unlock(&dc->regs_mutex);
+
 	return 0;
 }
 
@@ -287,6 +291,8 @@ static void tegra_crtc_prepare(struct drm_crtc *crtc)
 	else
 		syncpt = SYNCPT_VBLANK0;
 
+	mutex_lock(&dc->regs_mutex);
+
 	/* initialize display controller */
 	tegra_dc_writel(dc, 0x00000100, DC_CMD_GENERAL_INCR_SYNCPT_CNTRL);
 	tegra_dc_writel(dc, 0x100 | syncpt, DC_CMD_CONT_SYNCPT_VSYNC);
@@ -320,6 +326,8 @@ static void tegra_crtc_prepare(struct drm_crtc *crtc)
 
 	value = VBLANK_INT | WIN_A_UF_INT | WIN_B_UF_INT | WIN_C_UF_INT;
 	tegra_dc_writel(dc, value, DC_CMD_INT_ENABLE);
+
+	mutex_unlock(&dc->regs_mutex);
 }
 
 static void tegra_crtc_commit(struct drm_crtc *crtc)
@@ -330,6 +338,8 @@ static void tegra_crtc_commit(struct drm_crtc *crtc)
 
 	update_mask = GENERAL_ACT_REQ | WIN_A_ACT_REQ;
 
+	mutex_lock(&dc->regs_mutex);
+
 	tegra_dc_writel(dc, update_mask << 8, DC_CMD_STATE_CONTROL);
 
 	value = tegra_dc_readl(dc, DC_CMD_INT_ENABLE);
@@ -341,6 +351,8 @@ static void tegra_crtc_commit(struct drm_crtc *crtc)
 	tegra_dc_writel(dc, value, DC_CMD_INT_MASK);
 
 	tegra_dc_writel(dc, update_mask, DC_CMD_STATE_CONTROL);
+
+	mutex_unlock(&dc->regs_mutex);
 }
 
 static void tegra_crtc_load_lut(struct drm_crtc *crtc)
@@ -747,6 +759,7 @@ static int tegra_dc_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&dc->list);
+	mutex_init(&dc->regs_mutex);
 	dc->dev = &pdev->dev;
 
 	dc->clk = devm_clk_get(&pdev->dev, NULL);

drivers/gpu/drm/tegra/drm.h

@@ -84,6 +84,7 @@ struct tegra_dc {
 
 	struct clk *clk;
 
+	struct mutex regs_mutex;
 	void __iomem *regs;
 	int irq;