Patchwork [3/6] drm: tegra: protect DC register access with mutex

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Submitter Lucas Stach
Date Dec. 19, 2012, 9:38 p.m.
Message ID <1355953137-31563-4-git-send-email-dev@lynxeye.de>
Download mbox | patch
Permalink /patch/207522/
State Not Applicable, archived
Headers show

Comments

Lucas Stach - Dec. 19, 2012, 9:38 p.m.
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>
---
We could probably make this a bit more fine grained, but this would add
some complexity and I don't really see a win there for now.
---
 drivers/gpu/drm/tegra/dc.c  | 13 +++++++++++++
 drivers/gpu/drm/tegra/drm.h |  1 +
 2 Dateien geändert, 14 Zeilen hinzugefügt(+)
Mark Zhang - Dec. 20, 2012, 2:36 a.m.
OK, you add a mutex in a tegra_dc structure. But I think there is no
parallel scenario while we operate on a dc. AFAIK, the functions which
you add mutex protection are called by drm sequentially(except for
function "tegra_crtc_load_lut" I'm not very clear about that).

So could you give us an example?

Mark
On 12/20/2012 05:38 AM, Lucas Stach wrote:
> 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>
> ---
> We could probably make this a bit more fine grained, but this would add
> some complexity and I don't really see a win there for now.
> ---
>  drivers/gpu/drm/tegra/dc.c  | 13 +++++++++++++
>  drivers/gpu/drm/tegra/drm.h |  1 +
>  2 Dateien geändert, 14 Zeilen hinzugefügt(+)
> 
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index 54683e4..b256574 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/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);
> diff --git a/drivers/gpu/drm/tegra/drm.h b/drivers/gpu/drm/tegra/drm.h
> index 3a843a7..eae1f56 100644
> --- a/drivers/gpu/drm/tegra/drm.h
> +++ b/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;
>  
> 
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Lucas Stach - Dec. 20, 2012, 8:28 a.m.
Am Donnerstag, den 20.12.2012, 10:36 +0800 schrieb Mark Zhang:
> OK, you add a mutex in a tegra_dc structure. But I think there is no
> parallel scenario while we operate on a dc. AFAIK, the functions which
> you add mutex protection are called by drm sequentially(except for
> function "tegra_crtc_load_lut" I'm not very clear about that).
> 
> So could you give us an example?
> 
You are right, I looked this up again. I thought cursor actions are
async to other modeset actions, but in fact they are also protected by
the mode_config.mutex. So really no need to have another mutex in our dc
code.

Sorry for the noise.

Lucas

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Patch

diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 54683e4..b256574 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/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);
diff --git a/drivers/gpu/drm/tegra/drm.h b/drivers/gpu/drm/tegra/drm.h
index 3a843a7..eae1f56 100644
--- a/drivers/gpu/drm/tegra/drm.h
+++ b/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;