[PATCH v2 0/5] drm/tilcdc: Fix cpufreq transition related race + cleanup

[PATCH v2 0/5] drm/tilcdc: Fix cpufreq transition related race + cleanup

[Jyri Sarha]

Changes since v1:
- Use drm_modeset_lock/unlock_crtc() instead of taking mode config mutex
- Rewrote decsription for old "drm/tilcdc: Add tilcdc_crtc_set_clk() and
  cleanup cpufreq_transition()" which now called "drm/tilcdc: Clean up LCDC
  functional clock rate setting code"
- Dropped "drm/tilcdc: Add mutex to protect crtc enable and disable routines"
- Added "drm/tilcdc: Flush flip-work workqueue before drm_flip_work_cleanup()"
- Added "drm/tilcdc: Remove unnecessary tilcdc_crtc_disable() from
  	 tilcdc_unload()"
- Added "drm/tilcdc: WARN if CRTC is touched without CRTC lock"

There was a race between mode_set_nofb() and cpufreq_transition()
calling tilcdc_crtc_update_clk() without locking.

The first patch fixes the race in with a minimal change by taking
the drm CRTC lock for the duration of the clock update.

The second patch goes a step forward and cleans up the clock setting
code a bit.

BR,
Jyri


Jyri Sarha (5):
  drm/tilcdc: Take crtc modeset lock while updating the crtc clock rate
  drm/tilcdc: Clean up LCDC functional clock rate setting code
  drm/tilcdc: Flush flip-work workqueue before drm_flip_work_cleanup()
  drm/tilcdc: Remove unnecessary tilcdc_crtc_disable() from
    tilcdc_unload()
  drm/tilcdc: WARN if CRTC is touched without CRTC lock

 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 91 +++++++++++++++++++++++-------------
 drivers/gpu/drm/tilcdc/tilcdc_drv.c  | 12 ++---
 drivers/gpu/drm/tilcdc/tilcdc_drv.h  |  1 -
 3 files changed, 62 insertions(+), 42 deletions(-)

-- 
1.9.1

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[PATCH v2 1/5] drm/tilcdc: Take crtc modeset lock while updating the crtc clock rate

[Jyri Sarha]

Take crtc modeset lock while updating the crtc clock rate. To avoid a
race in tilcdc_crtc_update_clk(), we do not want crtc mode to change
while we update crtc clock.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_drv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
index f8892e9..b1ac61e 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
@@ -184,10 +184,13 @@ static int cpufreq_transition(struct notifier_block *nb,
 {
 	struct tilcdc_drm_private *priv = container_of(nb,
 			struct tilcdc_drm_private, freq_transition);
+
 	if (val == CPUFREQ_POSTCHANGE) {
 		if (priv->lcd_fck_rate != clk_get_rate(priv->clk)) {
+			drm_modeset_lock_crtc(priv->crtc, NULL);
 			priv->lcd_fck_rate = clk_get_rate(priv->clk);
 			tilcdc_crtc_update_clk(priv->crtc);
+			drm_modeset_unlock_crtc(priv->crtc);
 		}
 	}
 
-- 
1.9.1

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[PATCH v2 2/5] drm/tilcdc: Clean up LCDC functional clock rate setting code

[Jyri Sarha]

Clean up LCDC functional clock rate seating code.

The LCDC functional clock is set by two functions: mode_set_nofb() and
cpufreq_transition().

When tilcdc_crtc_mode_set_nofb() is called in atomic commit phase the
drm atomic helpers have taken all the necessary drm locks and turned
off the crtc, while tilcdc_commit() is keeping LCDC powered on. For
mode_set_nofb() just a simple clock setting function without any
locking or power management code is enough. The new tilcdc_crtc_set_clk()
is implemented for that purpose.

cpufreq_transition() on the other hand is called from outside DRM and
it needs to take the necessary locks and turn off the CRTC while
keeping the LCDC powered. The reimplemented tilcdc_crtc_update_clk()
is for that purpose and it uses the new tilcdc_crtc_set_clk() to
actually set the clock.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 77 +++++++++++++++++++++---------------
 drivers/gpu/drm/tilcdc/tilcdc_drv.c  | 11 +-----
 drivers/gpu/drm/tilcdc/tilcdc_drv.h  |  1 -
 3 files changed, 47 insertions(+), 42 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 84b36fd..f4e6a5b 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -35,6 +35,8 @@ struct tilcdc_crtc {
 	bool frame_done;
 	spinlock_t irq_lock;
 
+	unsigned int lcd_fck_rate;
+
 	ktime_t last_vblank;
 
 	struct drm_framebuffer *curr_fb;
@@ -324,6 +326,37 @@ static bool tilcdc_crtc_mode_fixup(struct drm_crtc *crtc,
 	return true;
 }
 
+static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
+{
+	struct drm_device *dev = crtc->dev;
+	struct tilcdc_drm_private *priv = dev->dev_private;
+	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
+	const unsigned clkdiv = 2; /* using a fixed divider of 2 */
+	int ret;
+
+	/* mode.clock is in KHz, set_rate wants parameter in Hz */
+	ret = clk_set_rate(priv->clk, crtc->mode.clock * 1000 * clkdiv);
+	if (ret < 0) {
+		dev_err(dev->dev, "failed to set display clock rate to: %d\n",
+			crtc->mode.clock);
+		return;
+	}
+
+	tilcdc_crtc->lcd_fck_rate = clk_get_rate(priv->clk);
+
+	DBG("lcd_clk=%u, mode clock=%d, div=%u",
+	    tilcdc_crtc->lcd_fck_rate, crtc->mode.clock, clkdiv);
+
+	/* Configure the LCD clock divisor. */
+	tilcdc_write(dev, LCDC_CTRL_REG, LCDC_CLK_DIVISOR(clkdiv) |
+		     LCDC_RASTER_MODE);
+
+	if (priv->rev == 2)
+		tilcdc_set(dev, LCDC_CLK_ENABLE_REG,
+				LCDC_V2_DMA_CLK_EN | LCDC_V2_LIDD_CLK_EN |
+				LCDC_V2_CORE_CLK_EN);
+}
+
 static void tilcdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 {
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
@@ -486,7 +519,7 @@ static void tilcdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 
 	set_scanout(crtc, fb);
 
-	tilcdc_crtc_update_clk(crtc);
+	tilcdc_crtc_set_clk(crtc);
 
 	crtc->hwmode = crtc->state->adjusted_mode;
 }
@@ -655,41 +688,21 @@ void tilcdc_crtc_update_clk(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
-	unsigned long lcd_clk;
-	const unsigned clkdiv = 2; /* using a fixed divider of 2 */
-	int ret;
+	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
 
-	pm_runtime_get_sync(dev->dev);
+	drm_modeset_lock_crtc(crtc, NULL);
+	if (tilcdc_crtc->lcd_fck_rate != clk_get_rate(priv->clk)) {
+		if (tilcdc_crtc_is_on(crtc)) {
+			pm_runtime_get_sync(dev->dev);
+			tilcdc_crtc_disable(crtc);
 
-	tilcdc_crtc_disable(crtc);
+			tilcdc_crtc_set_clk(crtc);
 
-	/* mode.clock is in KHz, set_rate wants parameter in Hz */
-	ret = clk_set_rate(priv->clk, crtc->mode.clock * 1000 * clkdiv);
-	if (ret < 0) {
-		dev_err(dev->dev, "failed to set display clock rate to: %d\n",
-				crtc->mode.clock);
-		goto out;
+			tilcdc_crtc_enable(crtc);
+			pm_runtime_put_sync(dev->dev);
+		}
 	}
-
-	lcd_clk = clk_get_rate(priv->clk);
-
-	DBG("lcd_clk=%lu, mode clock=%d, div=%u",
-		lcd_clk, crtc->mode.clock, clkdiv);
-
-	/* Configure the LCD clock divisor. */
-	tilcdc_write(dev, LCDC_CTRL_REG, LCDC_CLK_DIVISOR(clkdiv) |
-			LCDC_RASTER_MODE);
-
-	if (priv->rev == 2)
-		tilcdc_set(dev, LCDC_CLK_ENABLE_REG,
-				LCDC_V2_DMA_CLK_EN | LCDC_V2_LIDD_CLK_EN |
-				LCDC_V2_CORE_CLK_EN);
-
-	if (tilcdc_crtc_is_on(crtc))
-		tilcdc_crtc_enable(crtc);
-
-out:
-	pm_runtime_put_sync(dev->dev);
+	drm_modeset_unlock_crtc(crtc);
 }
 
 #define SYNC_LOST_COUNT_LIMIT 50
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
index b1ac61e..52ff3e1 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
@@ -185,14 +185,8 @@ static int cpufreq_transition(struct notifier_block *nb,
 	struct tilcdc_drm_private *priv = container_of(nb,
 			struct tilcdc_drm_private, freq_transition);
 
-	if (val == CPUFREQ_POSTCHANGE) {
-		if (priv->lcd_fck_rate != clk_get_rate(priv->clk)) {
-			drm_modeset_lock_crtc(priv->crtc, NULL);
-			priv->lcd_fck_rate = clk_get_rate(priv->clk);
-			tilcdc_crtc_update_clk(priv->crtc);
-			drm_modeset_unlock_crtc(priv->crtc);
-		}
-	}
+	if (val == CPUFREQ_POSTCHANGE)
+		tilcdc_crtc_update_clk(priv->crtc);
 
 	return 0;
 }
@@ -286,7 +280,6 @@ static int tilcdc_load(struct drm_device *dev, unsigned long flags)
 	}
 
 #ifdef CONFIG_CPU_FREQ
-	priv->lcd_fck_rate = clk_get_rate(priv->clk);
 	priv->freq_transition.notifier_call = cpufreq_transition;
 	ret = cpufreq_register_notifier(&priv->freq_transition,
 			CPUFREQ_TRANSITION_NOTIFIER);
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.h b/drivers/gpu/drm/tilcdc/tilcdc_drv.h
index a6e5e6d..9780c37 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.h
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.h
@@ -74,7 +74,6 @@ struct tilcdc_drm_private {
 
 #ifdef CONFIG_CPU_FREQ
 	struct notifier_block freq_transition;
-	unsigned int lcd_fck_rate;
 #endif
 
 	struct workqueue_struct *wq;
-- 
1.9.1

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[PATCH v2 3/5] drm/tilcdc: Flush flip-work workqueue before drm_flip_work_cleanup()

[Jyri Sarha]

Flush flip-work workqueue before drm_flip_work_cleanup(). It causes a
nasty warning if there is unfinished flip-work in the queue when
drm_flip_work_cleanup() is called. The flush_workqueue() has to be
called before drm_crtc_cleanup() for unref_worker() to be able to do
its job.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index f4e6a5b..6974624 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -18,6 +18,7 @@
 #include "drm_flip_work.h"
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_atomic_helper.h>
+#include <linux/workqueue.h>
 
 #include "tilcdc_drv.h"
 #include "tilcdc_regs.h"
@@ -247,9 +248,12 @@ out:
 static void tilcdc_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
+	struct tilcdc_drm_private *priv = crtc->dev->dev_private;
 
 	tilcdc_crtc_disable(crtc);
 
+	flush_workqueue(priv->wq);
+
 	of_node_put(crtc->port);
 	drm_crtc_cleanup(crtc);
 	drm_flip_work_cleanup(&tilcdc_crtc->unref_work);
-- 
1.9.1

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[PATCH v2 4/5] drm/tilcdc: Remove unnecessary tilcdc_crtc_disable() from tilcdc_unload()

[Jyri Sarha]

Remove unnecessary tilcdc_crtc_disable() from tilcdc_unload(). The
tilcdc_crtc_disable() called via tilcdc_crtc_destroy() by
drm_mode_config_cleanup() couple of lines later.

The early call to tilcdc_crtc_disable() was a wrong fix (that worked)
for calling drm_flip_work_cleanup() before flushing the flip-work
queue.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_drv.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
index 52ff3e1..1981ae9 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
@@ -200,8 +200,6 @@ static int tilcdc_unload(struct drm_device *dev)
 {
 	struct tilcdc_drm_private *priv = dev->dev_private;
 
-	tilcdc_crtc_disable(priv->crtc);
-
 	tilcdc_remove_external_encoders(dev);
 
 	drm_fbdev_cma_fini(priv->fbdev);
-- 
1.9.1

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[PATCH v2 5/5] drm/tilcdc: WARN if CRTC is touched without CRTC lock

[Jyri Sarha]

WARN if CRTC is touched without CRTC lock. The crtc functions should
not be called simultaneously from multiple threads. Having the DRM
CRTC lock should take care of that.

tilcdc_crtc_destroy() has to take the CRTC lock befor calling
tilcdc_crtc_disable() because drm_mode_config_cleanup() does not take
the lock. If this ever changes the CRTC locking has to be removed from
tilcdc_crtc_destroy().

Signed-off-by: Jyri Sarha <jsarha@ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 6974624..94a78e2 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -154,6 +154,8 @@ static void tilcdc_crtc_enable(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
 
+	WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
+
 	if (tilcdc_crtc->enabled)
 		return;
 
@@ -178,6 +180,8 @@ void tilcdc_crtc_disable(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
 
+	WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
+
 	if (!tilcdc_crtc->enabled)
 		return;
 
@@ -250,7 +254,9 @@ static void tilcdc_crtc_destroy(struct drm_crtc *crtc)
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
 	struct tilcdc_drm_private *priv = crtc->dev->dev_private;
 
+	drm_modeset_lock_crtc(crtc, NULL);
 	tilcdc_crtc_disable(crtc);
+	drm_modeset_unlock_crtc(crtc);
 
 	flush_workqueue(priv->wq);
 
@@ -267,6 +273,8 @@ int tilcdc_crtc_update_fb(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	unsigned long flags;
 
+	WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
+
 	if (tilcdc_crtc->event) {
 		dev_err(dev->dev, "already pending page flip!\n");
 		return -EBUSY;
@@ -371,6 +379,8 @@ static void tilcdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
 	struct drm_framebuffer *fb = crtc->primary->state->fb;
 
+	WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
+
 	if (WARN_ON(!info))
 		return;
 
-- 
1.9.1

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Re: [PATCH v2 5/5] drm/tilcdc: WARN if CRTC is touched without CRTC lock

[Tomi Valkeinen]

[-- Attachment #1.1.1: Type: text/plain, Size: 606 bytes --]

On 06/09/16 23:59, Jyri Sarha wrote:
> WARN if CRTC is touched without CRTC lock. The crtc functions should
> not be called simultaneously from multiple threads. Having the DRM
> CRTC lock should take care of that.
> 
> tilcdc_crtc_destroy() has to take the CRTC lock befor calling
> tilcdc_crtc_disable() because drm_mode_config_cleanup() does not take
> the lock. If this ever changes the CRTC locking has to be removed from
> tilcdc_crtc_destroy().

Shouldn't these be two separate patches? This one is (according to
subject) adding WARNs, but it is actually also adding locking.

 Tomi


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