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Commit 0f16aa0a authored by Tomi Valkeinen's avatar Tomi Valkeinen
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OMAP: DSS2: DSI: use a private workqueue 



Using the shared workqueue led to to a deadlock in the case where the
display was unblanked via keyboard.

What happens is something like this:

- User presses a key

context 1:
- drivers/char/keyboard.c calls schedule_console_callback()
- fb_unblank takes the console semaphore
- dsi bus lock is taken, and frame transfer is started (dsi bus lock is
  left on)
- Unblank code tries to set the panel backlight, which tries to take dsi
  bus lock, but is blocked while the frame transfer is going on

context 2, shared workqueue, console_callback in drivers/char/vt.c:
- Tries to take console semaphore
- Blocks, as console semaphore is being held by context 1
- No other shared workqueue work can be run

context 3, HW irq, caused by FRAMEDONE interrupt:
- Interrupt handler schedules framedone-work in shared workqueue
- Framedone-work is never ran, as the shared workqueue is blocked. This
  means that the unblank thread stays blocked, which means that context 2
  stays blocked.

While I think the real problem is in keyboard/virtual terminal code, using
a private workqueue in the DSI driver is perhaps safer and more robust
than using the shared one. The DSI works should not be delayed more than a
millisecond or so, and even if the private workqueue gives us no hard
promise of doing so, it's still safer bet than the shared workqueue.

Signed-off-by: default avatarTomi Valkeinen <tomi.valkeinen@nokia.com>
parent 86a7867e

drivers/video/omap2/dss/dsi.c

+20 −2
Original line number Diff line number Diff line
@@ -238,6 +238,8 @@ static struct 


	bool te_enabled;



	struct workqueue_struct *workqueue;



	struct work_struct framedone_work;

	void (*framedone_callback)(int, void *);

	void *framedone_data;
@@ -2759,6 +2761,7 @@ static void dsi_update_screen_dispc(struct omap_dss_device *dssdev, 
	unsigned packet_payload;

	unsigned packet_len;

	u32 l;

	int r;

	const unsigned channel = dsi.update_channel;

	/* line buffer is 1024 x 24bits */

	/* XXX: for some reason using full buffer size causes considerable TX
@@ -2809,8 +2812,9 @@ static void dsi_update_screen_dispc(struct omap_dss_device *dssdev, 


	dsi_perf_mark_start();



	schedule_delayed_work(&dsi.framedone_timeout_work,

	r = queue_delayed_work(dsi.workqueue, &dsi.framedone_timeout_work,

			msecs_to_jiffies(250));

	BUG_ON(r == 0);



	dss_start_update(dssdev);
@@ -2841,6 +2845,11 @@ static void dsi_framedone_timeout_work_callback(struct work_struct *work) 


	DSSERR("Framedone not received for 250ms!\n");



	/* XXX While extremely unlikely, we could get FRAMEDONE interrupt after

	 * 250ms which would conflict with this timeout work. What should be

	 * done is first cancel the transfer on the HW, and then cancel the

	 * possibly scheduled framedone work */



	/* SIDLEMODE back to smart-idle */

	dispc_enable_sidle();
@@ -2873,6 +2882,7 @@ static void dsi_framedone_timeout_work_callback(struct work_struct *work) 


static void dsi_framedone_irq_callback(void *data, u32 mask)

{

	int r;

	/* Note: We get FRAMEDONE when DISPC has finished sending pixels and

	 * turns itself off. However, DSI still has the pixels in its buffers,

	 * and is sending the data.
@@ -2881,7 +2891,8 @@ static void dsi_framedone_irq_callback(void *data, u32 mask) 
	/* SIDLEMODE back to smart-idle */

	dispc_enable_sidle();



	schedule_work(&dsi.framedone_work);

	r = queue_work(dsi.workqueue, &dsi.framedone_work);

	BUG_ON(r == 0);

}



static void dsi_handle_framedone(void)
@@ -3292,6 +3303,10 @@ int dsi_init(struct platform_device *pdev) 
	mutex_init(&dsi.lock);

	sema_init(&dsi.bus_lock, 1);



	dsi.workqueue = create_singlethread_workqueue("dsi");

	if (dsi.workqueue == NULL)

		return -ENOMEM;



	INIT_WORK(&dsi.framedone_work, dsi_framedone_work_callback);

	INIT_DELAYED_WORK_DEFERRABLE(&dsi.framedone_timeout_work,

			dsi_framedone_timeout_work_callback);
@@ -3328,6 +3343,7 @@ int dsi_init(struct platform_device *pdev) 
err2:

	iounmap(dsi.base);

err1:

	destroy_workqueue(dsi.workqueue);

	return r;

}
@@ -3335,6 +3351,8 @@ void dsi_exit(void) 
{

	iounmap(dsi.base);



	destroy_workqueue(dsi.workqueue);



	DSSDBG("omap_dsi_exit\n");

}