[PATCH] fb_defio: add first_io callback

With this optional callback the driver is notified when the first page
is entered into the pagelist and a new deferred_io call is scheduled.

A possible use-case for this is runtime-pm. In the first_io call
	pm_runtime_get()
could be called, which starts an asynchronous runtime_resume of the
device. In the deferred_io callback a call to
	pm_runtime_barrier()
makes the sure, the device is resumed by then and a
	pm_runtime_put()
may put the device back to sleep.

Also, some SoCs may use the runtime-pm system to determine if they
are able to enter deeper idle states. Therefore it is necessary to
keep the use-count from the first written page until the conclusion
of the screen update, to prevent the system from going to sleep before
completing the pending update.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
 drivers/video/fb_defio.c |    4 ++++
 include/linux/fb.h       |    1 +
 2 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index c27e153..070f26f 100644
--- a/drivers/video/fb_defio.c
+++ b/drivers/video/fb_defio.c

@@ -107,6 +107,10 @@ static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
 	/* protect against the workqueue changing the page list */
 	mutex_lock(&fbdefio->lock);
 
+	/* first write in this cycle, notify the driver */
+	if (fbdefio->first_io && list_empty(&fbdefio->pagelist))
+		fbdefio->first_io(info);
+
 	/*
 	 * We want the page to remain locked from ->page_mkwrite until
 	 * the PTE is marked dirty to avoid page_mkclean() being called

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 1d6836c..b86cd41 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h

@@ -602,6 +602,7 @@ struct fb_deferred_io {
 	struct mutex lock; /* mutex that protects the page list */
 	struct list_head pagelist; /* list of touched pages */
 	/* callback */
+	void (*first_io)(struct fb_info *info);
 	void (*deferred_io)(struct fb_info *info, struct list_head *pagelist);
 };
 #endif

-- 
1.7.2.3

Hi Heiko,

sorry for the long delay.

On 12/31/2011 10:45 AM, Heiko Stübner wrote:

With this optional callback the driver is notified when the first page
is entered into the pagelist and a new deferred_io call is scheduled.

A possible use-case for this is runtime-pm. In the first_io call
	pm_runtime_get()
could be called, which starts an asynchronous runtime_resume of the
device. In the deferred_io callback a call to
	pm_runtime_barrier()
makes the sure, the device is resumed by then and a
	pm_runtime_put()
may put the device back to sleep.

Also, some SoCs may use the runtime-pm system to determine if they
are able to enter deeper idle states. Therefore it is necessary to
keep the use-count from the first written page until the conclusion
of the screen update, to prevent the system from going to sleep before
completing the pending update.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>

while I consider this patch acceptable, I don't see any reason to apply it as
long as there is no driver actually using it.


Best regards,

Florian Tobias Schandinat

Hi Florian,

Am Donnerstag, 16. Februar 2012, 03:27:25 schrieb Florian Tobias Schandinat:

Hi Heiko,

sorry for the long delay.

no problem

On 12/31/2011 10:45 AM, Heiko Stübner wrote:

quoted

With this optional callback the driver is notified when the first page
is entered into the pagelist and a new deferred_io call is scheduled.

A possible use-case for this is runtime-pm. In the first_io call

	pm_runtime_get()

could be called, which starts an asynchronous runtime_resume of the
device. In the deferred_io callback a call to

	pm_runtime_barrier()

makes the sure, the device is resumed by then and a

	pm_runtime_put()

may put the device back to sleep.

Also, some SoCs may use the runtime-pm system to determine if they
are able to enter deeper idle states. Therefore it is necessary to
keep the use-count from the first written page until the conclusion
of the screen update, to prevent the system from going to sleep before
completing the pending update.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>

while I consider this patch acceptable, I don't see any reason to apply it
as long as there is no driver actually using it.

ok, so I will keep sitting on it until my driver for the AUO-K190x epd 
controller is ready for primetime and resubmit this patch in conjunction with 
it.

Heiko