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@xxxxxxxxx>
---
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
--
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