# Re: \[PATCH\] fb\_defio: add first\_io callback

- From: Heiko Stübner \<heiko@sntech.de\>
- Date: 2012-02-16 07:34:09 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2012/02/13462651
- Thread: https://ratatoskr.run/linux-fbdev/2011/12/13462352/t.md

```text
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:
> > 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
```