Re: [PATCH] [#7001] framebuffer: old image of last app would retain for a while after starting new app

-----Original Message-----
From: Mike Frysinger [mailto:[email protected]]
Sent: Friday, March 16, 2012 11:55 AM
To: Zhang, Sonic
Cc: uclinux-dist-devel-ZG0+EudsQA8dtHy/[email protected]; Wu, Aaron; linux-fbdev-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: [PATCH] [#7001] framebuffer: old image of last app would retain for a while after starting new app

On Thursday 15 March 2012 23:34:08 Zhang, Sonic wrote:
> From: Mike Frysinger [mailto:[email protected]]
>> On Thursday 15 March 2012 05:23:50 Wu, Aaron wrote:
>> > Old image of last application would retain for a while when
>> > starting a new application, this patch clear the frambuffer before
>> > displaying every time the fb is opened.
>>
>> i'm not sure the behavior you describe is wrong.  in fact, i'm pretty
>> sure it sounds correct.  if an app writes an image to the framebuffer
>> and then quits, that image should stay there indefinitely until
>> something else opens the framebuffer and draws their own image.
>
> Before the second application draws its own image, the image of last
> application has already been displayed on the LCD when the second
> application opens the FB device(PPI is enabled when it is opened).
> This is not a correct behavior.

sure it is.  if the app wants to clear the screen, it can do so.  generally it's going to anyways by drawing an entire frame.  having the frame buffer driver always clear the screen introduces wasted memory overhead as it does the memset(), and user-visible jank as the device transitions from an initial splash screen to the main userspace app.

this is a policy decision that doesn't really belong in kernel space.  and if it did, it should be agreed upon by all frame buffer users and not just changing a few drivers.
-mike

How can the application clean the screen before it opens the FB device?

Sonic