On Friday 16 March 2012 01:05:10 Zhang, Sonic wrote:
> From: Mike Frysinger [mailto:va...@ge...]
>> On Thursday 15 March 2012 23:34:08 Zhang, Sonic wrote:
>>> From: Mike Frysinger [mailto:va...@ge...]
>>>> 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.
>
> How can the application clean the screen before it opens the FB device?
why does it need to be before open ? if the kernel does the memset or
userspace does the memset, the frame still gets cleared.
in looking at the blackfin framebuffer drivers, i'm not sure they're correct. i
don't think the PPI/DMA should be shutdown when the last user space client
closes it. fb_release is for releasing all resources when tearing down the
driver, and fb_blank is runtime management (turning off vsync/hsync and
powering down the screen).
-mike
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