linux-kernel - Re: [PATCH 1/3] mx3fb: do not support panning with fb blanked

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Message-ID: <CA+8Hj83+Jqv3Bs0mTKYpdsH4ZbOMEQkRpsiCUPVwpeqvWg8jyA@mail.gmail.com>
Date:	Mon, 11 Jun 2012 19:18:00 +0800
From:	Liu Ying <liu.y.victor@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Liu Ying <Ying.Liu@...escale.com>, g.liakhovetski@....de,
	linux-fbdev@...r.kernel.org, FlorianSchandinat@....de,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] mx3fb: do not support panning with fb blanked

2012/6/11, Russell King - ARM Linux <linux@....linux.org.uk>:
> On Mon, Jun 11, 2012 at 06:46:14PM +0800, Liu Ying wrote:
>> 2012/6/11, Russell King - ARM Linux <linux@....linux.org.uk>:
>> > On Mon, Jun 11, 2012 at 09:06:48AM +0800, Liu Ying wrote:
>> >> This patch checks if framebuffer is unblanked before
>> >> we actually trigger panning in custom pan display
>> >> function.
>> >>
>> >> Signed-off-by: Liu Ying <Ying.Liu@...escale.com>
>> >> ---
>> >>  drivers/video/mx3fb.c |    5 +++++
>> >>  1 files changed, 5 insertions(+), 0 deletions(-)
>> >>
>> >> diff --git a/drivers/video/mx3fb.c b/drivers/video/mx3fb.c
>> >> index e3406ab..d53db60 100644
>> >> --- a/drivers/video/mx3fb.c
>> >> +++ b/drivers/video/mx3fb.c
>> >> @@ -1063,6 +1063,11 @@ static int mx3fb_pan_display(struct
>> >> fb_var_screeninfo *var,
>> >>  	dev_dbg(fbi->device, "%s [%c]\n", __func__,
>> >>  		list_empty(&mx3_fbi->idmac_channel->queue) ? '-' : '+');
>> >>
>> >> +	if (mx3_fbi->blank != FB_BLANK_UNBLANK) {
>> >> +		dev_dbg(fbi->device, "panning with fb blanked not supported\n");
>> >> +		return -EFAULT;
>> >> +	}
>> >
>> > Why is this an error, and why return -EFAULT?  What userspace access
>> > failed?
>> >
>> Hi, Russell,
>>
>> IMHO, panning with framebuffer blanked is meaningless, at least, it is
>> not a common usecase.
>
> Yes, but why should anything in userspace care whether the display is
> blanked or not?
>
> For example, we may pan the display when a user program produces output,
> and we're on the last line of the display.  We don't fail that just
> because the screen happens to be blank.  So I don't see why we should
> actively fail an explicit userspace pan request just because the console
> happened to be blanked.
>
> What I'm basically saying is that as far as _userspace_ is concerned,
> all the standard APIs should just work as normal whether the display is
> blanked or not.
>

Ok, understand your point. I am ok to drop this patch.

Thanks.

-- 
Best Regards,
Liu Ying
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