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

On Mon, Jun 11, 2012 at 06:46:14PM +0800, Liu Ying wrote:

2012/6/11, Russell King - ARM Linux [off-list ref]:

quoted

On Mon, Jun 11, 2012 at 09:06:48AM +0800, Liu Ying wrote:

quoted

This patch checks if framebuffer is unblanked before
we actually trigger panning in custom pan display
function.

Signed-off-by: Liu Ying <redacted>
---
 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.