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SubjectRe: [PATCH] fbdev: Implement simple blanking in pseudocolor modes for vt8500lcdfb
On Wed, Jan 12, 2011 at 23:14, Alexey Charkov <> wrote:
> Implement simple blanking in pseudocolor modes for vt8500lcdfb
> This follows the style of some other in-tree drivers by just setting
> the hardware palette colors to all black. True Color modes are not
> affected, but this at least allows to run xf86-video-fbdev without
> errors due to blanking being unimplemented.

Hmm, I seemed to remember this was handled at the generic level if no .fb_blank
implementation was present? That's why e.g. vesafb and macfb don't
have an fb_blank
implementation, while people run/ran X on them for sure.

[ looking in the code and its history ]

According to full-history-linux, it was removed by:

ommit ca2efeeb715e9fc0f12e57b54ba43ee1e1e50524
Author: Antonino Daplas <>
Date: Sun Nov 7 04:05:04 2004 -0800

[PATCH] fbcon: "Do not touch hardware if vc_mode != KD_TEXT: fix

Sigh, this patch uncovered a can of worms. I tested different combinations,
those with/without xxxfb_blank implementation, framebuffers in directcolor
or truecolor, etc. I find that there is a problem unblanking if the hardware
has no xxxfb_blank() implementation, and also that the generic fb_blank() in
fbmem.c is problematic with drivers in directcolor or pseudocolor mode when
called by an fb application such as X.

Display blanking is implemented in three ways:

1. using the drivers blanking implementation - info->fbops->fb_blank()
2. clearing the screen with the console erase character - fbcon_blank()
3. setting the color map to all black - fb_blank()

The third method is problematic for these reasons:

- Setting the colormap to all black will not work in truecolor mode
- In directcolor or pseudocolor, it will overwrite the fb application's
color map, producing wrong colors.

So, remove the generic implementation in fb_blank() and just return -EINVAL
if there is no hardware implementation. This will be only used by apps doin
an FBIO_BLANK ioctl, and is a more robust approach.

Other changes:

- Consolidated all tests and created an inlined helper function to check if
the framebuffer console is inactive or not.
- fix unblanking if driver has no xxxfb_blank() hook.

I'm probably missing a few more things, but this patch should be generally
correct. Please apply after the entire patch series to avoid rejects.

Signed-off-by: Antonino Daplas <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>


Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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