[PATCH] fbgen & multiple RGBA

[PATCH] fbgen & multiple RGBA

[Romain Dolbeau]

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Hello,

the attached patch fix a problem with fbgen when changing the
RGBA components but not the depth ; fbgen would not change
the colormap in this case, where it should.

-- 
romain

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Re: [PATCH] fbgen & multiple RGBA

[James Simmons]

> the attached patch fix a problem with fbgen when changing the
> RGBA components but not the depth ; fbgen would not change
> the colormap in this case, where it should.

It would be much easier to use a memcmp.

Re: [Linux-fbdev-devel] Re: [PATCH] fbgen & multiple RGBA

[Romain Dolbeau]

James Simmons wrote:
> 
> > the attached patch fix a problem with fbgen when changing the
> > RGBA components but not the depth ; fbgen would not change
> > the colormap in this case, where it should.
> 
> It would be much easier to use a memcmp.

For the color component, yes, but you can't use a memcmp
on the 'fb_var_screeninfo', as some member of the struct
are irrelevant to colormap switching (you don't want
to reinstall the colormap if only the refresh rate changed,
for instance).

-- 
DOLBEAU Romain               | l'histoire est entierement vraie, puisque
ENS Cachan / Ker Lann        |     je l'ai imaginee d'un bout a l'autre
dolbeau@irisa.fr             |           -- Boris Vian

[PATCH] fbgen & multiple RGBA (w/ memcmp)

[Romain Dolbeau]

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Romain Dolbeau wrote:

> the attached patch fix a problem with fbgen when changing the
> RGBA components but not the depth ; fbgen would not change
> the colormap in this case, where it should.

This is the same patch but using memcmp() on the 3 color
components.

-- 
DOLBEAU Romain               | l'histoire est entierement vraie, puisque
ENS Cachan / Ker Lann        |     je l'ai imaginee d'un bout a l'autre
dolbeau@irisa.fr             |           -- Boris Vian

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Re: [Linux-fbdev-devel] Re: [PATCH] fbgen & multiple RGBA

[James Simmons]

> For the color component, yes, but you can't use a memcmp
> on the 'fb_var_screeninfo', as some member of the struct
> are irrelevant to colormap switching (you don't want
> to reinstall the colormap if only the refresh rate changed,
> for instance).

But it does. If you look at the console code it always calls set_palette
which in turn calls fbcon_set_palette which in turn calls fb_set_cmap. 
This happens every time you VC switch. A few driver writers noticed this
and don't bother with calling fb_Set_var in con_switch but instead a few
pieces of the function. But because of the way the current console system
is designed the colormap will always be set on VC switches.

Re: [Linux-fbdev-devel] Re: [PATCH] fbgen & multiple RGBA

[Romain Dolbeau]

> This happens every time you VC switch.
[snip]
> But because of the way the current console system
> is designed the colormap will always be set on VC switches.

The fix wasn't intended for VC switch, but for any change of
fb_var_screeninfo parameter. Those can happen without VC switching,
that's exactly what 'fbset' is for.

If on your console you do a 'fbset -depth 16 -rgba 5,6,5,0' followed by
a 'fbset -depth 16 -rgba 5,5,5,1' [1], any driver using fbdev will end
up with a crazy colormap because it hasn't been reinstalled after the
RGBA change.

Hence the need for the fix.

[1] yes, in fbset, "-depth" really mean "-bpp" ...

-- 
DOLBEAU Romain               |
ENS Cachan / Ker Lann        | l'histoire est entierement vraie, puisque
Thesard IRISA / CAPS         |     je l'ai imaginee d'un bout a l'autre
dolbeaur@club-internet.fr    |           -- Boris Vian

Re: [Linux-fbdev-devel] Re: [PATCH] fbgen & multiple RGBA

[Romain Dolbeau]

Romain Dolbeau wrote:

> If on your console you do a 'fbset -depth 16 -rgba 5,6,5,0' followed by
> a 'fbset -depth 16 -rgba 5,5,5,1' [1], any driver using fbdev will end
                                                         ^^^^^^^^
That should have been 'fbgen', sorry for the momentary lapse of reason
and the waste of bandwith.

> up with a crazy colormap because it hasn't been reinstalled after the
> RGBA change.

-- 
DOLBEAU Romain               | The Gods made Heavy Metal
ENS Cachan / Ker Lann        |     and it's never gonna die
Thesard IRISA / CAPS         |           -- Manowar
dolbeaur@club-internet.fr    | in 'The Gods made Heavy Metal'