linux-kernel - Re: [Linux-fbdev-devel] tty-related oops in latest kernel(s)?

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Message-Id: <1180602278.4570.42.camel@daplas>
Date:	Thu, 31 May 2007 17:04:38 +0800
From:	"Antonino A. Daplas" <adaplas@...il.com>
To:	linux-fbdev-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Tero Roponen <teanropo@....fi>,
	Andy Whitcroft <apw@...dowen.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [Linux-fbdev-devel] tty-related oops in latest kernel(s)?

On Thu, 2007-05-31 at 09:17 +0200, Geert Uytterhoeven wrote:
> On Thu, 31 May 2007, Antonino A. Daplas wrote:
> > On Wed, 2007-05-30 at 22:04 +0400, Alexey Dobriyan wrote:
> > > 2) palette in neofb_par is "u32 palette[16];" which is 4x16 = 64 bytes.
> > >    struct fb_info::pseudo_palette is assigned to it in neo_alloc_fb_info().
> > >    Yet, we check at the beginning of neofb_setcolreg() for color map
> > >    length which neofb advertises as 256 which seems too many.
> > > 
> > 
> > Yes, 256 is too many. the pseudo_palette is used for the 16-color
> > console only.
> > 
> > I'm impressed that this bug has escaped notice for this long. That bug
> > is present since the 2.5.x era.
> > 
> > Probably, the best thing to do is hide the pseudo_palette from the
> > drivers and move it to the console layer where it belongs to spare
> > future driver writers from palette usage confusion. That will be a
> > thankless job.
> 
> The console layer doesn't know how to fill in the pseudo palette in all
> cases, that's why the driver have to do it.
> 

I have actually started working on that.  It involves breaking down
fb_setcolreg() so it deals only with writing to the actual hardware
registers.  The part of fb_setcolreg() that adds entries to the
pseudo_palette can be separated as a new method, fb_get_pixel(), which
given red, blue, green, transp, the driver returns a u32 pixel value
that can be written to the pseudo_palette.

So fbcon can hold a copy of the pseudo_palette and fills it up by
calling info->fbops->fb_get_pixel() successively.

This will touch the logo code, the drawing libraries, each driver, etc
so it's a lot of work.  During the conversion period,  we support having
info->pseudo_palette and fbcon->pseudo_palette at the same time. Once
all drivers are converted, we can remove info->pseudo_palette.

One use for having an fb_get_pixel() method is we can use this as an
rgb888-image-to-raw-framebuffer-format converter.

Currently, I have only converted vesafb. Once the core code is done,
I'll start converting the rest of the drivers one by one.

Tony

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