linux-kernel - Re: [Linux-fbdev-devel] fbmem: is bootup logo broken for monochrome LCD ?

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Date:	Mon, 27 Nov 2006 16:01:21 +0000 (GMT)
From:	James Simmons <jsimmons@...radead.org>
To:	Franck Bui-Huu <vagabon.xyz@...il.com>
cc:	Andrew Morton <akpm@...l.org>,
	Linux Fbdev development list 
	<linux-fbdev-devel@...ts.sourceforge.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-fbdev-devel] fbmem: is bootup logo broken for monochrome
 LCD ?


> > Replace the below line in my patch I sent
> > 
> > > >                     val |= color << shift;
> > 
> > with
> >                         val <<= shift;
> >                         val |= color;
> 
> I think it can't work since shift is 0 to 31, you'll end up with 'val
> <<= 31' which I don't think is what you want.
 
> doing
>                         val <<= 1;
> 
> make it works but it's still very fragile. Code which deals with
> trailing bit seems bogus since new value of 'val' is simply discarded
> here.

I'm going to test the code in depth over the next few days. I managed to 
fix most of the problems with fast_imageblit. Now to fix the slow image 
blit code.

> I'm wondering if working with 32 bits words really worth... I mean the
> code is quite hard to follow because it needs to deal with endianess,
> heading bits, trailings bits whereas working with 8 bits would be so
> much easier, wouldn't it ? Are writings in video RAM very long ?

Yes. We need to minimize the writes over the PCI bus. Its really really 
slow.
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