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SubjectRe: [Linux-fbdev-devel] fbmem: is bootup logo broken for monochrome LCD ?
On 11/22/06, James Simmons <jsimmons@infradead.org> wrote:
> 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.

/* write trailing bits */
if (shift) {
u32 end_mask = (~(u32)0 << shift);

val = FB_READL(dst1);
val &= end_mask;
FB_WRITEL(val, dst1);
}

Another thing is that I don't see how very small images (for example
when image->width = 4) will be handled.

> > > /* Did the bitshift spill bits to the next long? */
> > > if (shift >= 31) {
> > > FB_WRITEL(val, dst++);
> > > val = (shift == 31) ? 0 :(color >> (32 - shift));
> > > }
> > > shift += 1;
> > > shift &= (32 - 1);
> > > }
> > >
> > > [ ...]
>
> Let me know if that works.

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 ?

--
Franck
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