Re: Control fb problem on 8500

Hi all,

On  22 Aug, this message from Michel Dänzer echoed through cyberspace:

quoted

quoted

quoted

I suppose

    if (fix.line_length)
        pScrn->displayWidth = fix.line_length*8/var.bits_per_pixel;
    else
        pScrn->displayWidth = var.xres_virtual;

should work fine, except on hardware were
fix.line_length*8/var.bits_per_pixel might not be integer (e.g. if
1280x1024x24 mode requires a line_length of 4096).

I've thought of this as well. The problem is that the mode hasn't been
initialized when displayWidth is set and used.

So the X server initializes the internal screen structures before it even
knows that it can use them later?

Yes. This really seems to be a rather serious design flaw - the driver is
assumed to know at any time whether it can cope with what the user wants and
how.

Anyway, what do you think about the patch I posted? Michel, can you please try
it?

I'll try to get some time next weekend to do so. I need to get new X
sources (4.0.1), and I need to do that at work rather than via my ISDN
dial-up ;-)

I don't think having to use ShadowFB with the fbdev driver is too bad
because it should generally enhance performance :)

I guess control is the exception. I found out it isn't worth the memory
impact. I once ran a complete x11perf run comparing with and without
shadowfb, and with shadowfb was overall slower. Some operations were
faster, though, but not in general.

I suppose this is because main memory isn't faster on my box than access
to the VRAM. Both are accessed via a 50 MHz bus, and are of the same
basic type (plain old DRAM, that is).

I'll let you know....

Michel

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