Date: Mon, 29 Nov 2004 11:57:01 -0500
From: Dave Jones <davej@redhat.com>
To: Gerd Knorr <kraxel@bytesex.org>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: MTRR vesafb and wrong X performance
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	Gerd Knorr <kraxel@bytesex.org>, Andrew Morton <akpm@osdl.org>,
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(loony with broken SPF mailfilter removed from Cc)
		
On Mon, Nov 29, 2004 at 05:22:42PM +0100, Gerd Knorr wrote:

 > > vesafb is assuming that the memory used in the current screen mode
 > > xres*yres*depth rounded up to nearest power of 2, is the amount of
 > > ram the card has, which is not just wrong, it's dumb.
 > 
 > It used to do that, but doesn't any more in 2.6.10-rc2.  Check the
 > current code please.

ah, I was looking at a 2.6.9 tree, my apologies.

but..

    if (mtrr) {
        int temp_size = size_total;
        /* Find the largest power-of-two */
        while (temp_size & (temp_size - 1))
                    temp_size &= (temp_size - 1);

                /* Try and find a power of two to add */
        while (temp_size && mtrr_add(vesafb_fix.smem_start, temp_size, MTRR_TYPE_WRCOMB, 1)==-EINVAL) {
            temp_size >>= 1;
        }
    }

size_total is calculated thus:

    size_total = screen_info.lfb_size * 65536;
    if (vram_total)
        size_total = vram_total * 1024 * 1024;
    if (size_total < size_vmode)
        size_total = size_vmode;


where is screen_info.lfb_size set ?

 > > If vesafb can't get it right, maybe it shouldn't be
 > > attempted to do it in the half-assed way it currently does.
 > 
 > Well, 2.6.10-rc1 + newer should get it right now.  We can't do much
 > about BIOS bugs through, other than maybe disabling mtrr by default
 > if too many machines are affected.

or blacklist if there aren't too many perhaps?

		Dave

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