[Intel-gfx] G45 BIOS mis-initializes stolen GTT PTEs

[Martin Olsson]

I don't have time to do extensive testing right now but I did apply the intel-agp patch, built the
new module and yes am I able to boot into EXA without freeze at login. So far this seems like exactly
the fix that I needed. Further, it also seems that this fixes the "crash when launching the GIMP or
OpenOffice in XAA mode" for me.

Thanks a lot to everyone who worked on this! I'm looking forward to seeing something like this land in .28


Martin


Keith Packard wrote:
> Ok, so I've managed to get my G45 running without DRI.
> 
> What I discovered is that the very last PTE for stolen memory (pages
> allocated by the BIOS for graphics use) was not initialized by the BIOS
> correctly. When the graphics hardware tried to access that page, it
> would get a segfault and lock up until it was reset.
> 
> Here's a patch which finds that PTE and fixes it if it is broken. If
> your G45 is crashing randomly after startup, please give this patch a
> try and see if it works.
> 
> As you can see, it's an ugly hack that doesn't check to make sure you're
> running on a G45, so it's not exactly ready for upstream, but it should
> detect and repair this specific bug.
> 
> From f4867dee03bfd3edb05f1fcccfe34eba209f6af7 Mon Sep 17 00:00:00 2001
> From: Keith Packard <keithp at keithp.com>
> Date: Mon, 13 Oct 2008 23:35:55 -0700
> Subject: [PATCH] Check and repair the last stolen GTT entry for Intel G45 motherboards
> 
> At least one existing G45 motherboard BIOS mis-initializes the GTT entries
> for stolen memory leaving the last PTE invalid. Detect this case and patch
> it up to point at the page after the previous PTE.
> 
> Signed-off-by: Keith Packard <keithp at keithp.com>
> ---
>  drivers/char/agp/intel-agp.c |   20 ++++++++++++++++++++
>  1 files changed, 20 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
> index a6a0c34..32ea05e 100644
> --- a/drivers/char/agp/intel-agp.c
> +++ b/drivers/char/agp/intel-agp.c
> @@ -987,6 +987,26 @@ static int intel_i915_configure(void)
>  	readl(intel_private.registers+I810_PGETBL_CTL);	/* PCI Posting. */
>  
>  	if (agp_bridge->driver->needs_scratch_page) {
> +		u32 gtt;
> +		for (i = 0; i < intel_private.gtt_entries; i++) {
> +			gtt = readl(intel_private.gtt+i);
> +			if ((gtt & I810_PTE_VALID) == 0)
> +				dev_printk(KERN_ERR, &intel_private.pcidev->dev,
> +					   "invalid stolen PTE %08x = %08x\n",
> +					   i, gtt);
> +		}
> +		i = intel_private.gtt_entries - 1;
> +		gtt = readl(intel_private.gtt + i);
> +		if ((gtt & I810_PTE_VALID) == 0) {
> +			gtt = readl(intel_private.gtt + (i-1));
> +			if (gtt & I810_PTE_VALID) {
> +				gtt += 0x1000;
> +				dev_printk(KERN_ERR, &intel_private.pcidev->dev,
> +					   "patching stolen PTE %08x to %08x\n",
> +					   i, gtt);
> +				writel(gtt, intel_private.gtt+i);
> +			}
> +		}
>  		for (i = intel_private.gtt_entries; i < current_size->num_entries; i++) {
>  			writel(agp_bridge->scratch_page, intel_private.gtt+i);
>  		}
> 
> 
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