Re: DRMKMS problem on i386 i915 chipset

[Mike Pumford <mpumford%black-star.demon.co.uk@localhost>]

Martin Neitzel wrote:
> > Having a problem getting a 7-BETA KMS kernel to work on my now quite old
> > Sony VAIO laptop.
>
> Hey, at least you can **see** some dmesg output :-)
>
> For me (attempting my very first -current installation), the kernel
> from seven or ten days ago fails with blanking the screen.
>
> Just prior to that, it manages to dump some registers/memory/device
> table to the screen.  The blanking (perhaps even panicing?) happens
> too fast to let me read anything, though.
>
> This is the i386 port on an ASUS EeePc 1000H, Atom N270 with Intel
> 945GME graphics.  (Works just fine with Netbsd-5.x and -6.x, incl. drm)
>
> is very helpful to me because it provides a few suggestions for disabling
> drivers at userconf stage.
That worked for me. I did:
disable i915drmkms

Which got me a kernel that booted in textmode.

However I've now done some further debugging and I now have a working 
system with DRMKMS enabled including 3D accelleration in X.

The critical failure in my system was the fact that the DRM driver 
couldn't map the VGA BIOS to get parameters from it. The reason for this 
failure turned out to be a piece of memory called the flush page 
allocated in the i810 AGP driver. The kernel was creating the mapping 
for this at 0xc0000->0xc0fff which is the first page of the VGA BIOS. 
Whether this page needs to be allocated or not depends on the system 
BIOS so it explains why DRMKMS would work for some people on i915 
systems and not others.

To fix this I made the mod described in the attached patch to the AGP 
driver so that it won't accept an allocation for this page in the first 
1MB of memory to avoid the BIOS pages. No idea if this patch will fix it 
for others but perhaps it will. :)

Mike


Index: agp_i810.c
===================================================================
RCS file: /cvsroot/src/sys/dev/pci/agp_i810.c,v
retrieving revision 1.112.2.2
diff -u -r1.112.2.2 agp_i810.c
--- agp_i810.c	17 Mar 2015 17:52:49 -0000	1.112.2.2
+++ agp_i810.c	3 Apr 2015 20:53:41 -0000
@@ -646,7 +646,7 @@
 		minaddr = PAGE_SIZE;	/* XXX PCIBIOS_MIN_MEM?  */
 		maxaddr = MIN(UINT64_MAX, ~(bus_addr_t)0);
 	}
-
+	minaddr = 0x100000; /* Stay out of ISA mem/BIOS area */
 	/* Allocate or map a pre-allocated a page for it.  */
 	if (ISSET(addr, 1)) {
 		/* BIOS allocated it for us.  Use that.  */