The last few revisions of the kernel (the only 2.6 kernels I've used)
are setting up my MTRR ranges sub-optimally.
This is on a notebook machine which "features" the use of system RAM
in place of dedicated video memory. Currently a 32MB portion of the
system memory is carved out for the display. The system memory
consists of 2 512MB SODIMM modules. These are my system devices:
# lspci
00:00.0 Host bridge: ATI Technologies Inc RS200/RS200M AGP Bridge [IGP 340M] (rev 02)
00:01.0 PCI bridge: ATI Technologies Inc PCI Bridge [IGP 340M]
00:06.0 Multimedia audio controller: ALi Corporation M5451 PCI AC-Link Controller Audio Device (rev 02)
00:07.0 ISA bridge: ALi Corporation M1533 PCI to ISA Bridge [Aladdin IV]
00:08.0 Modem: ALi Corporation M5457 AC'97 Modem Controller
00:09.0 Network controller: Broadcom Corporation BCM4306 802.11b/g Wireless LAN Controller (rev 02)
00:0a.0 CardBus bridge: O2 Micro, Inc. OZ6912 Cardbus Controller
00:0b.0 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 50)
00:0b.1 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 50)
00:0b.2 USB Controller: VIA Technologies, Inc. USB 2.0 (rev 51)
00:0c.0 FireWire (IEEE 1394): Texas Instruments TSB43AB21 IEEE-1394a-2000 Controller (PHY/Link)
00:10.0 IDE interface: ALi Corporation M5229 IDE (rev c4)
00:11.0 Bridge: ALi Corporation M7101 Power Management Controller [PMU]
00:12.0 Ethernet controller: National Semiconductor Corporation DP83815 (MacPhyter) Ethernet Controller
01:05.0 VGA compatible controller: ATI Technologies Inc Radeon IGP 340M
And this is how the MTRRs are set up after booting the 2.6.8 kernel:
# cat /proc/mtrr
reg00: base=0x00000000 ( 0MB), size= 512MB: write-back, count=1
reg01: base=0x20000000 ( 512MB), size= 256MB: write-back, count=1
reg02: base=0x30000000 ( 768MB), size= 128MB: write-back, count=1
reg03: base=0x38000000 ( 896MB), size= 64MB: write-back, count=1
reg04: base=0x3c000000 ( 960MB), size= 32MB: write-back, count=1
reg05: base=0x3df80000 ( 991MB), size= 512KB: uncachable, count=1
reg06: base=0x4df80000 (1247MB), size= 512KB: uncachable, count=1
reg07: base=0xdc000000 (3520MB), size= 1MB: write-combining, count=1
With this configuration, Xorg (v6.8.1) logs this complaint at startup:
(WW) RADEON(0): Failed to set up write-combining range (0xdc000000,0x2000000)
I can satisfy this complaint by manually adjusting the MTRR config
prior to starting Xorg like this:
echo "disable=7" >| /proc/mtrr
echo "base=0xdc000000 size=0x2000000 type=write-combining" > /proc/mtrr
This gets me the following config:
# cat /proc/mtrr
reg00: base=0x00000000 ( 0MB), size= 512MB: write-back, count=1
reg01: base=0x20000000 ( 512MB), size= 256MB: write-back, count=1
reg02: base=0x30000000 ( 768MB), size= 128MB: write-back, count=1
reg03: base=0x38000000 ( 896MB), size= 64MB: write-back, count=1
reg04: base=0x3c000000 ( 960MB), size= 32MB: write-back, count=1
reg05: base=0x3df80000 ( 991MB), size= 512KB: uncachable, count=1
reg06: base=0x4df80000 (1247MB), size= 512KB: uncachable, count=1
reg07: base=0xdc000000 (3520MB), size= 32MB: write-combining, count=1
My BIOS allows me to configure the amount of system memory reserved
for video use. I've tried various values (trying to balance the size
and location of the reserved area) but in the end only manually
adjusting the MTRR values will prevent the Xorg complaint.
Look at that the default MTRR config again. Register 7 is configured
for a 1MB area. One megabyte? That strikes me as being sub-optimal.
What, if anything, can I do have the kernel configure my MTRRs more
effectively?
Thanks.
On Thu, Sep 23, 2004 at 09:53:36AM -0500, Steve Snyder wrote:
>
> And this is how the MTRRs are set up after booting the 2.6.8 kernel:
>
> # cat /proc/mtrr
> reg00: base=0x00000000 ( 0MB), size= 512MB: write-back, count=1
> reg01: base=0x20000000 ( 512MB), size= 256MB: write-back, count=1
> reg02: base=0x30000000 ( 768MB), size= 128MB: write-back, count=1
> reg03: base=0x38000000 ( 896MB), size= 64MB: write-back, count=1
> reg04: base=0x3c000000 ( 960MB), size= 32MB: write-back, count=1
> reg05: base=0x3df80000 ( 991MB), size= 512KB: uncachable, count=1
> reg06: base=0x4df80000 (1247MB), size= 512KB: uncachable, count=1
> reg07: base=0xdc000000 (3520MB), size= 1MB: write-combining, count=1
That last MTRR is created by the vesafb. It doesn't size video memory,
but instead creates an MTRR big enough to cover xresolution * yresolution * depth
and then rounds down to the nearest alignment that is allowed for MTRRs.
(in your case 1MB).
> With this configuration, Xorg (v6.8.1) logs this complaint at startup:
>
> (WW) RADEON(0): Failed to set up write-combining range (0xdc000000,0x2000000)
X sized the video memory, and has a better idea of what is going on.
In an ideal world, X could fix up suboptimal MTRR setups like this
by deleting the existing range.
Another way of working around it is to tell the vesafb not to set up an
mtrr at all. There is a boot command line option to tell it to do this iirc.
> I can satisfy this complaint by manually adjusting the MTRR config
> prior to starting Xorg like this:
>
> echo "disable=7" >| /proc/mtrr
> echo "base=0xdc000000 size=0x2000000 type=write-combining" > /proc/mtrr
X should also do the right thing without the second command.
With MTRR 7 disabled, there will be a free MTRR available for X
to use.
Dave