Re: [gentoo-user] Re: Another X11 problem

[Corbin Bird]

On 08/25/2016 09:59 PM, Ian Zimmerman wrote:
> On 2016-08-25, Corbin Bird wrote:
>
>> On 08/25/2016 12:52 PM, Ian Zimmerman wrote:
>>> On 2016-08-22, Adam Carter wrote:
>>>
>>>>> Once or twice per week, when I start X11 (via the startx program),
>>>>> my display goes all black.  When it happens there is no way back to
>>>>> a working state: I can see that Xorg is running, I can exit it by
>>>>> hitting Ctl-Alt-Backspace, but even then display does not recover.
>>>>> The only thing I can do is hit Ctl-Alt-Del blindly and reboot, and
>>>>> next time it usually works.
>>>> Have you checked dmesg and syslogs for messages?
>>> Yes.  Nothing (significantly) different when this happens.
>>>
>>>> Try a newer kernel and see if it goes away.
>>> I'm reluctant to go there before nailing it down a bit more, since
>>> it only happens intermittently and a newer kernel will quite possibly
>>> introduce other problems.
>>>
>> I don't remember if you specified your appended command-line kernel
>> parameters ( lilo / grub / grub2 ). I have an AMD Phenom II x4 980. The
>> parameters have a major effect on the video ( i.e. AGP / IOMMU usage ).
>>
>>
> I have not posted them yet because I didn't suspect they were
> important, but here they are now:
>
> GRUB_CMDLINE_LINUX="rootfstype=ext4"
>
> GRUB_CMDLINE_LINUX_DEFAULT="quiet noresume vt.default_utf8=1 consoleblank=0"
>
> # Uncomment to disable graphical terminal (grub-pc only)
> GRUB_TERMINAL=console
>
>
> I added the consoleblank=0 bit just very recently in the pursuit of this
> bug.  It happened without it, too.
>
> The relevant kernel drivers are built as modules.  I load fbcon from
> /etc/conf.d/modules, and that seems to be where the switch to graphics
> mode occurs.  Note that everything is always okay at this point -
> it just switches to a framebuffer enabled console, with a nice small
> font.  The bug, if it happens, happens later, when I start xorg.
>
> Also, I pass no module-specific parameters.  The only non-comment line
> in /etc/conf.d/modules is:
>
> modules="fbcon it87"
>
Try setting up the IOMMU. ( Stabilize memory setup / management )

The IOMMU is really a modified "AGP bridge" built into the CPU.

Typical dmesg output :
[    0.000000] AGP: No AGP bridge found

If you don't create a "reserved for the AGP Aperature" memory block or 
setup the IOMMU, the kernel will setup 64Mg of memory and reserve it for 
"e820 -> AGP Aperature". If the IOMMU is not setup, it will 
automatically use ALL of the "AGP Aperature Reserved" memory.

The added kernel parameter for ( AGP / IOMMU on x86_64 ) : 
iommu=memaper[=1],noaperture

This sets up 64Mg for the IOMMU, and tells it "do not touch 'reserved 
for the AGP Aperature' memory".
( Software IO TLB is now preferred / automatic on 4.1.xx kernels. )

Typical dmesg output :
[    0.636904] AMD-Vi: Found IOMMU at 0000:00:00.2 cap 0x40
[    0.637060] AMD-Vi: Interrupt remapping enabled
[    0.644282] AMD-Vi: Lazy IO/TLB flushing enabled
[    0.717543] PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
[    0.717700] software IO TLB [mem 0xb9ee4000-0xbdee4000] (64MB) mapped 
at [ffff8800b9ee4000-ffff8800bdee3fff]

KMS enabled X drivers need this setup on ( Fam10h / Fam15h ) CPUs.

Also check for any kernel parameters needed for KMS, by your choice of 
video driver.

Hope this helps.

Corbin