[Bug 108085] Intel GeminiLake corruption at top of screen caused by fbc

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108085

--- Comment #40 from James Ausmus <james.ausmus at intel.com> ---
Hi Geraud-

If


$ cat /sys/module/i915/parameters/enable_fbc


gives you a 1, that means that the module parameter is set to allow FBC.
However, this doesn't necessarily mean that FBC is active/enabled.

To check this, you'll need to either look at a file in debugfs, or boot with
the "drm.debug=0xe" parameter and check your kernel logs.

To check the file in debugfs, do:


$ mount | grep debugfs


if this doesn't return results, then debugfs isn't mounted (or may not even be
enabled in your kernel config) - you can choose to enable/mount debugfs if you
choose - see https://www.kernel.org/doc/Documentation/filesystems/debugfs.txt
for some examples.

If the mount command *did* return results, it probably looked something like:


$ mount | grep debugfs
debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)


Then you can do:


$ cat /sys/kernel/debug/dri/0/i915_fbc_status


which will give you the "this moment right now" status of FBC.

Alternatively, if you wan't to check via the kernel log, boot with the
"drm.debug=0xe" kernel parameter, and then do:


$ dmesg | grep -i fbc


Which should give at least a few lines about FBC enabling and FBC status.

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