[EdLUG] Module parameters are different from cmdline

[Edinburgh Linux Users Group]

Maxim,

A few respones inlined.

On 2016.12.28 19:49, Edinburgh Linux Users Group wrote:
> Hi Roy,
> 
> Thanks for the detailed response!
> 
> I don't seem to have /proc/confg.gz, however I think I was able to
> find it
> in /boot:
> 
> 
> *$ grep 915 /boot/config-4.8.0-32-generic
> CONFIG_CHARGER_DA9150=m
> CONFIG_BATTERY_DA9150=m
> CONFIG_MFD_DA9150=m
> CONFIG_DRM_I915=m#
> CONFIG_DRM_I915_PRELIMINARY_HW_SUPPORT is not set
> CONFIG_DRM_I915_USERPTR=y
> CONFIG_DRM_I915_GVT=y
> # drm/i915 Debugging#
> CONFIG_DRM_I915_WERROR is not set
> # CONFIG_DRM_I915_DEBUG is not set
> CONFIG_SND_HDA_I915=yCONFIG_DA9150_GPADC=m*
> 
> CONFIG_DRM_I915 is set to 'm', so I presume it was compiled as a
> module

That's correct.
> 
> Yeah, I found in Google that some settings can be changed at runtime,
> without module reload, but unfortunately this particular option is
> read-only in /sys :(
> 
> I think you're right - this particular one should be in initramfs and
> is
> most likely loaded even before the root fs is mounted. However, I
> thought
> that it should still pick up the parameters from the Kernel command
> line.
You can see root being mounted in dmesg.  I get

[    4.499945] EXT4-fs (dm-10): couldn't mount as ext3 due to feature incompatibilities
[    4.500337] EXT4-fs (dm-10): couldn't mount as ext2 due to feature incompatibilities
[    4.522369] EXT4-fs (dm-10): mounted filesystem with ordered data mode. Opts: (null)

and later

[   11.019172] EXT4-fs (dm-10): re-mounted. Opts: discard

Anything that loads before 4.522369 seconds in my example, must 
either be built into the kernel, or come from the initramfs.  That 
mount is the real root being mounted read only, so it can be checked.   

The remount at 11.019172 sec is root being mounted read/write.

You should be able to find similar entries in your dmesg then
work out where i915 comes from.  As its =m, its either the 
initramfs if its before root is mounted read only or your real root,
if its after root being mounted.

> 
> I've just noticed some weird entries in the dmesg output. It seems
> like
> it's i915 module specific, but I'm still trying to google anything
> that can
> indicate what they're supposed to mean:
> 
> [    1.480619] Setting dangerous option enable_rc6 - tainting kernel
> [    1.480621] Setting dangerous option enable_psr - tainting kernel
> [    1.480622] Setting dangerous option enable_fbc - tainting kernel
> [    1.480624] i915: unknown parameter 'lvds_downclock' ignored
> [    1.480626] Setting dangerous option semaphores - tainting kernel
> 

Setting dangerous option ..., is advice from the i915 module itself.

Tainting kernel means that some debugging options are disabled
and that support for kernel problems from kernel developers will
start with "Can you reproduce that with an untainted kernel?"


> 
> *[    1.480628] Setting dangerous option enable_execlists - tainting
> kernel[    1.480631] Setting dangerous option enable_execlists -
> tainting
> kernel*
> 
> Best Regards,
> Maxim
> 
[snip]

Regards,

Roy Bamford