Re: [PATCH igt] module_reload: remove snd_hda_intel

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 23 Oct 2013, Paulo Zanoni <przanoni@gmail.com> wrote:
> 2013/10/23 Ben Widawsky <ben@bwidawsk.net>:
>> On Mon, Oct 21, 2013 at 11:56:09AM -0200, Paulo Zanoni wrote:
>>> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
>>>
>>> The audio driver uses the power well provided by our driver, so on
>>> Haswell we can't "rmmod i915" if we don't "rmmod snd_hda_intel" first.
>>>
>>> The problem with removing snd_hda_intel is that we also need to kill
>>> its users. On the specific machine I tested, the only user seem to be
>>> alsactl, but on other machines this may change. IMHO we should leave
>>> the "kill user space" step to whoever is running the script, but
>>> Daniel asked me to put it here so we have a better chance of Just
>>> Working on QA's machines.
>>>
>>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
>>> ---
>>>  tests/module_reload | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/tests/module_reload b/tests/module_reload
>>> index 3d8cb85..c1fd395 100755
>>> --- a/tests/module_reload
>>> +++ b/tests/module_reload
>>> @@ -18,6 +18,10 @@ if ! echo 0 > /sys/class/vtconsole/vtcon1/bind ; then
>>>       exit 77
>>>  fi
>>>
>>> +# The sound driver uses our power well
>>> +pkill alsactl
>>> +rmmod snd_hda_intel &> /dev/null
>>> +
>>>  #ignore errors in ips - gen5 only
>>>  rmmod intel_ips &> /dev/null
>>>  rmmod i915
>>> @@ -38,6 +42,8 @@ fi
>>>  modprobe i915
>>>  echo 1 > /sys/class/vtconsole/vtcon1/bind
>>>
>>> +modprobe snd_hda_intel
>>> +
>>>  # try to run something
>>>  $SOURCE_DIR/gem_exec_nop > /dev/null && echo "module successfully loaded again"
>>>
>>
>> I don't really pretend to understand how module dependencies are
>> calculated. However, I would think the dependency should be *somewhere*
>> and so modprobe -r i915 should work.
>
> It's the opposite: "modprobe -r i915" will remove drm.ko,
> drm_kms_helper, i2c-algo-bit and video, but won't remove snd_hda_intel
> (and if you don't remove it first, it will complain that i915.ko is
> still in use).
>
>>
>> Don't read that as a nak. Rather, a wtf is with the existing stuff?
>
> I think the dependency is magically tracked by depmod when it sees the
> Audio driver uses a symbol exported by i915.ko. But a "modinfo
> snd_hda_intel" doesn't show i915.ko on the "depends" section, which is
> strange. I'm also not an expert on this area...

This is because snd_hda_intel does not depend on i915, to make it
possible to use snd_hda_intel without i915. Which makes sense. Instead,
it uses symbol_request() to be able to call a couple of i915 functions
when available.

I don't know if there's a way to check this runtime dependency from
userspace. But obviously you can't remove i915 while snd_hda_intel holds
function pointers to i915. (In fact, intel_ips is the same.)

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center