linux-kernel - Re: [PATCH v2 0/9] sound: Use -EPROBE_DEFER instead of i915 module loading.

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Date:   Tue, 1 Aug 2023 09:27:47 +0200
From:   Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     alsa-devel@...a-project.org, sound-open-firmware@...a-project.org,
        linux-kernel@...r.kernel.org, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Daniel Baluta <daniel.baluta@....com>
Subject: Re: [PATCH v2 0/9] sound: Use -EPROBE_DEFER instead of i915 module
 loading.

Hey,

Den 2023-07-31 kl. 21:32, skrev Takashi Iwai:
> On Mon, 31 Jul 2023 18:37:36 +0200,
> Maarten Lankhorst wrote:
>> Hey,
>>
>> Den 2023-07-31 kl. 17:51, skrev Takashi Iwai:
>>> On Wed, 19 Jul 2023 18:41:32 +0200,
>>> Maarten Lankhorst wrote:
>>>> Explicitly loading i915 becomes a problem when upstreaming the new intel driver
>>>> for Tiger Lake and higher graphics (xe). By loading i915, it doesn't wait for
>>>> driver load of xe, and will fail completely before it loads.
>>>>
>>>> -EPROBE_DEFER has to be returned before any device is created in probe(),
>>>> otherwise the removal of the device will cause EPROBE_DEFER to try again
>>>> in an infinite loop.
>>>>
>>>> The conversion is done in gradual steps. First I add an argument to
>>>> snd_hdac_i915_init to allow for -EPROBE_DEFER so I can convert each driver
>>>> separately. Then I convert each driver to move snd_hdac_i915_init out of the
>>>> workqueue. Finally I drop the ability to choose modprobe behavior after the
>>>> last user is converted.
>>>>
>>>> I suspect the avs and skylake drivers used snd_hdac_i915_init purely for the
>>>> modprobe, but I don't have the hardware to test if it can be safely removed.
>>>> It can still be done easily in a followup patch to simplify probing.
>>>>
>>>> ---
>>>> New since first version:
>>>>
>>>> - snd_hda_core.gpu_bind is added as a mechanism to force gpu binding,
>>>>     for testing. snd_hda_core.gpu_bind=0 forces waiting for GPU bind to
>>>>     off, snd_hda_core.gpu_bind=1 forces waiting for gpu bind. Default
>>>>     setting depends on whether kernel booted with nomodeset.
>>>> - Incorporated all feedback review.
>>> Maarten, are you working on v3 patch set?
>>> Or, for moving forward, should we merge v2 now and fix the rest based
>>> on that later?
>> I've been working on a small change to keep the workqueue in SOF and
>> only move the binding to the probe function to match what
>> snd-hda-intel is doing, but I don't know if that is needed?
>>
>> It was a bit unclear to me based on feedback if I should try to kill
>> the workqueue on all drivers (but with no way to test), or keep it
>> around.
> I guess it's still safer to keep the workqueue in many drivers.  There
> can be modprobe or firmware loading at any later stage.
> We can get rid of the workqueue once after confirming that it's really
> safe, too.
>
> So, if you can work on the patch set in that regard, it's fine, I can
> wait for it.

I've finished that patch, but it caused regressions (oops) while 
rebooting. I think it's safer to kill the workqueue for SOC, and then 
convert all other drivers later.

Cheers,

~Maarten