linux-kernel - Re: [RFC PATCH 1/2] driver core: export driver_deferred_probe

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Date:   Wed, 18 Aug 2021 10:53:07 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
        "Rafael J . Wysocki" <rafael@...nel.org>, tiwai@...e.de,
        linux-kernel@...r.kernel.org, liam.r.girdwood@...ux.intel.com,
        vkoul@...nel.org, Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH 1/2] driver core: export
 driver_deferred_probe_trigger()




>> a) we have to use request_module()
> 
> Wait, why?
> 
> module loading is async, use auto-loading when the hardware/device is
> found and reported to userspace.  Forcing a module to load by the kernel
> is not always wise as the module is not always present in the filesystem
> at that point in time at boot (think modules on the filesystem, not in
> the initramfs).
> 
> Try fixing this issue and maybe it will resolve itself as you should be
> working async.

It's been that way for a very long time (2015?) for HDAudio support, see
sound/pci/hda/hda_bind.c. It's my understanding that it was a conscious
design decision to use vendor-specific modules, if available, and
fallback to generic modules if the first pass failed.

Takashi, you may want to chime in...