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

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Message-ID: <20210818182833.GI4177@sirena.org.uk>
Date:   Wed, 18 Aug 2021 19:28:33 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.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()

On Wed, Aug 18, 2021 at 01:09:44PM -0500, Pierre-Louis Bossart wrote:

> I initially looked at the component framework to try to express
> dependencies. It's really not clear to me if this is the 'right'
> direction, for ASoC-based solutions we already have components that
> register with a core.

Historically (long before both deferred probe and the component
framework) ASoC used to implement a mechanism that essentially did
deferred probe for the dependencies - it'd maintain it's own lists of
dependencies and then tell the machine driver and all the components
when the card was ready.  Once deferred probe was there we dropped all
the open coded deferral stuff since it was just reimplementing what
deferred probe does in a slightly more complicated fashion (it tracked
the dependencies in a finer grained manner, though the result wasn't any
different).  See b19e6e7b76 (ASoC: core: Use driver core probe deferral)
for the conversion.

What ASoC is doing with the cards is fundamentally the same thing as
what the component helpers are doing, we could in theory convert to
using that but unlike with probe deferral it doesn't really save us any
work and we'd still need all the card level tracking we've got to
connect the various bits of the card together and order things.  If we
were starting from scratch we would probably use components but there's
far more pressing things to be getting on with otherwise.

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