linux-kernel - Re: [PATCH 3/3] reset: socfpga: add empty driver allowing consumers to probe

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Message-ID: <6993ccdaf8f3f248f4ff1c739445e0f798ee0efa.camel@pengutronix.de>
Date:   Tue, 05 Oct 2021 12:22:25 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Paweł Anikiel <pan@...ihalf.com>,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        robh+dt@...nel.org, arnd@...db.de, olof@...om.net, soc@...nel.org,
        dinguyen@...nel.org
Cc:     linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Tomasz Nowicki <tn@...ihalf.com>,
        Konrad Adamczyk <ka@...ihalf.com>,
        Jacek Majkowski <jam@...ihalf.com>
Subject: Re: [PATCH 3/3] reset: socfpga: add empty driver allowing consumers
 to probe

On Tue, 2021-10-05 at 13:12 +0200, Paweł Anikiel wrote:
> On Tue, Oct 5, 2021 at 11:34 AM Philipp Zabel <p.zabel@...gutronix.de> wrote:
> > Hi Paweł,
> > 
> > On Mon, 2021-09-20 at 14:41 +0200, Paweł Anikiel wrote:
> > > The early reset driver doesn't ever probe, which causes consuming
> > > devices to be unable to probe. Add an empty driver to set this device
> > > as available, allowing consumers to probe.
> > > 
> > > Signed-off-by: Paweł Anikiel <pan@...ihalf.com>
> > > ---
> > >  drivers/reset/reset-socfpga.c | 26 ++++++++++++++++++++++++++
> > >  1 file changed, 26 insertions(+)
> > > 
> > > diff --git a/drivers/reset/reset-socfpga.c b/drivers/reset/reset-socfpga.c
> > > index 2a72f861f798..8c6492e5693c 100644
> > > --- a/drivers/reset/reset-socfpga.c
> > > +++ b/drivers/reset/reset-socfpga.c
> > > @@ -92,3 +92,29 @@ void __init socfpga_reset_init(void)
> > >       for_each_matching_node(np, socfpga_early_reset_dt_ids)
> > >               a10_reset_init(np);
> > >  }
> > > +
> > > +/*
> > > + * The early driver is problematic, because it doesn't register
> > > + * itself as a driver. This causes certain device links to prevent
> > > + * consumer devices from probing. The hacky solution is to register
> > > + * an empty driver, whose only job is to attach itself to the reset
> > > + * manager and call probe.
> > > + */
> > > +static const struct of_device_id socfpga_reset_dt_ids[] = {
> > > +     { .compatible = "altr,rst-mgr", },
> > > +     { /* sentinel */ },
> > > +};
> > > +
> > > +static int reset_simple_probe(struct platform_device *pdev)
> > > +{
> > > +     return 0;
> > > +}
> > > +
> > > +static struct platform_driver reset_socfpga_driver = {
> > > +     .probe  = reset_simple_probe,
> > > +     .driver = {
> > > +             .name           = "socfpga-reset",
> > > +             .of_match_table = socfpga_reset_dt_ids,
> > > +     },
> > > +};
> > > +builtin_platform_driver(reset_socfpga_driver);
> > 
> > If we can just let devlink delay all consumers until the empty driver is
> > probed, does the reset controller have to be registered early at all?
> > 
> > regards
> > Philipp
> 
> I asked Dinh if the reset controller code needs to be called early:
> 
> > That's correct. It's for one of the SP timers.

Ah, right, those call of_reset_control_get() from TIMER_OF_DECLARE().
Thank you, I'll apply this to reset/fixes.

regards
Philipp