linux-kernel - Re: [RFC 09/10] misc: hisi_hikey

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Message-ID: <20200904124523.GE4625@sirena.org.uk>
Date:   Fri, 4 Sep 2020 13:45:23 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        John Stultz <john.stultz@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 09/10] misc: hisi_hikey_usb: add support for Hikey 970

On Fri, Sep 04, 2020 at 02:38:48PM +0200, Mauro Carvalho Chehab wrote:
> Em Fri, 4 Sep 2020 13:23:03 +0100
> Mark Brown <broonie@...nel.org> escreveu:
> 
> > On Fri, Sep 04, 2020 at 12:23:31PM +0200, Mauro Carvalho Chehab wrote:
> > 
> > > +	regulator = devm_regulator_get_optional(&pdev->dev, "hub-vdd");
> > > +	if (IS_ERR(regulator)) {
> > > +		if (PTR_ERR(regulator) == -EPROBE_DEFER) {
> > > +			dev_info(&pdev->dev,
> > > +				 "waiting for hub-vdd-supply to be probed\n");
> > > +			return PTR_ERR(regulator);
> > > +		}
> > > +
> > > +		/* let it fall back to regulator dummy */
> > > +		regulator = devm_regulator_get(&pdev->dev, "hub-vdd");
> > > +		if (IS_ERR(regulator)) {
> > > +			dev_err(&pdev->dev,
> > > +				"get hub-vdd-supply failed with error %ld\n",
> > > +				PTR_ERR(regulator));
> > > +			return PTR_ERR(regulator);
> > > +		}
> > > +	}  

> > This seems weird - if the supply is non-optional why is the code trying
> > with devm_regulator_get_optional()?  Just use normal get directly.

> That's meant to avoid problems with EPROBE_DEFER.

Which problems and in what way does it avoid them?

> See, Hikey 970 need to initialize 4 drivers for the regulators:
> SPMI core, SPMI bus controller, MFD and regulator. This can take
> some time. So, a first call to *regulator_get() may return
> EPROBE_DEFER, specially if both regulator drivers and USB HUB
> are builtin.

This is totally normal and works fine with normal regulator_get().

> I ended doing the same as some other DRM drivers do (like adv7535).

I can't find any references to regulator_get_optional()
drivers/gpu/drm/bridge/adv7511/adv7511_drv.c?

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