linux-kernel - Re: [PATCH 07/12] hwrng: bcm2835-rng: Manage an optional clock

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Date:   Sat, 4 Nov 2017 20:37:31 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Sean Wang <sean.wang@...iatek.com>,
        Martin Kaiser <martin@...ser.cx>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>, Matt Mackall <mpm@...enic.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>,
        Harald Freudenberger <freude@...ux.vnet.ibm.com>,
        Rob Herring <robh+dt@...nel.org>,
        "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." 
        <bcm-kernel-feedback-list@...adcom.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>
Subject: Re: [PATCH 07/12] hwrng: bcm2835-rng: Manage an optional clock

Hi Florian

> > >> +	/* Clock is optional on most platforms */
> > >> +	priv->clk = devm_clk_get(dev, NULL);
> > >> +	if (IS_ERR(priv->clk))
> > >> +		priv->clk = NULL;
> > > 
> > > at least in case of EPROBE_DEFERED this isn't the expected behavior. Maybe we should better trigger on non-existing clock?
> > 
> > Good point, so more like:
> > 
> > if (IS_ERR(priv->clk) && PTR_ERR(priv->clk) == -ENODEV)?
> 

> Unfortunately we need to return the error in all other cases. Please
> take a look at devm_usb_get_phy in dwc2 [1]. AFAIK we don't need to
> take care of ENXIO in our case.

A few subsystems have a get_optional() call, e.g.
devm_phy_optional_get(). It does not return an error when the phy is
not supposed to exist, but in all other cases, it does.

Maybe consider adding devm_clk_get_optional()?

      Andrew