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

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Date:   Sat, 4 Nov 2017 19:22:34 +0100 (CET)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>, Ray Jui <rjui@...adcom.com>,
        Eric Anholt <eric@...olt.net>,
        Rob Herring <robh+dt@...nel.org>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        Harald Freudenberger <freude@...ux.vnet.ibm.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        Scott Branden <sbranden@...adcom.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>, Martin Kaiser <martin@...ser.cx>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
        "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." 
        <bcm-kernel-feedback-list@...adcom.com>,
        Mark Rutland <mark.rutland@....com>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Sean Wang <sean.wang@...iatek.com>
Subject: Re: [PATCH 07/12] hwrng: bcm2835-rng: Manage an optional clock

> Florian Fainelli <f.fainelli@...il.com> hat am 4. November 2017 um 18:59 geschrieben:
> 
> 
> Hi Stefan,
> 
> On 11/04/2017 06:50 AM, Stefan Wahren wrote:
> > Hi Florian,
> > 
> >> Florian Fainelli <f.fainelli@...il.com> hat am 2. November 2017 um 02:04 geschrieben:
> >>
> >>
> >> One of the last steps before bcm63xx-rng can be eliminated is to manage
> >> a clock during hwrng::init and hwrng::cleanup, so fetch it in the probe
> >> function, and manage it during these two steps when valid.
> >>
> >> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> >> ---
> >>  drivers/char/hw_random/bcm2835-rng.c | 14 ++++++++++++++
> >>  1 file changed, 14 insertions(+)
> >>
> >> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
> >> index ed20e0b6b7ae..35928efb52e7 100644
> >> --- a/drivers/char/hw_random/bcm2835-rng.c
> >> +++ b/drivers/char/hw_random/bcm2835-rng.c
> >> @@ -15,6 +15,7 @@
> >>  #include <linux/of_platform.h>
> >>  #include <linux/platform_device.h>
> >>  #include <linux/printk.h>
> >> +#include <linux/clk.h>
> >>  
> >>  #define RNG_CTRL	0x0
> >>  #define RNG_STATUS	0x4
> >> @@ -33,6 +34,7 @@ struct bcm2835_rng_priv {
> >>  	struct hwrng rng;
> >>  	void __iomem *base;
> >>  	bool mask_interrupts;
> >> +	struct clk *clk;
> >>  };
> >>  
> >>  static inline struct bcm2835_rng_priv *to_rng_priv(struct hwrng *rng)
> >> @@ -67,6 +69,11 @@ static int bcm2835_rng_init(struct hwrng *rng)
> >>  {
> >>  	struct bcm2835_rng_priv *priv = to_rng_priv(rng);
> >>  	u32 val;
> >> +	int ret;
> >> +
> >> +	ret = clk_prepare_enable(priv->clk);
> >> +	if (ret)
> >> +		return ret;
> >>  
> >>  	if (priv->mask_interrupts) {
> >>  		/* mask the interrupt */
> >> @@ -88,6 +95,8 @@ static void bcm2835_rng_cleanup(struct hwrng *rng)
> >>  
> >>  	/* disable rng hardware */
> >>  	__raw_writel(0, priv->base + RNG_CTRL);
> >> +
> >> +	clk_disable_unprepare(priv->clk);
> >>  }
> >>  
> >>  struct bcm2835_rng_of_data {
> >> @@ -130,6 +139,11 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
> >>  		return PTR_ERR(priv->base);
> >>  	}
> >>  
> >> +	/* 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.

http://elixir.free-electrons.com/linux/latest/source/drivers/usb/dwc2/platform.c#L247

> 
> -- 
> Florian
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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