linux-kernel - Re: [PATCH 3/3] mfd: arizona: Use regmap_read_poll

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Date:   Thu, 5 Jan 2017 10:05:28 +0000
From:   Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:     Lee Jones <lee.jones@...aro.org>
CC:     <patches@...nsource.wolfsonmicro.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mfd: arizona: Use regmap_read_poll_timeout instead
 of hard coding it

On Thu, Jan 05, 2017 at 08:07:01AM +0000, Lee Jones wrote:
> On Wed, 04 Jan 2017, Charles Keepax wrote:
> 
> > arizona_poll_reg essentially hard-codes regmap_read_poll_timeout, this
> > patch updates the implementation to use regmap_read_poll_timeout. We
> > still keep arizona_poll_reg around as regmap_read_poll_timeout is a
> > macro so rather than expand this for each caller keep it wrapped in
> > arizona_poll_reg.
> > 
> > Signed-off-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
> > ---
> >  drivers/mfd/arizona-core.c | 28 +++++++++++-----------------
> >  1 file changed, 11 insertions(+), 17 deletions(-)
> > 
> > diff --git a/drivers/mfd/arizona-core.c b/drivers/mfd/arizona-core.c
> > index 4cb34c3..e6fae3c 100644
> > --- a/drivers/mfd/arizona-core.c
> > +++ b/drivers/mfd/arizona-core.c
> > @@ -236,28 +236,22 @@ static irqreturn_t arizona_overclocked(int irq, void *data)
> >  }
> >  
> >  static int arizona_poll_reg(struct arizona *arizona,
> > -			    int timeout, unsigned int reg,
> > +			    int npolls, unsigned int reg,
> >  			    unsigned int mask, unsigned int target)
> >  {
> > +	const int poll_us = 7500;
> 
> Get rid of this and replace its usage with a nice #define describing
> exactly what the timeout is for i.e what timed out.
> 

I can replace this with a define if you prefer although since the
value is only used locally I generally prefer a const variable as
it keeps all the relevant code together.

> ... okay, I just read the doc.  This should really be 'SLEEP'.
> 
> Where did 7500 come from anyway?  Is it documented?
> 

To be fair this number is a little pulled from my ... err the
air. But basically provides a reasonable balance of timing
between polls for the various users of the function. It didn't
really seem worth having each user specify its own timing for
this part as we generally don't care down to a couple of mS here
or there.

> >  	unsigned int val = 0;
> > -	int ret, i;
> > -
> > -	for (i = 0; i < timeout; i++) {
> > -		ret = regmap_read(arizona->regmap, reg, &val);
> > -		if (ret != 0) {
> > -			dev_err(arizona->dev, "Failed to read reg 0x%x: %d\n",
> > -				reg, ret);
> > -			continue;
> > -		}
> > -
> > -		if ((val & mask) == target)
> > -			return 0;
> > +	int ret;
> >  
> > -		usleep_range(1000, 5000);
> > -	}
> > +	ret = regmap_read_poll_timeout(arizona->regmap,
> > +				       ARIZONA_INTERRUPT_RAW_STATUS_5, val,
> > +				       ((val & mask) == target), poll_us,
> > +				       npolls * poll_us);
> 
> What's the relevance of npolls?  Is this number documented, or was it
> pulled from your ... err, the air?
> 

Its an argument passed into the function, its called npolls in a
function that polls a register I really don't know how to make
the fact it is the number of polls to do any more clear than
that. As for the number passed into the function that depends on
how long that particular register should be polled for, this is a
function that is used in several places for polling for a
particular register state.

Would all these issues perhaps be best solved by my adding some
kernel doc for the function with some more description of what
everything is?

Thanks,
Charles

> > +	if (ret)
> > +		dev_err(arizona->dev, "Polling reg 0x%x timed out: %x\n",
> > +			reg, val);
> >  
> > -	dev_err(arizona->dev, "Polling reg 0x%x timed out: %x\n", reg, val);
> > -	return -ETIMEDOUT;
> > +	return ret;
> >  }
> >  
> >  static int arizona_wait_for_boot(struct arizona *arizona)
> 
> -- 
> Lee Jones
> Linaro STMicroelectronics Landing Team Lead
> Linaro.org │ Open source software for ARM SoCs
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