linux-kernel - Re: [PATCH v2] mfd: arizona: Don't use regmap_read_poll

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Message-ID: <20180618062754.GF31141@dell>
Date:   Mon, 18 Jun 2018 07:27:54 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     andy.shevchenko@...il.com, patches@...nsource.cirrus.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mfd: arizona: Don't use regmap_read_poll_timeout

On Mon, 04 Jun 2018, Charles Keepax wrote:

> Some Arizona CODECs have a small timing window where they will
> NAK an I2C transaction if it happens before the boot done bit is
> set. This can cause the read of the register containing the boot
> done bit to fail until it is set. Since regmap_read_poll_timeout
> will abort polling if a read fails it can't be reliably used to
> poll the boot done bit over I2C.
> 
> Do a partial revert of ef84f885e037 ("mfd: arizona: Refactor
> arizona_poll_reg"), removing the regmap_read_poll_timeout but
> leaving the refactoring to make the arizona_poll_reg take more
> sensible arguments.
> 
> Fixes: ef84f885e037 ("mfd: arizona: Refactor arizona_poll_reg")
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> ---
> 
> Changes since v1:
>  - Explicitly include ktime header
>  - Use USEC_PER_MSEC instead of a constant
>  - Refactor the loop to not use a while (true)
> 
> Thanks,
> Charles
> 
>  drivers/mfd/arizona-core.c | 29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mfd/arizona-core.c b/drivers/mfd/arizona-core.c
> index 83f1c5a516d99..fe0c151d9d9d7 100644
> --- a/drivers/mfd/arizona-core.c
> +++ b/drivers/mfd/arizona-core.c
> @@ -24,6 +24,7 @@
>  #include <linux/regulator/consumer.h>
>  #include <linux/regulator/machine.h>
>  #include <linux/slab.h>
> +#include <linux/ktime.h>
>  #include <linux/platform_device.h>
>  
>  #include <linux/mfd/arizona/core.h>
> @@ -240,18 +241,28 @@ static int arizona_poll_reg(struct arizona *arizona,
>  			    int timeout_ms, unsigned int reg,
>  			    unsigned int mask, unsigned int target)
>  {
> +	ktime_t timeout = ktime_add_us(ktime_get(), timeout_ms * USEC_PER_MSEC);
>  	unsigned int val = 0;
> -	int ret;
> +	int ret = regmap_read(arizona->regmap, reg, &val);

I'm not a fan of this type of initialisation.

Also, what's the point of assigning 'ret' if you never check it?

> -	ret = regmap_read_poll_timeout(arizona->regmap,
> -				       reg, val, ((val & mask) == target),
> -				       ARIZONA_REG_POLL_DELAY_US,
> -				       timeout_ms * 1000);
> -	if (ret)
> -		dev_err(arizona->dev, "Polling reg 0x%x timed out: %x\n",
> -			reg, val);
> +	while (ktime_compare(ktime_get(), timeout) <= 0) {
> +		if ((val & mask) == target)
> +			return 0;
>  
> -	return ret;
> +		usleep_range(ARIZONA_REG_POLL_DELAY_US / 2,
> +			     ARIZONA_REG_POLL_DELAY_US);
> +
> +		ret = regmap_read(arizona->regmap, reg, &val);
> +	}
> +
> +	if (ret) {
> +		dev_err(arizona->dev, "Failed polling reg 0x%x: %d\n",
> +			reg, ret);
> +		return ret;
> +	}
> +
> +	dev_err(arizona->dev, "Polling reg 0x%x timed out: %x\n", reg, val);
> +	return -ETIMEDOUT;
>  }
>  
>  static int arizona_wait_for_boot(struct arizona *arizona)

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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