linux-kernel - Re: [PATCH 1/3] regulator: twl: Make sure we have access to powerbus before trying to write to it

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Date:	Sun, 24 Apr 2016 18:10:02 +0200
From:	Pavel Machek <pavel@....cz>
To:	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Cc:	tony@...mide.com, lgirdwood@...il.com, broonie@...nel.org,
	sre@...nel.org, pali.rohar@...il.com, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] regulator: twl: Make sure we have access to powerbus
 before trying to write to it

Hi!

> According to the TRM, we need to enable i2c access to powerbus before
> writing to it. Also, a new write to powerbus should not be attempted if
> there is a pending transfer. The current code does not implement that
> functionality and while there are no known problems caused by that, it is
> better to follow what TRM says.
> 
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> ---
>  drivers/regulator/twl-regulator.c | 78 +++++++++++++++++++++++++++++++++++----
>  1 file changed, 70 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/regulator/twl-regulator.c b/drivers/regulator/twl-regulator.c
> index 955a6fb..aad748b0 100644
> --- a/drivers/regulator/twl-regulator.c
> +++ b/drivers/regulator/twl-regulator.c
> @@ -21,7 +21,7 @@
>  #include <linux/regulator/machine.h>
>  #include <linux/regulator/of_regulator.h>
>  #include <linux/i2c/twl.h>
> -
> +#include <linux/delay.h>
>  
>  /*
>   * The TWL4030/TW5030/TPS659x0/TWL6030 family chips include power management, a
> @@ -188,6 +188,74 @@ static int twl6030reg_is_enabled(struct regulator_dev *rdev)
>  	return grp && (val == TWL6030_CFG_STATE_ON);
>  }
>  
> +#define PB_I2C_BUSY	BIT(0)
> +#define PB_I2C_BWEN	BIT(1)
> +
> +/* Wait until buffer empty/ready to send a word on power bus. */
> +static int twl4030_wait_pb_ready(void)
> +{
> +
> +	int	ret;
> +	int	timeout = 10;
> +	u8	val;
> +

Can we do this plain

    while (timeout--) {
    }...

? Also... if the bit is not immediately available, it will wait for
1msec. Would it make sense to have timeout = 1000 but wait only 10usec
each time or something?

Thanks,
								Pavel
								
> +	do {
> +		ret = twl_i2c_read_u8(TWL_MODULE_PM_MASTER, &val,
> +				      TWL4030_PM_MASTER_PB_CFG);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (!(val & PB_I2C_BUSY))
> +			return 0;
> +
> +		mdelay(1);
> +		timeout--;
> +	} while (timeout);
> +
> +	return -ETIMEDOUT;
> +}

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html