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Date:   Wed, 25 Oct 2017 14:12:34 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eddie James <eajames@...ux.vnet.ibm.com>
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, andrew@...id.au,
        "Edward A. James" <eajames@...ibm.com>
Subject: Re: [prefix=PATCH] drivers: pmbus: core: Prevent calling
 pmbus_set_page with negative page

On Wed, Oct 25, 2017 at 02:52:53PM -0500, Eddie James wrote:
> From: "Edward A. James" <eajames@...ibm.com>
> 
> For devices with word data registers, the pmbus core may call read/write
> word data functions with a page value of -1, in order to perform the
> operation without setting the page. However, the read/write word data
> functions accept only unsigned 8-bit page numbers, resulting in setting
> a page of 0xFF in this situation. This may result in errors or undefined
> behavior of some devices (specifically the ir35221, which allows the
> page to be set to 0xFF, but some subsequent operations to read registers
> may fail).
> 

Good catch.

Subject came off a bit odd. 

[prefix=PATCH] drivers: pmbus: core: Prevent ...

Please use "[PATCH] hwmon: (pmbus/core) Prevent ..."

This me wonder if we should move the check into pmbus_set_page()
instead.

int pmbus_set_page(struct i2c_client *client, int page)
{
	...
	if (page >= 0 && page != data->currpage) {
	...
}

What do you think ?

Thanks,
Guenter

> Signed-off-by: Edward A. James <eajames@...ibm.com>
> ---
>  drivers/hwmon/pmbus/pmbus.h      |  4 ++--
>  drivers/hwmon/pmbus/pmbus_core.c | 29 ++++++++++++++++++-----------
>  2 files changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
> index 4efa2bd..4a16da6 100644
> --- a/drivers/hwmon/pmbus/pmbus.h
> +++ b/drivers/hwmon/pmbus/pmbus.h
> @@ -405,8 +405,8 @@ struct pmbus_driver_info {
>  
>  void pmbus_clear_cache(struct i2c_client *client);
>  int pmbus_set_page(struct i2c_client *client, u8 page);
> -int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg);
> -int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word);
> +int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg);
> +int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg, u16 word);
>  int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg);
>  int pmbus_write_byte(struct i2c_client *client, int page, u8 value);
>  int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg,
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 302f0ae..6d6e030 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -186,13 +186,16 @@ static int _pmbus_write_byte(struct i2c_client *client, int page, u8 value)
>  	return pmbus_write_byte(client, page, value);
>  }
>  
> -int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word)
> +int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg,
> +			  u16 word)
>  {
>  	int rv;
>  
> -	rv = pmbus_set_page(client, page);
> -	if (rv < 0)
> -		return rv;
> +	if (page >= 0) {
> +		rv = pmbus_set_page(client, page);
> +		if (rv < 0)
> +			return rv;
> +	}
>  
>  	return i2c_smbus_write_word_data(client, reg, word);
>  }
> @@ -219,13 +222,15 @@ static int _pmbus_write_word_data(struct i2c_client *client, int page, int reg,
>  	return pmbus_write_word_data(client, page, reg, word);
>  }
>  
> -int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg)
> +int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg)
>  {
>  	int rv;
>  
> -	rv = pmbus_set_page(client, page);
> -	if (rv < 0)
> -		return rv;
> +	if (page >= 0) {
> +		rv = pmbus_set_page(client, page);
> +		if (rv < 0)
> +			return rv;
> +	}
>  
>  	return i2c_smbus_read_word_data(client, reg);
>  }
> @@ -269,9 +274,11 @@ int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg, u8 value)
>  {
>  	int rv;
>  
> -	rv = pmbus_set_page(client, page);
> -	if (rv < 0)
> -		return rv;
> +	if (page >= 0) {
> +		rv = pmbus_set_page(client, page);
> +		if (rv < 0)
> +			return rv;
> +	}
>  
>  	return i2c_smbus_write_byte_data(client, reg, value);
>  }
> -- 
> 1.8.3.1
> 

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