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Date:   Wed, 25 Oct 2017 16:23:01 -0500
From:   Eddie James <eajames@...ux.vnet.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
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 10/25/2017 04:12 PM, Guenter Roeck wrote:
> 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 ..."

Yea I hit = instead of - in "--subject-prefix"...

>
> 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 ?

Yea that works well too, and reduces the code size. Though I suppose it 
makes the interface slightly less intuitive, as someone might think they 
can pass a value larger than u8. At least for the read/write functions, 
a negative value has a meaning - "don't change the page."

Up to you, either way. I'm happy to change it.

Thanks,
Eddie

>
> 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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