Re: [prefix=PATCH] drivers: pmbus: core: Prevent calling pmbus_set_page with negative page

[Eddie James]

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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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