Re: [PATCH hwmon-next v1 1/1] hwmon: (mlxreg-fan) Fix macros for tacho fault reading

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Nov 20, 2018 at 02:46:05PM +0000, Vadim Pasternak wrote:
> 
> 
> > -----Original Message-----
> > From: Guenter Roeck <groeck7@gmail.com> On Behalf Of Guenter Roeck
> > Sent: Monday, November 19, 2018 6:15 PM
> > To: Vadim Pasternak <vadimp@mellanox.com>
> > Cc: linux-hwmon@vger.kernel.org; Michael Shych <michaelsh@mellanox.com>
> > Subject: Re: [PATCH hwmon-next v1 1/1] hwmon: (mlxreg-fan) Fix macros for
> > tacho fault reading
> > 
> > On Mon, Nov 19, 2018 at 06:07:40AM +0000, Vadim Pasternak wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Guenter Roeck <groeck7@gmail.com> On Behalf Of Guenter Roeck
> > > > Sent: Friday, November 16, 2018 6:15 PM
> > > > To: Vadim Pasternak <vadimp@mellanox.com>
> > > > Cc: linux-hwmon@vger.kernel.org; Michael Shych
> > > > <michaelsh@mellanox.com>
> > > > Subject: Re: [PATCH hwmon-next v1 1/1] hwmon: (mlxreg-fan) Fix
> > > > macros for tacho fault reading
> > > >
> > > > On Fri, Nov 16, 2018 at 01:47:11PM +0000, Vadim Pasternak wrote:
> > > > > Fix macros for tacometer fault reading.
> > > > > This fix is relevant for three Mellanox systems MQMB7, MSN37,
> > > > > MSN34, which are about to be released to the customers.
> > > > > At the moment, none of them is at customers sites.
> > > > >
> > > > > Fixes: 65afb4c8e7e4 ("hwmon: (mlxreg-fan) Add support for Mellanox
> > > > > FAN
> > > > > driver")
> > > > > Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
> > > > > ---
> > > > >  drivers/hwmon/mlxreg-fan.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/hwmon/mlxreg-fan.c
> > > > > b/drivers/hwmon/mlxreg-fan.c index de46577..d8fa4be 100644
> > > > > --- a/drivers/hwmon/mlxreg-fan.c
> > > > > +++ b/drivers/hwmon/mlxreg-fan.c
> > > > > @@ -51,7 +51,7 @@
> > > > >   */
> > > > >  #define MLXREG_FAN_GET_RPM(rval, d, s)
> > > > 	(DIV_ROUND_CLOSEST(15000000 * 100, \
> > > > >  					 ((rval) + (s)) * (d)))
> > > > > -#define MLXREG_FAN_GET_FAULT(val, mask) (!!((val) ^ (mask)))
> > > > > +#define MLXREG_FAN_GET_FAULT(val, mask) (!((val) ^ (mask)))
> > > >
> > > > You might want to check if the "^" is correct here. It looks fishy,
> > > > since the expression only evaluates to true if a no bit of val
> > > > outside mask is set. I would have expected "&".
> > > >
> > > > Guenter
> > >
> > > Hi Guenter,
> > >
> > > Thanks for you your comment.
> > >
> > > I'll follow your suggestion and change a macros to"
> > > #define MLXREG_FAN_GET_FAULT(val, mask) (!((val & mask) ^ (mask)))
> > >
> > That seems excessively complicated. Why the xor after the & ?
> 
> I wanted to evaluate MLXREG_FAN_GET_FAULT to true in case HW
> reports the fault.
> For 8 bits addressing device in case of fault val is 0xff and mask is set to 0xff.
> For 16 bits - val will be 0xffff and mask will be set to 0xffff.
> 
> So, just simply this macros will work for me:
> #define MLXREG_FAN_GET_FAULT(val, mask) ((val) == (mask))
> or in order to be on the safe side:
> #define MLXREG_FAN_GET_FAULT(val, mask) ((val & mask) == (mask))
> 
That would be much easier to understand.

Thanks,
Guenter

> > 
> > Guenter
> > 
> > > >
> > > > >  #define MLXREG_FAN_PWM_DUTY2STATE(duty)
> > > > 	(DIV_ROUND_CLOSEST((duty) *	\
> > > > >  					 MLXREG_FAN_MAX_STATE,
> > > > 	\
> > > > >  					 MLXREG_FAN_MAX_DUTY))