Re: [PATCH v4 1/5] counter: Internalize sysfs interface code

[David Lechner]

> > > > >     
> > > > >     CPMAC ETHERNET DRIVER
> > > > >     M:	Florian Fainelli <f.fainelli@xxxxxxxxx>
> > > > > diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> > > > > index 78766b6ec271..0f20920073d6 100644
> > > > > --- a/drivers/counter/104-quad-8.c
> > > > > +++ b/drivers/counter/104-quad-8.c
> > > > > @@ -621,7 +621,7 @@ static const struct iio_chan_spec quad8_channels[] = {
> > > > >     };
> > > > >     
> > > > >     static int quad8_signal_read(struct counter_device *counter,
> > > > > -	struct counter_signal *signal, enum counter_signal_value *val)
> > > > > +			     struct counter_signal *signal, u8 *val)
> > > >
> > > > I'm not a fan of replacing enum types with u8 everywhere in this patch.
> > > > But if we have to for technical reasons (e.g. causes compiler error if
> > > > we don't) then it would be helpful to add comments giving the enum type
> > > > everywhere like this instance where u8 is actually an enum value.
> > > >
> > > > If we use u32 as the generic type for enums instead of u8, I think the
> > > > compiler will happlily let us use enum type and u32 interchangeably and
> > > > not complain.
> > >
> > > I switched to fixed-width types after the suggestion by David Laight:
> > > https://lkml.org/lkml/2020/5/3/159. I'll CC David Laight just in case he
> > > wants to chime in again.
> > >
> > > Enum types would be nice for making the valid values explicit, but there
> > > is one benefit I have appreciated from the move to fixed-width types:
> > > there has been a significant reduction of duplicate code; before, we had
> > > a different read function for each different enum type, but now we use a
> > > single function to handle them all.
> >
> > Yes, what I was trying to explain is that by using u32 instead of u8, I
> > think we can actually do both.
> >
> > The function pointers in struct counter_device *counter would use u32 as a
> > generic enum value in the declaration, but then the actual implementations
> > could still use the proper enum type.
>
> Oh, I see what you mean now. So for example:
>
>      int (*signal_read)(struct counter_device *counter,
>                         struct counter_signal *signal, u8 *val)
>
> This will become instead:
>
>      int (*signal_read)(struct counter_device *counter,
>                         struct counter_signal *signal, u32 *val)
>
> Then in the driver callback implementation we use the enum type we need:
>
>      enum counter_signal_level signal_level = COUNTER_SIGNAL_HIGH;
>      ...
>      *val = signal_level;
>
> Is that what you have in mind?

Yes.

Additionally, if we have...


      int (*x_write)(struct counter_device *counter,
                     ..., u32 val)
 
We should be able to define the implementation as:

static int my_driver_x_write(struct counter_device *counter,
                             ..., enum some_type val)
{
	...
}

Not sure if it works if val is a pointer though. Little-
endian systems would probably be fine, but maybe not big-
endian combined with -fshort-enums compiler flag.


      int (*x_read)(struct counter_device *counter,
                    ..., u32 *val)
 

static int my_driver_x_read(struct counter_device *counter,
                            ..., enum some_type *val)
{
	...
}