From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: David Lechner <david@lechnology.com>
Cc: kamel.bouhara@bootlin.com, gwendal@chromium.org,
alexandre.torgue@st.com, linux-iio@vger.kernel.org,
patrick.havelange@essensium.com, alexandre.belloni@bootlin.com,
linux-kernel@vger.kernel.org, David.Laight@ACULAB.COM,
linux-arm-kernel@lists.infradead.org, mcoquelin.stm32@gmail.com,
fabrice.gasnier@st.com, syednwaris@gmail.com,
linux-stm32@st-md-mailman.stormreply.com, jic23@kernel.org
Subject: Re: [PATCH v4 1/5] counter: Internalize sysfs interface code
Date: Sat, 15 Aug 2020 12:33:11 -0400 [thread overview]
Message-ID: <20200815163255.GA6974@shinobu> (raw)
In-Reply-To: <ca6337f5-b28b-a19e-735c-3cd124570c27@lechnology.com>
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On Mon, Aug 10, 2020 at 05:48:07PM -0500, David Lechner wrote:
>
> >>>>>
> >>>>> CPMAC ETHERNET DRIVER
> >>>>> M: Florian Fainelli <f.fainelli@gmail.com>
> >>>>> 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)
> {
> ...
> }
Regardless of endianness for pointers, will targets that have
-fshort-enums enabled by default present a problem here? I imagine that
in these cases enum some_type will have a size of unsigned char because
that is the first type that can represent all the values:
https://gcc.gnu.org/onlinedocs/gcc/Structures-unions-enumerations-and-bit-fields-implementation.html
What I'm worried about is whether we can gurantee u32 val can be swapped
out with enum some_type val -- or if this is not possible because some
architectures will be built with -fshort-enums enabled?
William Breathitt Gray
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next prev parent reply other threads:[~2020-08-15 16:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 19:35 [PATCH v4 0/5] Introduce the Counter character device interface William Breathitt Gray
2020-07-21 19:35 ` [PATCH v4 2/5] docs: counter: Update to reflect sysfs internalization William Breathitt Gray
2020-07-21 19:35 ` [PATCH v4 3/5] counter: Add character device interface William Breathitt Gray
2020-07-29 0:20 ` David Lechner
2020-07-30 22:49 ` David Lechner
2020-07-31 8:13 ` Alexandre Belloni
2020-08-02 21:11 ` William Breathitt Gray
2020-08-09 14:51 ` William Breathitt Gray
2020-08-10 23:02 ` David Lechner
2020-08-15 17:23 ` William Breathitt Gray
2020-07-21 19:35 ` [PATCH v4 4/5] docs: counter: Document " William Breathitt Gray
2020-07-21 19:35 ` [PATCH v4 5/5] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2020-07-30 17:07 ` Syed Nayyar Waris
[not found] ` <e13d43849f68af8227c6aaa0ef672b459d47e9ab.1595358237.git.vilhelm.gray@gmail.com>
[not found] ` <7209ac3d-d1ca-1b4c-b22c-8d98b13742e2@lechnology.com>
[not found] ` <20200802210415.GA606173@shinobu>
2020-08-03 20:00 ` [PATCH v4 1/5] counter: Internalize sysfs interface code David Lechner
2020-08-09 13:42 ` Jonathan Cameron
2020-08-09 19:15 ` William Breathitt Gray
2020-08-10 22:48 ` David Lechner
2020-08-15 16:33 ` William Breathitt Gray [this message]
2020-08-09 13:48 ` [PATCH v4 0/5] Introduce the Counter character device interface Jonathan Cameron
2020-08-09 17:51 ` William Breathitt Gray
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