linux-kernel - Re: [PATCH v4 3/6] ACPI: CPPC: Add macros to generally implement registers getting and setting functions

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Message-ID: <CAJZ5v0jmZy0tNO7Btc9-A0rfzL5jPp2ZEH99bEX00cEi3z+XcQ@mail.gmail.com>
Date: Wed, 15 Jan 2025 12:12:57 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, lenb@...nel.org, robert.moore@...el.com, 
	viresh.kumar@...aro.org, mario.limonciello@....com, gautham.shenoy@....com, 
	ray.huang@....com, pierre.gondois@....com, acpica-devel@...ts.linux.dev, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, linuxarm@...wei.com, jonathan.cameron@...wei.com, 
	zhanjie9@...ilicon.com, lihuisong@...wei.com, hepeng68@...wei.com, 
	fanghao11@...wei.com
Subject: Re: [PATCH v4 3/6] ACPI: CPPC: Add macros to generally implement
 registers getting and setting functions

On Wed, Jan 15, 2025 at 9:59 AM zhenglifeng (A) <zhenglifeng1@...wei.com> wrote:
>
> On 2025/1/15 1:58, Rafael J. Wysocki wrote:
>
> > On Mon, Jan 13, 2025 at 1:21 PM Lifeng Zheng <zhenglifeng1@...wei.com> wrote:
> >>
> >> Add CPPC_REG_VAL_READ() to implement registers getting functions.
> >>
> >> Add CPPC_REG_VAL_WRITE() to implement registers setting functions.
> >>
> >> Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
> >
> > I don't particularly like these macros as they will generally make it
> > harder to follow the code.
> >
> >> ---
> >>  drivers/acpi/cppc_acpi.c | 14 ++++++++++++++
> >>  1 file changed, 14 insertions(+)
> >>
> >> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> >> index 571f94855dce..6326a1536cda 100644
> >> --- a/drivers/acpi/cppc_acpi.c
> >> +++ b/drivers/acpi/cppc_acpi.c
> >> @@ -1279,6 +1279,20 @@ static int cppc_set_reg_val(int cpu, enum cppc_regs reg_idx, u64 val)
> >>         return cpc_write(cpu, reg, val);
> >>  }
> >>
> >> +#define CPPC_REG_VAL_READ(reg_name, reg_idx)           \
> >> +int cppc_get_##reg_name(int cpu, u64 *val)             \
> >> +{                                                      \
> >> +       return cppc_get_reg_val(cpu, reg_idx, val);     \
> >> +}                                                      \
> >> +EXPORT_SYMBOL_GPL(cppc_get_##reg_name)
> >
> > What about if defining something like
> >
> > #define CPPC_READ_REG_VAL(cpu, reg_name, val)
> > cppc_get_reg_val((cpu), CPPC_REG_IDX(reg_name), (val))
> >
> > (and analogously for the WRITE_ part), where CPPC_REG_IDX(reg_name) is
> >
> > #define CPPC_REG_IDX(reg_name)    CPPC_REG_##reg_name_IDX
> >
> > and there are CPPC_REG_##reg_name_IDX macros defined for all register
> > names in use?
> >
> > For example
> >
> > #define CPPC_REG_desired_perf_IDX   DESIRED_PERF
>
> What about keeping these two macros but replace reg_idx with
> CPPC_REG_IDX(reg_name)? With this, the only needed parameter for these two
> macros is reg_name.

The problem is that looking up functions defined through macros is
hard when somebody wants to know what they do, so I'd prefer to avoid
doing that.