linux-kernel - Re: [PATCH 1/3] ACPI: PCC: Add PCC shared memory region command and status bitfields

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Date:   Wed, 27 Sep 2023 14:59:09 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     "lihuisong (C)" <lihuisong@...wei.com>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-acpi@...r.kernel.org,
        Sudeep Holla <sudeep.holla@....com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH 1/3] ACPI: PCC: Add PCC shared memory region command and
 status bitfields

On Wed, Sep 27, 2023 at 10:07:15AM +0800, lihuisong (C) wrote:
> Hi Sudeep,
> 
> 在 2023/9/26 20:28, Sudeep Holla 写道:
> > Define the common macros to use when referring to various bitfields in
> > the PCC generic communications channel command and status fields.
>
> Can you define the bit0 macros in the "flags" for Extended PCC Subspace
> Shared Memory Region?

Sure I will take a look and include it in v2 if applicable.

> > 
> > Currently different drivers that need to use these bitfields have defined
> > these locally. This common macro is intended to consolidate and replace
> > those.
> > 
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> > ---
> >   include/acpi/pcc.h | 11 +++++++++++
> >   1 file changed, 11 insertions(+)
> > 
> > diff --git a/include/acpi/pcc.h b/include/acpi/pcc.h
> > index 73e806fe7ce7..66d9934c2ee4 100644
> > --- a/include/acpi/pcc.h
> > +++ b/include/acpi/pcc.h
> > @@ -18,7 +18,18 @@ struct pcc_mbox_chan {
> >   	u16 min_turnaround_time;
> >   };
> > +/* Generic Communications Channel Shared Memory Region */
> > +#define PCC_SIGNATURE			0x50424300
> Why is this signature 0x50424300?

It is as per the specification.

> In ACPI spec, this signature is all 0x50434303.

No, not exactly. It is just an example.
The PCC signature - The signature of a subspace is computed by a bitwise-or
of the value 0x50434300 with the subspace ID. For example, subspace 3 has
signature 0x50434303

And I see the driver you mentioned(drivers/soc/hisilicon/kunpeng_hccs.c)
is doing the right thing. I am bit confused as why you being the author
of the driver are now confused.

-- 
Regards,
Sudeep