linux-kernel - Re: [PATCH 1/3] x86/amd_nb: Add support for HSMP mailbox access

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Message-ID: <ad2bbcad-857c-f39d-9bee-49cd8ad582b2@amd.com>
Date:   Wed, 8 Sep 2021 22:41:20 +0530
From:   "Chatradhi, Naveen Krishna" <nchatrad@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux@...ck-us.net, yazen.ghannam@....com,
        mingo@...hat.com, nathan.fontenot@....com, lewis.carroll@....com,
        Ingo Molnar <mingo@...nel.org>,
        Jean Delvare <jdelvare@...e.com>
Subject: Re: [PATCH 1/3] x86/amd_nb: Add support for HSMP mailbox access

HI Boris,

On 9/2/2021 11:28 PM, Borislav Petkov wrote:
> [CAUTION: External Email]
>
> On Thu, Sep 02, 2021 at 11:11:53PM +0530, Naveen Krishna Chatradhi wrote:
>> On Fam19h server CPUs from AMD an HSMP (Host System Management Port)
>> mailbox interface is added to monitor and manage the CPU parameters.
> Mailbox? Hmm, that rings a bell. There's drivers/mailbox/ with a bunch
> of drivers in there. Those are
>
> "Mailbox is a framework to control hardware communication between
> on-chip processors through queued messages and interrupt driven
> signals."
>
> I wonder if that HSMP thing can be wrapped like a mailbox driver...

Sure, I will look into the mailbox framework.

>
> If not, I still don't like it being slapped in amd_nb.c where it would
> be built in on *all* AMD hardware which is kinda too much.

In all the future server platforms, AMD's direction is the support HSMP 
interface, which exposes system management knobs.

>
> You could make it a separate driver module called amd_hsmp.ko which
> loads only on the appropriate hw and uses amd_nb.c for detection only
> like the other drivers, for example.

How about, creating a module under drivers/platform/x86/ (lets say 
amd_hsmp.c) export an API from here and it can be extended to support 
all the knobs that does not fit in an existing frameworks (such as 
hwmon, etc) and provide a user space access.

I can see similar references in the drivers/platform/x86/ directory.

>
> --
> Regards/Gruss,
>      Boris.
>
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