linux-kernel - Re: [PATCH] platform/x86/amd/hsmp: mark hsmp_msg_desc_table[] as maybe

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Message-ID: <046687d8-1e2d-435b-adcb-26897bfd29f7@redhat.com>
Date: Wed, 30 Oct 2024 18:17:02 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Arnd Bergmann <arnd@...db.de>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Arnd Bergmann <arnd@...nel.org>, Suma Hegde <suma.hegde@....com>
Cc: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, Carlos Bilbao <carlos.bilbao.osdev@...il.com>,
 "H. Peter Anvin" <hpa@...or.com>, Randy Dunlap <rdunlap@...radead.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, platform-driver-x86@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] platform/x86/amd/hsmp: mark hsmp_msg_desc_table[] as
 maybe_unused

Hi,

On 30-Oct-24 3:19 PM, Arnd Bergmann wrote:
> On Wed, Oct 30, 2024, at 14:16, Hans de Goede wrote:
>> On 29-Oct-24 1:55 PM, Ilpo Järvinen wrote:
>>> On Mon, 28 Oct 2024, Arnd Bergmann wrote:
>>>
>>> It seems that the main goal why it was put into UAPI was "to give the user 
>>> some reference about proper num_args and response_size for each message":
>>>
>>> https://lore.kernel.org/all/CAPhsuW5V0BJT+YSwv1U=hRG0k9zBWXeRd=E1n4U5hvcnwEV3mQ@mail.gmail.com/
>>>
>>> Are we actually expecting userspace to benefit from this in C form?
>>> Suma? Hans?
>>
>> I can see how having this available in the uapi header as documentation
>> of sorts is somewhat useful.
>>
>> OTOH I do agree that this array should probably not be used by userspace.
>>
>> And there is only 1 way to find out if it is actually used (which I do not
>> expect) and that is to just drop it and find out (and to be willing to
>> revert the change if it breaks things).
>>
>> So we can either move the array in its entirety to the c-code consuming it,
>> which I think would be best; or we can go with Arnd's patch + add
>>
>> #ifdef __KERNEL__ 
>>
>> around the array so that it is there for people reading the header, but
>> it is no longer exposed as uapi.
>>
> 
> I don't think that would work, because the 'make headers_install'
> step just removes the contents of #ifdef __KERNEL__, in this case
> you just end up with a uapi header that doesn't have the array.

Ah I did not realize that.

Ok so lets just move the definition to the .c file which actually
uses the array and then add a comment like this:

/*
 * See hsmp_msg_desc_table[] in:
 * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/platform/x86/amd/hsmp.c
 * 
 * for some information on number of input- and output arguments
 * for the various functions.
 *
 * Please find the supported list of messages and message definition
 * in the HSMP chapter of respective family/model PPR.
 */

Note please replace hsmp.c with the .c file to which the array
is actually moving ...

Regards,

Hans