linux-kernel - Re: [patch 17/29] x86/cpu: Provide a sane leaf 0xb/0x1f parser

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Date:   Tue, 25 Jul 2023 08:51:12 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        James Smart <james.smart@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-hwmon@...r.kernel.org,
        Jean Delvare <jdelvare@...e.com>,
        Huang Rui <ray.huang@....com>,
        Guenter Roeck <linux@...ck-us.net>,
        Steve Wahl <steve.wahl@....com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>
Subject: Re: [patch 17/29] x86/cpu: Provide a sane leaf 0xb/0x1f parser

On Mon, Jul 24 2023 at 22:49, Peter Zijlstra wrote:
> On Mon, Jul 24, 2023 at 07:44:17PM +0200, Thomas Gleixner wrote:
>
>> +static inline bool topo_subleaf(struct topo_scan *tscan, u32 leaf, u32 subleaf)
>> +{
>> +	unsigned int dom, maxtype = leaf == 0xb ? CORE_TYPE + 1 : MAX_TYPE;
>> +	struct {
>> +		// eax
>> +		u32	x2apic_shift	:  5, // Number of bits to shift APIC ID right
>> +					      // for the topology ID at the next level
>> +			__rsvd0		: 27; // Reserved
>> +					      // ebx
>> +		u32	num_processors	: 16, // Number of processors at current level
>> +			__rsvd1		: 16; // Reserved
>> +					      // ecx
>> +		u32	level		:  8, // Current topology level. Same as sub leaf number
>> +			type		:  8, // Level type. If 0, invalid
>> +			__rsvd2		: 16; // Reserved
>> +					      // edx
>> +		u32	x2apic_id	: 32; // X2APIC ID of the current logical processor
>
> That comment seems inconsistent, either have then all aligned or move
> all register names left.

Bah. I had all the register names left at some point. No idea how I lost
that again. Probably when I rolled back to some earlier version after
screwing up :)

>> +
>> +	/* Read all available subleafs and populate the levels */
>> +	for (subleaf = 0; topo_subleaf(tscan, leaf, subleaf); subleaf++);
>
> Personally I prefer:
>
> 	for (;;)
> 		;
>
> that is, have the semicolon on it's own line, but meh.

:)