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Date:   Mon, 8 Nov 2021 18:28:41 -0800
From:   Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-pm@vger.kernel.org, x86@kernel.org,
        linux-doc@vger.kernel.org, Len Brown <len.brown@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Amit Kucheria <amitk@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ricardo Neri <ricardo.neri@intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/7] thermal: intel: hfi: Minimally initialize the
 Hardware Feedback Interface
Message-ID: <20211109022841.GB16930@ranerica-svr.sc.intel.com>
References: <20211106013312.26698-1-ricardo.neri-calderon@linux.intel.com>
 <20211106013312.26698-4-ricardo.neri-calderon@linux.intel.com>
 <YYjkOkFmDG9IMPHu@hirez.programming.kicks-ass.net>
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On Mon, Nov 08, 2021 at 09:47:54AM +0100, Peter Zijlstra wrote:
> On Fri, Nov 05, 2021 at 06:33:08PM -0700, Ricardo Neri wrote:
> > +static __init int hfi_parse_features(void)
> > +{
> > +	unsigned int nr_capabilities, reg;
> > +
> 
> > +	/*
> > +	 * If we are here we know that CPUID_HFI_LEAF exists. Parse the
> > +	 * supported capabilities and the size of the HFI table.
> > +	 */
> > +	reg = cpuid_edx(CPUID_HFI_LEAF);
> > +
> > +	hfi_features.capabilities = reg & HFI_CAPABILITIES_MASK;
> > +	if (!(hfi_features.capabilities & HFI_CAPABILITIES_PERFORMANCE)) {
> > +		pr_err("Performance reporting not supported! Not using HFI\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	/* The number of 4KB pages required by the table */
> > +	hfi_features.nr_table_pages = ((reg & CPUID_HFI_TABLE_SIZE_MASK) >>
> > +				      CPUID_HFI_TABLE_SIZE_SHIFT) + 1;
> > +
> 
> > +/* Hardware Feedback Interface Enumeration */
> > +#define CPUID_HFI_LEAF			6
> > +#define CPUID_HFI_CAP_MASK		0xff
> > +#define CPUID_HFI_TABLE_SIZE_MASK	0x0f00
> > +#define CPUID_HFI_TABLE_SIZE_SHIFT	8
> > +#define CPUID_HFI_CPU_INDEX_MASK	0xffff0000
> 
> Also, *if* you're going to do something like this, then at least write
> out the masks in full so you can easily see how they relate. The above
> is crap.
> 
> > +#define CPUID_HFI_CPU_INDEX_SHIFT	16
> > +
> > +/* Hardware Feedback Interface Pointer */
> > +#define HFI_PTR_VALID_BIT		BIT(0)
> > +#define HFI_PTR_ADDR_SHIFT		12
> > +
> > +/* Hardware Feedback Interface Configuration */
> > +#define HFI_CONFIG_ENABLE_BIT		BIT(0)
> > +
> > +/* Hardware Feedback Interface Capabilities */
> > +#define HFI_CAPABILITIES_MASK		0xff
> > +#define HFI_CAPABILITIES_NR		8
> > +#define HFI_CAPABILITIES_PERFORMANCE	BIT(0)
> > +#define HFI_CAPABILITIES_ENERGY_EFF	BIT(1)
> 
> 
> So personally I prefer a bitfield union a-la cpuid10_eax, cpuid10_ebx
> cpuid10_edx etc.. Barring that, the above can also be written more
> concise using FIELD_GET() from bitfields.
> 
> union cpuid6_edx {
> 	struct {
> 		unsigned int capabilities :  8;
> 		unsigned int table_size   :  4;
> 		unsigned int __reserved   :  4;
> 		unsigned int cpu_index    : 16;
> 	};
> 	unsigned int full;
> };

Sure Peter. This looks more readable. I'll implement it like this.

Thanks and BR,
Ricardo