linux-kernel - Re: [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables

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Message-ID: <YFCZyqz+56bB8n2k@hirez.programming.kicks-ass.net>
Date:   Tue, 16 Mar 2021 12:43:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     mingo@...nel.org, acme@...hat.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        eranian@...gle.com, namhyung@...nel.org, ak@...ux.intel.com
Subject: Re: [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables

On Fri, Mar 12, 2021 at 08:34:34AM -0800, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> A self-describing mechanism for the uncore PerfMon hardware has been
> introduced with the latest Intel platforms. By reading through an MMIO
> page worth of information, perf can 'discover' all the standard uncore
> PerfMon registers in a machine.
> 
> The discovery mechanism relies on BIOS's support. With a proper BIOS,
> a PCI device with the unique capability ID 0x23 can be found on each
> die. Perf can retrieve the information of all available uncore PerfMons
> from the device via MMIO. The information is composed of one global
> discovery table and several unit discovery tables.

> If a BIOS doesn't support the 'discovery' mechanism, there is nothing
> changed.

What if the BIOS got it wrong? Will the driver still get it correct if
it is a known platform?

Do we need a chicken flag to kill the discovery? uncore_no_discover?