linux-kernel - Re: [PATCH V2 1/5] perf/x86/intel/uncore: Parse uncore discovery tables

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Message-ID: <d45ac9ca-2b65-3cff-989a-99db5a6096bb@linux.intel.com>
Date:   Tue, 2 Aug 2022 13:23:03 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Lucas De Marchi <lucas.demarchi@...el.com>
Cc:     peterz@...radead.org, 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, tilak.tangudu@...el.com
Subject: Re: [PATCH V2 1/5] perf/x86/intel/uncore: Parse uncore discovery
 tables



On 2022-08-02 12:02 p.m., Lucas De Marchi wrote:
>>> 2) Trying to read the MMIOs when device is possibly in D3 state:
>>
>> The uncore driver skips the device which doesn't support the discovery
>> mechanism.
>> If 1) is fixed, the uncore driver will not touch the MMIO space of a PVC
>> device. The power issue should be gone.
>>
>> I've already sent you a patch to ignore the PVC added OOBMSM device, you
>> can double check with the patch.
> 
> (2) is a more generic issue that I'm mentioning. Forget for a moment we
> are talking about PVC - that will be fixed by (1). We are trying to read
> the mmio from a device that can be in D3, either because it started in
> D3 or because a driver, loaded before intel_uncore, moved it to that
> state. That won't work even if the device supports the discovery
> mechanism.

The uncore driver is designed to only support the *PMON* discovery
table, not all the discovery tables. The DEVSEC_ID 1 indicates the
*PMON* discovery table.

For other devices which support the discovery mechanism, they should use
another DEVSEC_ID. The uncore driver will ignore the device.

Thanks,
Kan