linux-kernel - Re: [PATCH v7 1/1] powerpc/pseries: Interface to represent PAPR firmware attributes

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Date:   Fri, 23 Jul 2021 10:16:32 -0300
From:   Fabiano Rosas <farosas@...ux.ibm.com>
To:     "Pratik R. Sampat" <psampat@...ux.ibm.com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org, kjain@...ux.ibm.com,
        linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org,
        linux-kernel@...r.kernel.org, psampat@...ux.ibm.com,
        pratik.r.sampat@...il.com
Subject: Re: [PATCH v7 1/1] powerpc/pseries: Interface to represent PAPR
 firmware attributes

"Pratik R. Sampat" <psampat@...ux.ibm.com> writes:

> Adds a generic interface to represent the energy and frequency related
> PAPR attributes on the system using the new H_CALL
> "H_GET_ENERGY_SCALE_INFO".
>
> H_GET_EM_PARMS H_CALL was previously responsible for exporting this
> information in the lparcfg, however the H_GET_EM_PARMS H_CALL
> will be deprecated P10 onwards.
>
> The H_GET_ENERGY_SCALE_INFO H_CALL is of the following call format:
> hcall(
>   uint64 H_GET_ENERGY_SCALE_INFO,  // Get energy scale info
>   uint64 flags,           // Per the flag request
>   uint64 firstAttributeId,// The attribute id
>   uint64 bufferAddress,   // Guest physical address of the output buffer
>   uint64 bufferSize       // The size in bytes of the output buffer
> );
>
> This H_CALL can query either all the attributes at once with
> firstAttributeId = 0, flags = 0 as well as query only one attribute
> at a time with firstAttributeId = id, flags = 1.
>
> The output buffer consists of the following
> 1. number of attributes              - 8 bytes
> 2. array offset to the data location - 8 bytes
> 3. version info                      - 1 byte
> 4. A data array of size num attributes, which contains the following:
>   a. attribute ID              - 8 bytes
>   b. attribute value in number - 8 bytes
>   c. attribute name in string  - 64 bytes
>   d. attribute value in string - 64 bytes
>
> The new H_CALL exports information in direct string value format, hence
> a new interface has been introduced in
> /sys/firmware/papr/energy_scale_info to export this information to
> userspace in an extensible pass-through format.
>
> The H_CALL returns the name, numeric value and string value (if exists)
>
> The format of exposing the sysfs information is as follows:
> /sys/firmware/papr/energy_scale_info/
>    |-- <id>/
>      |-- desc
>      |-- value
>      |-- value_desc (if exists)
>    |-- <id>/
>      |-- desc
>      |-- value
>      |-- value_desc (if exists)
> ...
>
> The energy information that is exported is useful for userspace tools
> such as powerpc-utils. Currently these tools infer the
> "power_mode_data" value in the lparcfg, which in turn is obtained from
> the to be deprecated H_GET_EM_PARMS H_CALL.
> On future platforms, such userspace utilities will have to look at the
> data returned from the new H_CALL being populated in this new sysfs
> interface and report this information directly without the need of
> interpretation.
>
> Signed-off-by: Pratik R. Sampat <psampat@...ux.ibm.com>
> Reviewed-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>

Reviewed-by: Fabiano Rosas <farosas@...ux.ibm.com>