linux-kernel - Re: [PATCH v2 0/3] pmdomain: ti_sci: collect and send low-power mode constraints

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Message-ID: <7hplphah5w.fsf@baylibre.com>
Date: Thu, 05 Sep 2024 15:07:23 -0700
From: Kevin Hilman <khilman@...libre.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: linux-pm@...r.kernel.org, Nishanth Menon <nm@...com>, Vibhore Vardhan
 <vibhore@...com>, Dhruva Gole <d-gole@...com>, Akashdeep Kaur
 <a-kaur@...com>, Sebin Francis <sebin.francis@...com>, Markus
 Schneider-Pargmann <msp@...libre.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] pmdomain: ti_sci: collect and send low-power
 mode constraints

Ulf Hansson <ulf.hansson@...aro.org> writes:

> On Tue, 20 Aug 2024 at 02:00, Kevin Hilman <khilman@...libre.com> wrote:
>>
>> The latest (10.x) version of the firmware for the PM co-processor (aka
>> device manager, or DM) adds support for a "managed" mode, where the DM
>> firmware will select the specific low power state which is entered
>> when Linux requests a system-wide suspend.
>>
>> In this mode, the DM will always attempt the deepest low-power state
>> available for the SoC.
>>
>> However, Linux (or OSes running on other cores) may want to constrain
>> the DM for certain use cases.  For example, the deepest state may have
>> a wakeup/resume latency that is too long for certain use cases.  Or,
>> some wakeup-capable devices may potentially be powered off in deep
>> low-power states, but if one of those devices is enabled as a wakeup
>> source, it should not be powered off.
>>
>> These kinds of constraints are are already known in Linux by the use
>> of existing APIs such as per-device PM QoS and device wakeup APIs, but
>> now we need to communicate these constraints to the DM.
>>
>> For TI SoCs with TI SCI support, all DM-managed devices will be
>> connected to a TI SCI PM domain.  So the goal of this series is to use
>> the PM domain driver for TI SCI devices to collect constraints, and
>> communicate them to the DM via the new TI SCI APIs.
>>
>> This is all managed by TI SCI PM domain code.  No new APIs are needed
>> by Linux drivers.  Any device that is managed by TI SCI will be
>> checked for QoS constraints or wakeup capability and the constraints
>> will be collected and sent to the DM.
>>
>> This series depends on the support for the new TI SCI APIs (v10) and
>> was also tested with this series to update 8250_omap serial support
>> for AM62x[2].
>>
>> [1] https://lore.kernel.org/all/20240801195422.2296347-1-msp@baylibre.com
>> [2] https://lore.kernel.org/all/20240807141227.1093006-1-msp@baylibre.com/
>>
>> Signed-off-by: Kevin Hilman <khilman@...libre.com>
>> ---
>> Changes in v2:
>>
>> - To simplify this version a bit, drop the pmdomain ->power_off()
>>   changes.  Constraints only sent during ->suspend() path.  The pmdomain
>>   path was an optimization that may be added back later.
>> - With the above simplification, drop the extra state variables that
>>   had been added to keep track of constraint status.
>> - Link to v1: https://lore.kernel.org/r/20240805-lpm-v6-10-constraints-pmdomain-v1-0-d186b68ded4c@baylibre.com
>>
>> ---
>> Kevin Hilman (3):
>>       pmdomain: ti_sci: add per-device latency constraint management
>>       pmdomain: ti_sci: add wakeup constraint management
>>       pmdomain: ti_sci: handle wake IRQs for IO daisy chain wakeups
>>
>>  drivers/pmdomain/ti/ti_sci_pm_domains.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 76 insertions(+)
>> ---
>> base-commit: ad7eb1b6b92ee0c959a0a6ae846ddadd7a79ea64
>> change-id: 20240802-lpm-v6-10-constraints-pmdomain-f33df5aef449
>>
>> Best regards,
>> --
>> Kevin Hilman <khilman@...libre.com>
>
> Besides a couple of minor things that I have commented on for each
> patch, this looks okay to me!
>
> Taking into account the other series that this depends on, what is the
> best merging strategy? Is it safe for me to take it through my
> pmdomain tree?


That other series should be merged shortly, so I will check with
Nishanth (on cc) if he can create an immutable branch/tag that you could
use in your tree.

It has a build-time dependency on that other series, so I think this is
the best way.

Alternatively, if you don't expect this to clash with other changes in
your tree, with your ack/reviewed-by, Nishanth could merge this series
via his tree and we could avoid the cross-tree shuffle.

Either way will work.  Up to you.

Kevin