linux-kernel - [PATCH v2 3/3] phy: core: Update the runtime PM section in the docs to reflect changes

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Date:   Wed, 20 Dec 2017 15:09:20 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Kishon Vijay Abraham I <kishon@...com>,
        linux-kernel@...r.kernel.org
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-renesas-soc@...r.kernel.org,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: [PATCH v2 3/3] phy: core: Update the runtime PM section in the docs to reflect changes

Let's update and clarify he phy documentation, to reflect the latest
changes around the runtime PM deployment in the phy core.

Cc: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---
 Documentation/phy.txt | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/Documentation/phy.txt b/Documentation/phy.txt
index 457c3e0..1c2c761 100644
--- a/Documentation/phy.txt
+++ b/Documentation/phy.txt
@@ -160,19 +160,22 @@ associated with this PHY.
 PM Runtime
 ==========
 
-This subsystem is pm runtime enabled. So while creating the PHY,
-pm_runtime_enable of the phy device created by this subsystem is called and
-while destroying the PHY, pm_runtime_disable is called. Note that the phy
-device created by this subsystem will be a child of the device that calls
-phy_create (PHY provider device).
-
-So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
-pm_runtime_get_sync of PHY provider device because of parent-child relationship.
-It should also be noted that phy_power_on and phy_power_off performs
-phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
-There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
-phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
-phy_pm_runtime_forbid for performing PM operations.
+This subsystem deploys runtime PM support. More precisely, calls to
+pm_runtime_get_sync() and to pm_runtime_put() surrounds calls to the phy
+provider callbacks, ->init|exit(), in phy_init|exit(). At phy_power_on(), the
+runtime PM usage count is raised again, via pm_runtime_get_sync(). The usage
+count remain raised, until the internal phy power on count reaches zero in
+phy_power_off(), at which point pm_runtime_put() is called to restore the
+runtime PM usage count. In this way, the device is guranteed to stay runtime
+resumed as long as the phy is powered on.
+
+In regards to the runtime PM deployment in the phy core, it should also be
+noted that it's deployed for the phy provider device, which is the parent of
+the phy child device. In other words, the phy device created by the phy core
+remains runtime PM disabled. Of course, whether runtime PM is really used or
+not, depends on whether the phy provider driver has enabled runtime PM for its
+provider device. More exactly, pm_runtime_enable() needs to be called prior
+calling phy_create() or devm_phy_create().
 
 PHY Mappings
 ============
-- 
2.7.4