linux-kernel - [PATCH] firmware: imx: scu-pd: Update comments for single global power domain

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Date:   Wed, 17 Mar 2021 10:31:17 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Shawn Guo <shawnguo@...nel.org>,
        Dong Aisheng <aisheng.dong@....com>,
        Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Liu Ying <victor.liu@....com>, Peng Fan <peng.fan@....com>,
        NXP Linux Team <linux-imx@....com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] firmware: imx: scu-pd: Update comments for single global power domain

Since the introduction of the PM domain support for the scu-pd, the genpd
framework has been continuously improved. More preciously, using a single
global power domain can quite easily be deployed for imx platforms.

To avoid confusions, let's therefore make an update to the comments about
the missing pieces.

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---
 drivers/firmware/imx/scu-pd.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/imx/scu-pd.c b/drivers/firmware/imx/scu-pd.c
index 08533ee67626..6e178a63442d 100644
--- a/drivers/firmware/imx/scu-pd.c
+++ b/drivers/firmware/imx/scu-pd.c
@@ -29,6 +29,10 @@
  *    The framework needs some proper extension to support multi power
  *    domain cases.
  *
+ *    Update: Genpd assigns the ->of_node for the virtual device before it
+ *    invokes ->attach_dev() callback, hence parsing for device resources via
+ *    DT should work fine.
+ *
  * 2. It also breaks most of current drivers as the driver probe sequence
  *    behavior changed if removing ->power_on|off() callback and use
  *    ->start() and ->stop() instead. genpd_dev_pm_attach will only power
@@ -39,8 +43,11 @@
  *    domain enabled will trigger a HW access error. That means we need fix
  *    most drivers probe sequence with proper runtime pm.
  *
- * In summary, we need fix above two issue before being able to switch to
- * the "single global power domain" way.
+ *    Update: Runtime PM support isn't necessary. Instead, this can easily be
+ *    fixed in drivers by adding a call to dev_pm_domain_start() during probe.
+ *
+ * In summary, the second part needs to be addressed via minor updates to the
+ * relevant drivers, before the "single global power domain" model can be used.
  *
  */
 
-- 
2.25.1