linux-kernel - [PATCH 02/10] PM / devfreq: Do not require devices to have OPPs

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Message-Id: <20210929044254.38301-3-samuel@sholland.org>
Date:   Tue, 28 Sep 2021 23:42:46 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Samuel Holland <samuel@...lland.org>
Subject: [PATCH 02/10] PM / devfreq: Do not require devices to have OPPs

Since commit ea572f816032 ("PM / devfreq: Change return type of
devfreq_set_freq_table()"), all devfreq devices are required to have a
valid freq_table. If freq_table is not provided by the driver, it will
be filled in by set_freq_table() from the OPPs; if that fails,
devfreq_add_device() will return an error.

However, since commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when
adding the devfreq device"), devfreq devices are _also_ required to have
an OPP table, even if they provide freq_table. devfreq_add_device()
requires dev_pm_opp_find_freq_ceil() and dev_pm_opp_find_freq_floor() to
return successfully, specifically to initialize scaling_min/max_freq.

Not all drivers need an OPP table. For example, a driver where all
frequencies are determined dynamically could work by filling out only
freq_table. But with the current code it must call dev_pm_opp_add() on
every freq_table entry to probe successfully.

The offending properties, scaling_min/max_freq, are only necessary if a
device has OPPs; if no OPPs exist at all, OPPs cannot be dynamically
enabled or disabled, so those values have no effect. Thus it is trivial
to restore support for devices with freq_table only and not OPPs -- move
those initializations behind the check for a valid OPP table.

Since get_freq_range() uses scaling_max_freq in a min() expression, it
must be initialized to the maximum possible value. scaling_min_freq is
initialized as well for consistency.

Fixes: ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when adding the devfreq device")
Signed-off-by: Samuel Holland <samuel@...lland.org>
---
 drivers/devfreq/devfreq.c | 36 ++++++++++++++++++++----------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 7a8b022ba456..426e31e6c448 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -835,24 +835,28 @@ struct devfreq *devfreq_add_device(struct device *dev,
 		mutex_lock(&devfreq->lock);
 	}

-	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
-	if (!devfreq->scaling_min_freq) {
-		mutex_unlock(&devfreq->lock);
-		err = -EINVAL;
-		goto err_dev;
-	}
-
-	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
-	if (!devfreq->scaling_max_freq) {
-		mutex_unlock(&devfreq->lock);
-		err = -EINVAL;
-		goto err_dev;
-	}
-
-	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
 	devfreq->opp_table = dev_pm_opp_get_opp_table(dev);
-	if (IS_ERR(devfreq->opp_table))
+	if (IS_ERR(devfreq->opp_table)) {
 		devfreq->opp_table = NULL;
+		devfreq->scaling_min_freq = 0;
+		devfreq->scaling_max_freq = ULONG_MAX;
+	} else {
+		devfreq->scaling_min_freq = find_available_min_freq(devfreq);
+		if (!devfreq->scaling_min_freq) {
+			mutex_unlock(&devfreq->lock);
+			err = -EINVAL;
+			goto err_dev;
+		}
+
+		devfreq->scaling_max_freq = find_available_max_freq(devfreq);
+		if (!devfreq->scaling_max_freq) {
+			mutex_unlock(&devfreq->lock);
+			err = -EINVAL;
+			goto err_dev;
+		}
+
+		devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
+	}

 	atomic_set(&devfreq->suspend_count, 0);

-- 
2.31.1