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From:   Steven Price <steven.price@arm.com>
Subject: Re: [PATCH] drm/panfrost: Fix regulator_get_optional() misuse
To:     Rob Herring <robh@kernel.org>
Cc:     Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        David Airlie <airlied@linux.ie>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Mark Brown <broonie@kernel.org>
References: <20190904123032.23263-1-broonie@kernel.org>
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Date:   Mon, 9 Sep 2019 17:22:55 +0100
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On 09/09/2019 16:41, Rob Herring wrote:
> On Fri, Sep 6, 2019 at 4:23 PM Steven Price <steven.price@arm.com> wrote:
>>
>> On 04/09/2019 13:30, Mark Brown wrote:
>>> The panfrost driver requests a supply using regulator_get_optional()
>>> but both the name of the supply and the usage pattern suggest that it is
>>> being used for the main power for the device and is not at all optional
>>> for the device for function, there is no meaningful handling for absent
>>> supplies.  Such regulators should use the vanilla regulator_get()
>>> interface, it will ensure that even if a supply is not described in the
>>> system integration one will be provided in software.
>>>
>>> Signed-off-by: Mark Brown <broonie@kernel.org>
>>
>> Tested-by: Steven Price <steven.price@arm.com>
>>
>> Looks like my approach to this was wrong - so we should also revert the
>> changes I made previously.
>>
>> ----8<----
>> From fe20f8abcde8444bb41a8f72fb35de943a27ec5c Mon Sep 17 00:00:00 2001
>> From: Steven Price <steven.price@arm.com>
>> Date: Fri, 6 Sep 2019 15:20:53 +0100
>> Subject: [PATCH] drm/panfrost: Revert changes to cope with NULL regulator
>>
>> Handling a NULL return from devm_regulator_get_optional() doesn't seem
>> like the correct way of handling this. Instead revert the changes in
>> favour of switching to using devm_regulator_get() which will return a
>> dummy regulator instead.
>>
>> Reverts commit 52282163dfa6 ("drm/panfrost: Add missing check for pfdev->regulator")
>> Reverts commit e21dd290881b ("drm/panfrost: Enable devfreq to work without regulator")
> 
> Does a straight revert of these 2 patches not work? If it does work,
> can you do that and send to the list. I don't want my hand slapped
> again reverting things.

I wasn't sure what was best here - 52282163dfa6 is a bug fix, so
reverting that followed by e21dd290881b would (re-)introduce a
regression for that one commit (i.e. not completely bisectable).
Reverting in the other order would work, but seems a little odd.
Squashing the reverts seemed the neatest option - but it's not my hand
at risk... :)

Perhaps it would be best to simply apply Mark's change followed by
something like the following. That way it's not actually a revert!
It also avoids (re-)adding the now redundant check in
panfrost_devfreq_init().

Steve

---8<----
From fb2956acdf46ca04095ef11363c136dc94a1ab18 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price@arm.com>
Date: Fri, 6 Sep 2019 15:20:53 +0100
Subject: [PATCH] drm/panfrost: Remove NULL checks for regulator

devm_regulator_get() is now used to populate pfdev->regulator which
ensures that this cannot be NULL (a dummy regulator will be returned if
necessary). So remove the checks in panfrost_devfreq_target().

Signed-off-by: Steven Price <steven.price@arm.com>
---
 drivers/gpu/drm/panfrost/panfrost_devfreq.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
index a1f5fa6a742a..12ff77dacc95 100644
--- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
+++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
@@ -39,7 +39,7 @@ static int panfrost_devfreq_target(struct device *dev, unsigned long *freq,
 	 * If frequency scaling from low to high, adjust voltage first.
 	 * If frequency scaling from high to low, adjust frequency first.
 	 */
-	if (old_clk_rate < target_rate && pfdev->regulator) {
+	if (old_clk_rate < target_rate) {
 		err = regulator_set_voltage(pfdev->regulator, target_volt,
 					    target_volt);
 		if (err) {
@@ -53,14 +53,12 @@ static int panfrost_devfreq_target(struct device *dev, unsigned long *freq,
 	if (err) {
 		dev_err(dev, "Cannot set frequency %lu (%d)\n", target_rate,
 			err);
-		if (pfdev->regulator)
-			regulator_set_voltage(pfdev->regulator,
-					      pfdev->devfreq.cur_volt,
-					      pfdev->devfreq.cur_volt);
+		regulator_set_voltage(pfdev->regulator, pfdev->devfreq.cur_volt,
+				      pfdev->devfreq.cur_volt);
 		return err;
 	}
 
-	if (old_clk_rate > target_rate && pfdev->regulator) {
+	if (old_clk_rate > target_rate) {
 		err = regulator_set_voltage(pfdev->regulator, target_volt,
 					    target_volt);
 		if (err)
-- 
2.20.1