linux-kernel - Re: [PATCH v4 1/4] gpu: drm: meson: Use devm_regulator_*get

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Date:   Wed, 16 Nov 2022 12:02:28 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Matti Vaittinen <mazziesaccount@...il.com>
CC:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Robert Foss <robert.foss@...aro.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-amlogic@...ts.infradead.org" 
        <linux-amlogic@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] gpu: drm: meson: Use devm_regulator_*get_enable*()

Hi dee Ho Laurent & All,

On 10/21/22 18:29, Neil Armstrong wrote:
> Hi,
> 
> On 21/10/2022 17:02, Laurent Pinchart wrote:
>> Hi Matti,
>>
>> On Fri, Oct 21, 2022 at 04:18:01PM +0300, Matti Vaittinen wrote:
>>> Simplify using the devm_regulator_get_enable_optional(). Also drop the
>>> seemingly unused struct member 'hdmi_supply'.
>>>
>>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>>>
>>> ---
>>> v3 => v4:
>>> - split meson part to own patch
>>>
>>> RFCv1 => v2:
>>> - Change also sii902x to use devm_regulator_bulk_get_enable()
>>>
>>> Please note - this is only compile-tested due to the lack of HW. Careful
>>> review and testing is _highly_ appreciated.
>>> ---
>>>   drivers/gpu/drm/meson/meson_dw_hdmi.c | 23 +++--------------------
>>>   1 file changed, 3 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/meson/meson_dw_hdmi.c 
>>> b/drivers/gpu/drm/meson/meson_dw_hdmi.c
>>> index 5cd2b2ebbbd3..7642f740272b 100644
>>> --- a/drivers/gpu/drm/meson/meson_dw_hdmi.c
>>> +++ b/drivers/gpu/drm/meson/meson_dw_hdmi.c
>>> @@ -140,7 +140,6 @@ struct meson_dw_hdmi {
>>>       struct reset_control *hdmitx_apb;
>>>       struct reset_control *hdmitx_ctrl;
>>>       struct reset_control *hdmitx_phy;
>>> -    struct regulator *hdmi_supply;
>>>       u32 irq_stat;
>>>       struct dw_hdmi *hdmi;
>>>       struct drm_bridge *bridge;
>>> @@ -665,11 +664,6 @@ static void meson_dw_hdmi_init(struct 
>>> meson_dw_hdmi *meson_dw_hdmi)
>>>   }
>>> -static void meson_disable_regulator(void *data)
>>> -{
>>> -    regulator_disable(data);
>>> -}
>>> -
>>>   static void meson_disable_clk(void *data)
>>>   {
>>>       clk_disable_unprepare(data);
>>> @@ -723,20 +717,9 @@ static int meson_dw_hdmi_bind(struct device 
>>> *dev, struct device *master,
>>>       meson_dw_hdmi->data = match;
>>>       dw_plat_data = &meson_dw_hdmi->dw_plat_data;
>>> -    meson_dw_hdmi->hdmi_supply = devm_regulator_get_optional(dev, 
>>> "hdmi");
>>> -    if (IS_ERR(meson_dw_hdmi->hdmi_supply)) {
>>> -        if (PTR_ERR(meson_dw_hdmi->hdmi_supply) == -EPROBE_DEFER)
>>> -            return -EPROBE_DEFER;
>>> -        meson_dw_hdmi->hdmi_supply = NULL;
>>> -    } else {
>>> -        ret = regulator_enable(meson_dw_hdmi->hdmi_supply);
>>> -        if (ret)
>>> -            return ret;
>>> -        ret = devm_add_action_or_reset(dev, meson_disable_regulator,
>>> -                           meson_dw_hdmi->hdmi_supply);
>>> -        if (ret)
>>> -            return ret;
>>> -    }
>>> +    ret = devm_regulator_get_enable_optional(dev, "hdmi");
>>> +    if (ret != -ENODEV)
>>> +        return ret;
>>
>> As noted in the review of the series that introduced
>> devm_regulator_get_enable_optional(), the right thing to do is to
>> implement runtime PM in this driver to avoid wasting power.
> 
> While I agree, it's not really the same level of effort as this patch
> should be functionally equivalent.

While we all agree that power savings gained by runtime PM would be 
great - I don't think we should stop minor improvements while waiting 
for that to magically happen ;)

I like the saying I first heard from Jonathan Cameron - "Don't let the 
perfect be an enemy of good".

After that being said, should I re-spin this or just drop it? (I am 
cleaning up my local git from old stuff, and these are about to vanish 
from my books).

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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