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

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Date:   Wed, 16 Nov 2022 13:23:00 +0100
From:   "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        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*()

On 16/11/2022 13:02, Vaittinen, Matti wrote:
> 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).

I'm ok with you, please re-spin it.

Neil

> 
> Yours,
> 	-- Matti
>