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Subject: Re: [PATCH v4 1/3] drm/panel: refactor INNOLUX P079ZCA panel driver
To:     Emil Velikov <emil.l.velikov@gmail.com>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Brian Norris <briannorris@chromium.org>,
        Rob Herring <robh+dt@kernel.org>,
        Sean Paul <seanpaul@chromium.org>,
        David Airlie <airlied@linux.ie>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        ML dri-devel <dri-devel@lists.freedesktop.org>
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From:   hl <hl@rock-chips.com>
Message-ID: <b2f89ae1-c028-b6ab-2ccd-6fb93161ea1f@rock-chips.com>
Date:   Thu, 22 Mar 2018 09:49:25 +0800
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Hi


On Tuesday, March 20, 2018 06:20 PM, Emil Velikov wrote:
> On 20 March 2018 at 06:24, hl <hl@rock-chips.com> wrote:
>> Hi Emil,
>>
>>
>>
>> On Monday, March 19, 2018 09:09 PM, Emil Velikov wrote:
>>> On 15 March 2018 at 02:35, hl <hl@rock-chips.com> wrote:
>>>> Hi Emil,
>>>>
>>>>
>>>>
>>>> On Wednesday, March 14, 2018 08:02 PM, Emil Velikov wrote:
>>>>> Hi Lin,
>>>>>
>>>>> On 14 March 2018 at 09:12, Lin Huang <hl@rock-chips.com> wrote:
>>>>>> From: huang lin <hl@rock-chips.com>
>>>>>>
>>>>>> Refactor Innolux P079ZCA panel driver, let it support
>>>>>> multi panel.
>>>>>>
>>>>>> Change-Id: If89be5e56dba8cb498e2d50c1bbeb0e8016123a2
>>>>>> Signed-off-by: Lin Huang <hl@rock-chips.com>
>>>>>> ---
>>>>>> Changes in v2:
>>>>>> - Change regulator property name to meet the panel datasheet
>>>>>> Changes in v3:
>>>>>> - this patch only refactor P079ZCA panel to support multi panel,
>>>>>> support
>>>>>> P097PFG panel in another patch
>>>>>> Changes in v4:
>>>>>> - Modify the patch which suggest by Thierry
>>>>>>
>>>>> Thanks for splitting this up. I think there's another piece that fell
>>>>> through the cracks.
>>>>> I'm not deeply familiar with the driver, so just sharing some quick
>>>>> notes.
>>>>>
>>>>>
>>>>>>     struct innolux_panel {
>>>>>>            struct drm_panel base;
>>>>>>            struct mipi_dsi_device *link;
>>>>>> +       const struct panel_desc *desc;
>>>>>>
>>>>>>            struct backlight_device *backlight;
>>>>>> -       struct regulator *supply;
>>>>>> +       struct regulator *vddi;
>>>>>> +       struct regulator *avdd;
>>>>>> +       struct regulator *avee;
>>>>> These two seem are new addition, as opposed to a dummy refactor.
>>>>> Are they optional, does one need them for the existing panel (separate
>>>>> patch?) or only for the new one (squash with the new panel code)?
>>>>>
>>>>>
>>>>>>            struct gpio_desc *enable_gpio;
>>>>>>
>>>>>>            bool prepared;
>>>>>> @@ -77,9 +93,9 @@ static int innolux_panel_unprepare(struct drm_panel
>>>>>> *panel)
>>>>>>            /* T8: 80ms - 1000ms */
>>>>>>            msleep(80);
>>>>>>
>>>>>> -       err = regulator_disable(innolux->supply);
>>>>>> -       if (err < 0)
>>>>>> -               return err;
>>>>> Good call on dropping the early return here.
>>>>>
>>>>>
>>>>>> @@ -207,19 +248,28 @@ static const struct drm_panel_funcs
>>>>>> innolux_panel_funcs = {
>>>>>> -       innolux->supply = devm_regulator_get(dev, "power");
>>>>>> -       if (IS_ERR(innolux->supply))
>>>>>> -               return PTR_ERR(innolux->supply);
>>>>>> +       innolux = devm_kzalloc(dev, sizeof(*innolux), GFP_KERNEL);
>>>>>> +       if (!innolux)
>>>>>> +               return -ENOMEM;
>>>>>> +
>>>>>> +       innolux->desc = desc;
>>>>>> +       innolux->vddi = devm_regulator_get(dev, "power");
>>>>>> +       innolux->avdd = devm_regulator_get(dev, "avdd");
>>>>>> +       innolux->avee = devm_regulator_get(dev, "avee");
>>>>>>
>>>>> AFAICT devm_regulator_get returns a pointer which is unsuitable to be
>>>>> passed into regulator_{enable,disable}.
>>>>> Hence, the IS_ERR check should stay. If any of the regulators are
>>>>> optional, you want to call regulator_{enable,disable} only as
>>>>> applicable.
>>>>
>>>> devm_regulator_get() will use dummy_regulator if there not regulator pass
>>>> to
>>>> driver, so it not affect regulator_{enable, disable}.
>>> One of us is getting confused here:
>>> devm_regulator_get does not _use_ a regulator, it returns a pointer to
>>> a regulator, right?
>>>
>>> According to the 4.16-rc6 codebase - one error
>>> returns a ERR_PTR [1].
>> devm_regulator_get() will not reurn a ERR_PTR,  it will pass NORMAL_GET mode
>> to
>> _regulator_get() when you call devm_regulator_get(), and with following
>> code:
>>
> Just before the _regulator_get() call we have "return ERR_PTR(-ENOMEM);"
> See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/regulator/devres.c?h=v4.16-rc6#n34
Okay, i got what you concern now, yes, you are right, i will keep IS_ERR 
checking here.
>
>>> With the pointer dereferenced in regulator_enable [2], without a
>>> IS_ERR check, hence thing will go boom(?)
>>>
>>>> These three regulator are
>>>> optional,
>>>> the p079zca will use "power" and ,
>>>> so i think it better not to check ERR here.
>>>>
>>> What should happen if p079zca is missing "power" or p097pgf - "avdd" and
>>> "avee"?
>>> Obviously the latter two should be introduced with the p097pgf support.
>> i think it need dts to make sure configure the power node correct, if
>> missing
>> "power" node fo p079zca or "avdd" "avee" node for p097pgf, the panel can
>> not work, but do not affcet other driver, the kernel do not crash(as i
>> explain before and i also test it).
>>
> If you know it won't work just don't continue? And yes, it will crash ;-)
> Either way, if you don't like my feedback so be it.
>
> HTH
> Emil
> P.S. As a non native English speaker to another - spell checker helps a lot ;-)
>
>
>