linux-kernel - Re: [PATCH] drm/sun4i: Clear encoder->bridge if a bridge is not found

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Message-ID: <CAGb2v67hiYhjQNXLZUz7ZT2214AAYsFwQkg42qKEFv-7kShsQQ@mail.gmail.com>
Date:   Wed, 31 Aug 2016 19:09:23 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/sun4i: Clear encoder->bridge if a bridge is not found

Hi Maxime,

On Tue, Aug 30, 2016 at 11:51 PM, Chen-Yu Tsai <wens@...e.org> wrote:
> On Tue, Aug 30, 2016 at 8:56 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
>> Hi,
>>
>> On Tue, Aug 30, 2016 at 08:22:23PM +0800, Chen-Yu Tsai wrote:
>>> The KMS helpers (drm_atomic_helper_check_modeset/mode_fixup) pass
>>> encoder->bridge directly to drm_bridge_mode_fixup, which expects a
>>> valid pointer, or NULL (in which case it just returns).
>>>
>>> Clear encoder->bridge if a bridge is not found, instead of keeping
>>> the ERR_PTR value.
>>>
>>> Since other drm_bridge functions also follow this pattern of checking
>>> for a non-NULL pointer, we can drop the ifs around the calls and just
>>> pass the pointer directly.
>>>
>>> Fixes: 894f5a9f4b4a ("drm/sun4i: Add bridge support")
>>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>>> ---
>>>  drivers/gpu/drm/sun4i/sun4i_rgb.c | 11 ++++++-----
>>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/sun4i/sun4i_rgb.c b/drivers/gpu/drm/sun4i/sun4i_rgb.c
>>> index d4e52522ec53..ee0795152a33 100644
>>> --- a/drivers/gpu/drm/sun4i/sun4i_rgb.c
>>> +++ b/drivers/gpu/drm/sun4i/sun4i_rgb.c
>>> @@ -154,8 +154,7 @@ static void sun4i_rgb_encoder_enable(struct drm_encoder *encoder)
>>>       if (!IS_ERR(tcon->panel))
>>>               drm_panel_enable(tcon->panel);
>>>
>>> -     if (!IS_ERR(encoder->bridge))
>>> -             drm_bridge_enable(encoder->bridge);
>>> +     drm_bridge_enable(encoder->bridge);
>>>
>>>       sun4i_tcon_channel_enable(tcon, 0);
>>>  }
>>> @@ -170,8 +169,7 @@ static void sun4i_rgb_encoder_disable(struct drm_encoder *encoder)
>>>
>>>       sun4i_tcon_channel_disable(tcon, 0);
>>>
>>> -     if (!IS_ERR(encoder->bridge))
>>> -             drm_bridge_disable(encoder->bridge);
>>> +     drm_bridge_disable(encoder->bridge);
>>
>> I'd rather keep those changes, it makes it obvious that it's something
>> optionnal, that can be set to NULL.
>
> OK.

What about having a comment instead? Saves an extra branch condition,
while still showing that it's optional.

ChenYu

>
>>>       if (!IS_ERR(tcon->panel))
>>>               drm_panel_disable(tcon->panel);
>>> @@ -230,6 +228,9 @@ int sun4i_rgb_init(struct drm_device *drm)
>>>               return 0;
>>>       }
>>>
>>> +     if (IS_ERR(encoder->bridge))
>>> +             encoder->bridge = NULL;
>>> +
>>
>> And that could be the else condition of the if statement below.
>
> That would be a bit confusing, changing it after calling drm_encoder_init.
> The code says it ok to do though.
>
> ChenYu
>
>> Thanks!
>> Maxime
>>
>> --
>> Maxime Ripard, Free Electrons
>> Embedded Linux and Kernel engineering
>> http://free-electrons.com