Re: [PATCH v3] drm/bridge: analogix_dp: use devm_phy_optional_get() for the DP PHY

From: "Luca Ceresoli" <luca.ceresoli@bootlin.com>
To: "Jun Yan" <jerrysteve1101@gmail.com>, <damon.ding@rock-chips.com>
Cc: <Laurent.pinchart@ideasonboard.com>, <airlied@gmail.com>,
	<andrzej.hajda@intel.com>, <dri-devel@lists.freedesktop.org>,
	<heiko@sntech.de>, <jernej.skrabec@gmail.com>, <jonas@kwiboo.se>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-rockchip@lists.infradead.org>, <luca.ceresoli@bootlin.com>,
	<maarten.lankhorst@linux.intel.com>, <mripard@kernel.org>,
	<neil.armstrong@linaro.org>, <rfoss@kernel.org>,
	<simona@ffwll.ch>, <tzimmermann@suse.de>
Subject: Re: [PATCH v3] drm/bridge: analogix_dp: use devm_phy_optional_get() for the DP PHY
Date: Fri, 13 Nov 2026 16:41:56 +0100	[thread overview]
Message-ID: <DMU749TMB523.3OCGPYVI4NZDU@bootlin.com> (raw)
In-Reply-To: <20261113131248.2804840-1-jerrysteve1101@gmail.com>

Hello,

On Fri Nov 13, 2026 at 2:12 PM CET, Jun Yan wrote:
> Hi Damon,
>
>> You are right, this is really a valid concern.
>>
>> If CONFIG_GENERIC_PHY is disabled, the old code could still proceed and
>> keep the driver probing, while the new version would return an error
>> directly.
>
> -ENOSYS can only come from the !CONFIG_GENERIC_PHY stubs in
> include/linux/phy/phy.h; the real implementation in drivers/phy/phy-core.c
> never returns it. And the stub for the optional variant returns NULL, not
> -ENOSYS:
>
>     static inline struct phy *devm_phy_optional_get(struct device *dev,
>                                                     const char *string)
>     {
>             return NULL;
>     }
>
> So with CONFIG_GENERIC_PHY disabled the PHY is still treated as absent
> (NULL), exactly as the old -ENOSYS branch did. With CONFIG_GENERIC_PHY
> enabled, -ENOSYS cannot occur, devm_phy_optional_get() turns -ENODEV into
> NULL, and any other error is still propagated - same as the open-coded
> check.
>
>> It should be better to keep the -ENOSYS handling to preserve the
>> original behavior.
>
> Overall the behaviour is unchanged in both configurations, so no separate
> handling is needed.

Thanks for the analysis! Cna you send a v4 with that explained in the
commit message, possibly in a more concise way, maybe with bullets for the
various CONFIG_GENERIC_PHY on/off cases or so, for readability?

Reading it now, this v3 commit message kind of said the same things. but it
misled both me and Damon, so it's worth a clear explanation.

Thanks!

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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