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Message-ID: <910325b6-2a0a-40ae-82c2-656fcbb0d060@nxp.com>
Date: Thu, 5 Feb 2026 17:26:45 +0800
From: Liu Ying <victor.liu@....com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Fabio Estevam <festevam@...il.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, Ian Ray <ian.ray@...ealthcare.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next
bridge
On Thu, Feb 05, 2026 at 09:52:04AM +0100, Luca Ceresoli wrote:
> Hello Liu,
Hello Luca,
>
> On Wed Feb 4, 2026 at 7:27 AM CET, Liu Ying wrote:
>> Hi Luca,
>>
>> On Tue, Feb 03, 2026 at 11:35:25AM +0100, Luca Ceresoli wrote:
>>> This driver obtains a bridge pointer from of_drm_find_bridge() in the probe
>>> function and stores it until driver removal. of_drm_find_bridge() is
>>> deprecated. Move to of_drm_find_and_get_bridge() for the bridge to be
>>> refcounted and use bridge->next_bridge to put the reference on
>>> deallocation.
>>>
>>> To keep the code as simple and reliable as possible, get a reference for
>>> each pointer that stores a drm_bridge address when it is stored and release
>>> it when the pointer is overwritten or goes out of scope. Also remove the
>>> intermediate selected_bridge variable to reduce the refcounted variables in
>>> the function. The involved pointers are:
>>>
>>> * next_bridge loop-local variable:
>>> - get reference by of_drm_find_and_get_bridge()
>>> - put reference at the end of the loop iteration (__free)
>>>
>>> * pl->bridge.next_bridge, tied to struct imx8qxp_pixel_link lifetime:
>>> - get reference when assigned (by copy from next_bridge)
>>> - put reference before reassignment if reassignment happens
>>> - put reference when the struct imx8qxp_pixel_link embedding the
>>> struct drm_bridge is destroyed (struct drm_bridge::next_bridge)
>>>
>>> Additionally, split the somewhat complex if() for readability.
>>>
>>> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
>>>
>>> ---
>>>
>>> Changes in v5:
>>> - rewrite commit message after Liu's review to clarify the per-pointer
>>> get/put idea
>>> - split the if()s involved in selcting the bridge
>>> - remove intermediate selected_bridge pointer
>>> - removed Maxime's R-by, patch changed
>>> ---
>>> drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 17 ++++++++++-------
>>> 1 file changed, 10 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
>>> index 91e4f4d55469..e29e099b893a 100644
>>> --- a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
>>> +++ b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
>>> @@ -23,7 +23,6 @@
>>>
>>> struct imx8qxp_pixel_link {
>>> struct drm_bridge bridge;
>>> - struct drm_bridge *next_bridge;
>>> struct device *dev;
>>> struct imx_sc_ipc *ipc_handle;
>>> u8 stream_id;
>>> @@ -140,7 +139,7 @@ static int imx8qxp_pixel_link_bridge_attach(struct drm_bridge *bridge,
>>> }
>>>
>>> return drm_bridge_attach(encoder,
>>> - pl->next_bridge, bridge,
>>> + pl->bridge.next_bridge, bridge,
>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>>> }
>>>
>>> @@ -260,7 +259,6 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>>> {
>>> struct device_node *np = pl->dev->of_node;
>>> struct device_node *port;
>>> - struct drm_bridge *selected_bridge = NULL;
>>> u32 port_id;
>>> bool found_port = false;
>>> int reg;
>>> @@ -297,7 +295,8 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>>> continue;
>>> }
>>>
>>> - struct drm_bridge *next_bridge = of_drm_find_bridge(remote);
>>> + struct drm_bridge *next_bridge __free(drm_bridge_put) =
>>> + of_drm_find_and_get_bridge(remote);
>>> if (!next_bridge)
>>> return -EPROBE_DEFER;
>>>
>>> @@ -305,12 +304,16 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>>> * Select the next bridge with companion PXL2DPI if
>>> * present, otherwise default to the first bridge
>>> */
>>> - if (!selected_bridge || of_property_present(remote, "fsl,companion-pxl2dpi"))
>>> - selected_bridge = next_bridge;
>>> + if (!pl->bridge.next_bridge)
>>> + pl->bridge.next_bridge = drm_bridge_get(next_bridge);
>>> +
>>> + if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
>>> + drm_bridge_put(pl->bridge.next_bridge);
>>> + pl->bridge.next_bridge = drm_bridge_get(next_bridge);
>>> + }
>>
>> Can you drop the intermediate next_bridge variable to simplify the code?
>>
>> -8<-
>> if (!pl->bridge.next_bridge) {
>> pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>> if (!pl->bridge.next_bridge)
>> return -EPROBE_DEFER;
>> }
>>
>> if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
>> drm_bridge_put(pl->bridge.next_bridge);
>> pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>> if (!pl->bridge.next_bridge)
>> return -EPROBE_DEFER;
>> }
>> -8<-
>
> Potentially calling of_drm_find_and_get_bridge() twice on the same node,
> with a put in the middle, looks poorly readable to me, even though it still
> looks correct code.
>
> However I think we can do even better with an 'else if':
>
> if (!pl->bridge.next_bridge) {
> pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
> if (!pl->bridge.next_bridge)
> return -EPROBE_DEFER;
> } else if (of_property_present(remote, "fsl,companion-pxl2dpi")) { <===
> drm_bridge_put(pl->bridge.next_bridge);
> pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
> if (!pl->bridge.next_bridge)
> return -EPROBE_DEFER;
> }
>
> Looks OK?
Both are fine to me. TBH, I feel my version with two 'if's is a bit easier
to read. But, I'd say up to you.
>
> Luca
>
> --
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com/
--
Regards,
Liu Ying
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