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Message-Id: <DG6WFD0WCCMQ.2AT7S8YHVLH7@bootlin.com>
Date: Thu, 05 Feb 2026 09:52:04 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Liu Ying" <victor.liu@....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
Hello Liu,
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?
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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