linux-kernel - Re: [PATCH 5/5] drm/bridge: simple-bridge: Add next panel support

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Message-ID: <69dbfa41-31d9-41fb-9897-74735b3b5a3e@nxp.com>
Date: Thu, 6 Mar 2025 14:17:13 +0800
From: Liu Ying <victor.liu@....com>
To: Maxime Ripard <mripard@...nel.org>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, andrzej.hajda@...el.com, neil.armstrong@...aro.org,
 rfoss@...nel.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
 tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch
Subject: Re: [PATCH 5/5] drm/bridge: simple-bridge: Add next panel support

On 03/04/2025, Maxime Ripard wrote:
> On Tue, Mar 04, 2025 at 06:15:30PM +0800, Liu Ying wrote:
>> The next bridge connected to a simple bridge could be a panel, e.g.,
>> a DPI panel connected to a DPI color encoder. Add the next panel support,
>> instead of supporting non-panel next bridge only.
>>
>> Signed-off-by: Liu Ying <victor.liu@....com>
>> ---
>>  drivers/gpu/drm/bridge/Kconfig         |  1 +
>>  drivers/gpu/drm/bridge/simple-bridge.c | 32 ++++++++++++++++----------
>>  2 files changed, 21 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
>> index d20f1646dac2..92187dbdd32b 100644
>> --- a/drivers/gpu/drm/bridge/Kconfig
>> +++ b/drivers/gpu/drm/bridge/Kconfig
>> @@ -310,6 +310,7 @@ config DRM_SIMPLE_BRIDGE
>>  	tristate "Simple DRM bridge support"
>>  	depends on OF
>>  	select DRM_KMS_HELPER
>> +	select DRM_PANEL_BRIDGE
>>  	help
>>  	  Support for non-programmable DRM bridges, such as ADI ADV7123, TI
>>  	  THS8134 and THS8135 or passive resistor ladder DACs.
>> diff --git a/drivers/gpu/drm/bridge/simple-bridge.c b/drivers/gpu/drm/bridge/simple-bridge.c
>> index c0445bd20e07..4c585e5583ca 100644
>> --- a/drivers/gpu/drm/bridge/simple-bridge.c
>> +++ b/drivers/gpu/drm/bridge/simple-bridge.c
>> @@ -19,6 +19,7 @@
>>  #include <drm/drm_crtc.h>
>>  #include <drm/drm_edid.h>
>>  #include <drm/drm_of.h>
>> +#include <drm/drm_panel.h>
>>  #include <drm/drm_print.h>
>>  #include <drm/drm_probe_helper.h>
>>  
>> @@ -35,6 +36,7 @@ struct simple_bridge {
>>  	const struct simple_bridge_info *info;
>>  
>>  	struct drm_bridge	*next_bridge;
>> +	struct drm_panel	*next_panel;
>>  	struct regulator	*vdd;
>>  	struct gpio_desc	*enable;
>>  
>> @@ -114,6 +116,10 @@ static int simple_bridge_attach(struct drm_bridge *bridge,
>>  	struct simple_bridge *sbridge = drm_bridge_to_simple_bridge(bridge);
>>  	int ret;
>>  
>> +	if (sbridge->next_panel)
>> +		return drm_bridge_attach(bridge->encoder, sbridge->next_bridge,
>> +					 bridge, flags);
>> +
>>  	ret = drm_bridge_attach(bridge->encoder, sbridge->next_bridge, bridge,
>>  				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>>  	if (ret < 0)
>> @@ -247,7 +253,6 @@ static int simple_bridge_get_dpi_color_coding(struct simple_bridge *sbridge,
>>  static int simple_bridge_probe(struct platform_device *pdev)
>>  {
>>  	struct simple_bridge *sbridge;
>> -	struct device_node *remote;
>>  	int ret;
>>  
>>  	sbridge = devm_kzalloc(&pdev->dev, sizeof(*sbridge), GFP_KERNEL);
>> @@ -257,17 +262,20 @@ static int simple_bridge_probe(struct platform_device *pdev)
>>  	sbridge->info = of_device_get_match_data(&pdev->dev);
>>  
>>  	/* Get the next bridge in the pipeline. */
>> -	remote = of_graph_get_remote_node(pdev->dev.of_node, 1, -1);
>> -	if (!remote)
>> -		return -EINVAL;
>> -
>> -	sbridge->next_bridge = of_drm_find_bridge(remote);
>> -	of_node_put(remote);
>> -
>> -	if (!sbridge->next_bridge) {
>> -		dev_dbg(&pdev->dev, "Next bridge not found, deferring probe\n");
>> -		return -EPROBE_DEFER;
>> -	}
>> +	ret = drm_of_find_panel_or_bridge(pdev->dev.of_node, 1, -1,
>> +					  &sbridge->next_panel,
>> +					  &sbridge->next_bridge);
>> +	if (ret)
>> +		return dev_err_probe(&pdev->dev, ret,
>> +				     "Next panel or bridge not found\n");
>> +
>> +	if (sbridge->next_panel)
>> +		sbridge->next_bridge = devm_drm_panel_bridge_add(&pdev->dev,
>> +								 sbridge->next_panel);
>> +
>> +	if (IS_ERR(sbridge->next_bridge))
>> +		return dev_err_probe(&pdev->dev, PTR_ERR(sbridge->next_bridge),
>> +				     "Next bridge not found\n");
> 
> This makes sense in general, but I think a better approach would be to
> use devm/drmm_of_get_bridge here.

I chose to open-code devm_of_get_bridge() because sbridge->next_panel can
be grabbed and used to determine the logics in simple_bridge_attach() and
the flags handled over to drm_bridge_attach().

However, if a separate driver is needed for the DPI color encoder, I won't
touch this driver.

> 
> Maxime

-- 
Regards,
Liu Ying