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Message-ID: <cd81893c-ef0b-4906-8c9c-a98b1e4669e6@linux.dev>
Date: Wed, 15 May 2024 18:17:52 +0800
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MIME-Version: 1.0
Subject: Re: [PATCH 1/2] drm/bridge: Support finding bridge with struct device
To: Jani Nikula <jani.nikula@linux.intel.com>,
 Neil Armstrong <neil.armstrong@linaro.org>,
 Maxime Ripard <mripard@kernel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20240514154045.309925-1-sui.jingfeng@linux.dev>
 <20240514154045.309925-2-sui.jingfeng@linux.dev> <87v83fct2e.fsf@intel.com>
Content-Language: en-US, en-AU
From: Sui Jingfeng <sui.jingfeng@linux.dev>
In-Reply-To: <87v83fct2e.fsf@intel.com>
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Hi,


On 5/15/24 17:39, Jani Nikula wrote:
> On Tue, 14 May 2024, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>> The pointer of 'struct device' can also be used as a key to search drm
>> bridge instance from the global bridge list, traditionally, fwnode and
>> 'OF' based APIs requires the system has decent fwnode/OF Graph support.
>> While the drm_find_bridge_by_dev() function introduced in this series
>> don't has such a restriction. It only require you has a pointer to the
>> backing device. Hence, it may suitable for some small and/or limited
>> display subsystems.
>>
>> Also add the drm_bridge_add_with_dev() as a helper, which automatically
>> set the .of_node field of drm_bridge instances if you call it. But it
>> suitable for simple bridge drivers which one device backing one drm_bridge
>> instance.
>>
>> Signed-off-by: Sui Jingfeng <sui.jingfeng@linux.dev>
>> ---
>>   drivers/gpu/drm/drm_bridge.c | 39 ++++++++++++++++++++++++++++++++++++
>>   include/drm/drm_bridge.h     |  5 +++++
>>   2 files changed, 44 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>> index 584d109330ab..1928d9d0dd3c 100644
>> --- a/drivers/gpu/drm/drm_bridge.c
>> +++ b/drivers/gpu/drm/drm_bridge.c
>> @@ -213,6 +213,23 @@ void drm_bridge_add(struct drm_bridge *bridge)
>>   }
>>   EXPORT_SYMBOL(drm_bridge_add);
>>   
>> +/**
>> + * drm_bridge_add_with_dev - add the given bridge to the global bridge list
>> + *
>> + * @bridge: bridge control structure
>> + * @dev: pointer to the kernel device that this bridge is backed.
>> + */
>> +void drm_bridge_add_with_dev(struct drm_bridge *bridge, struct device *dev)
>> +{
>> +	if (dev) {
>> +		bridge->kdev = dev;
>> +		bridge->of_node = dev->of_node;
>> +	}
>> +
>> +	drm_bridge_add(bridge);
>> +}
>> +EXPORT_SYMBOL_GPL(drm_bridge_add_with_dev);
> 
> I don't actually have an opinion on whether the dev parameter is useful
> or not.
> 
> But please don't add a drm_bridge_add_with_dev() and then convert more
> than half the drm_bridge_add() users to that. Please just add a struct
> device *dev parameter to drm_bridge_add(), and pass NULL if it's not
> relevant.
> 

To be honest, previously, I'm just do it exactly same as the way you
told me here. But I'm exhausted and finally give up.

Because this is again need me to modify *all* callers of 
drm_bridge_add(), not only those bridges in drm/bridge/, but also
bridge instances in various KMS drivers.

However, their some exceptions just don't fit!

For example, the imx/imx8qxp-pixel-combiner.c just don't fit our
simple model. Our helper function assume that one device backing
one drm_bridge instance (1 to 1). Yet, that driver backing two or
more bridges with one platform device (1 to 2, 1 to 3, ..., ).
Hence, the imx/imx8qxp-pixel-combiner.c just can't use 
drm_bridge_add_with_dev().

The aux_hpd_bridge.c is also bad, it store the of_node of struct device 
at the .platform_data member of the struct device.

> BR,
> Jani.
> 
> 
>> +
>>   static void drm_bridge_remove_void(void *bridge)
>>   {
>>   	drm_bridge_remove(bridge);
>> @@ -1334,6 +1351,27 @@ void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>>   }
>>   EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
>>   
>> +struct drm_bridge *drm_find_bridge_by_dev(struct device *kdev)
>> +{
>> +	struct drm_bridge *bridge;
>> +
>> +	if (!kdev)
>> +		return NULL;
>> +
>> +	mutex_lock(&bridge_lock);
>> +
>> +	list_for_each_entry(bridge, &bridge_list, list) {
>> +		if (bridge->kdev == kdev) {
>> +			mutex_unlock(&bridge_lock);
>> +			return bridge;
>> +		}
>> +	}
>> +
>> +	mutex_unlock(&bridge_lock);
>> +	return NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(drm_find_bridge_by_dev);
>> +
>>   #ifdef CONFIG_OF
>>   /**
>>    * of_drm_find_bridge - find the bridge corresponding to the device node in
>> @@ -1361,6 +1399,7 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
>>   	return NULL;
>>   }
>>   EXPORT_SYMBOL(of_drm_find_bridge);
>> +
>>   #endif
>>   
>>   MODULE_AUTHOR("Ajay Kumar <ajaykumar.rs@samsung.com>");
>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>> index 4baca0d9107b..70d8393bbd9c 100644
>> --- a/include/drm/drm_bridge.h
>> +++ b/include/drm/drm_bridge.h
>> @@ -715,6 +715,8 @@ struct drm_bridge {
>>   	struct drm_private_obj base;
>>   	/** @dev: DRM device this bridge belongs to */
>>   	struct drm_device *dev;
>> +	/** @kdev: pointer to the kernel device backing this bridge */
>> +	struct device *kdev;
>>   	/** @encoder: encoder to which this bridge is connected */
>>   	struct drm_encoder *encoder;
>>   	/** @chain_node: used to form a bridge chain */
>> @@ -782,12 +784,15 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
>>   }
>>   
>>   void drm_bridge_add(struct drm_bridge *bridge);
>> +void drm_bridge_add_with_dev(struct drm_bridge *bridge, struct device *dev);
>>   int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge);
>>   void drm_bridge_remove(struct drm_bridge *bridge);
>>   int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>>   		      struct drm_bridge *previous,
>>   		      enum drm_bridge_attach_flags flags);
>>   
>> +struct drm_bridge *drm_find_bridge_by_dev(struct device *kdev);
>> +
>>   #ifdef CONFIG_OF
>>   struct drm_bridge *of_drm_find_bridge(struct device_node *np);
>>   #else
> 

-- 
Best regards
Sui