linux-kernel - Re: [PATCH v10 03/11] drm/etnaviv: Add dedicated functions to create and destroy platform device

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Date:   Wed, 21 Jun 2023 17:49:39 +0800
From:   Sui Jingfeng <suijingfeng@...ngson.cn>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Sui Jingfeng <18949883232@....com>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        etnaviv@...ts.freedesktop.org,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v10 03/11] drm/etnaviv: Add dedicated functions to create
 and destroy platform device

Hi

On 2023/6/21 17:15, Lucas Stach wrote:
> Am Dienstag, dem 20.06.2023 um 17:47 +0800 schrieb Sui Jingfeng:
>> From: Sui Jingfeng <suijingfeng@...ngson.cn>
>>
>> Also rename the virtual master platform device as etnaviv_platform_device,
>> for better reflection that it is a platform device, not a DRM device.
>>
>> Another benefit is that we no longer need to call of_node_put() for three
>> different cases, Instead, we only need to call it once.
>>
>> Cc: Lucas Stach <l.stach@...gutronix.de>
>> Cc: Christian Gmeiner <christian.gmeiner@...il.com>
>> Cc: Philipp Zabel <p.zabel@...gutronix.de>
>> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> ---
>>   drivers/gpu/drm/etnaviv/etnaviv_drv.c | 56 +++++++++++++++++++--------
>>   1 file changed, 39 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>> index 31a7f59ccb49..cec005035d0e 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>> @@ -656,12 +656,44 @@ static struct platform_driver etnaviv_platform_driver = {
>>   	},
>>   };
>>   
>> -static struct platform_device *etnaviv_drm;
>> +static struct platform_device *etnaviv_platform_device;
>>   
>> -static int __init etnaviv_init(void)
>> +static int etnaviv_create_platform_device(const char *name,
>> +					  struct platform_device **ppdev)
> As the platform device is a global static variable, there is no need to
> push it through the parameters of this function. Just use the global
> variable directly in this function.

A function reference a global static variable is *NOT* a *pure* fucntion,

it degenerate as a procedure,


The function is perfect in the sense that it does not reference any 
global variable.


etnaviv_create_platform_device() is NOT intended to used by one function,

a specific purpose only, but when create this function, I want to create other

platform device with this function.

Say, You want to create a dummy platform device, targeting to bind to the real master

(the single GPU core) . To verify the idea that we choose the first 3D gpu core as master,

other 2D or VG gpu core is not as important as the 3D one.

The should bind to the 3D GPU core (master).


While back to the question you ask, I want etnaviv_create_platform_device() to be generic,

can be used by multiple place for multiple purpose.

I have successfully copy this to a another drm driver by simply renaming.

The body of the function itself does not need to change.

>>   {
>>   	struct platform_device *pdev;
>>   	int ret;
>> +
>> +	pdev = platform_device_alloc(name, PLATFORM_DEVID_NONE);
>> +	if (!pdev)
>> +		return -ENOMEM;
>> +
>> +	ret = platform_device_add(pdev);
>> +	if (ret) {
>> +		platform_device_put(pdev);
>> +		return ret;
>> +	}
>> +
>> +	*ppdev = pdev;
>> +
>> +	return 0;
>> +}
>> +
>> +static void etnaviv_destroy_platform_device(struct platform_device **ppdev)
>> +{
>> +	struct platform_device *pdev = *ppdev;
> Same here, just use the global variable directly.
>
> Regards,
> Lucas
>
>> +
>> +	if (!pdev)
>> +		return;
>> +
>> +	platform_device_unregister(pdev);
>> +
>> +	*ppdev = NULL;
>> +}
>> +
>> +static int __init etnaviv_init(void)
>> +{
>> +	int ret;
>>   	struct device_node *np;
>>   
>>   	etnaviv_validate_init();
>> @@ -681,23 +713,13 @@ static int __init etnaviv_init(void)
>>   	for_each_compatible_node(np, NULL, "vivante,gc") {
>>   		if (!of_device_is_available(np))
>>   			continue;
>> +		of_node_put(np);
>>   
>> -		pdev = platform_device_alloc("etnaviv", PLATFORM_DEVID_NONE);
>> -		if (!pdev) {
>> -			ret = -ENOMEM;
>> -			of_node_put(np);
>> -			goto unregister_platform_driver;
>> -		}
>> -
>> -		ret = platform_device_add(pdev);
>> -		if (ret) {
>> -			platform_device_put(pdev);
>> -			of_node_put(np);
>> +		ret = etnaviv_create_platform_device("etnaviv",
>> +						     &etnaviv_platform_device);
>> +		if (ret)
>>   			goto unregister_platform_driver;
>> -		}
>>   
>> -		etnaviv_drm = pdev;
>> -		of_node_put(np);
>>   		break;
>>   	}
>>   
>> @@ -713,7 +735,7 @@ module_init(etnaviv_init);
>>   
>>   static void __exit etnaviv_exit(void)
>>   {
>> -	platform_device_unregister(etnaviv_drm);
>> +	etnaviv_destroy_platform_device(&etnaviv_platform_device);
>>   	platform_driver_unregister(&etnaviv_platform_driver);
>>   	platform_driver_unregister(&etnaviv_gpu_driver);
>>   }

-- 
Jingfeng