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Date: Mon, 8 Apr 2024 13:23:58 +0200
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Subject: Re: [PATCH 1/2] media: dvbdev: make dvb_class constant
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To: "Ricardo B. Marliere" <ricardo@marliere.net>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>, Sean Young <sean@mess.org>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240305-class_cleanup-media-v1-0-53e1538973cd@marliere.net>
 <20240305-class_cleanup-media-v1-1-53e1538973cd@marliere.net>
 <ae5840f3-7e19-4d60-bd87-567068a3f813@xs4all.nl>
 <iduap7j36flhvmmsbvm6kzormftqi2xxfpndf62jp5lveljo3k@zgpxyqwckuuz>
From: Hans Verkuil <hverkuil@xs4all.nl>
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On 08/04/2024 12:47, Ricardo B. Marliere wrote:
> Hi Hans!
> 
> On  8 Apr 11:47, Hans Verkuil wrote:
>> On 05/03/2024 14:26, Ricardo B. Marliere wrote:
>>> Since commit 43a7206b0963 ("driver core: class: make class_register() take
>>> a const *"), the driver core allows for struct class to be in read-only
>>> memory, so move the dvb_class structure to be declared at build time
>>> placing it into read-only memory, instead of having to be dynamically
>>> allocated at boot time.
>>>
>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
>>> ---
>>>  drivers/media/dvb-core/dvbdev.c | 23 +++++++++++++----------
>>>  1 file changed, 13 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
>>> index 733d0bc4b4cc..dcbf68b00240 100644
>>> --- a/drivers/media/dvb-core/dvbdev.c
>>> +++ b/drivers/media/dvb-core/dvbdev.c
>>> @@ -78,7 +78,13 @@ static const u8 minor_type[] = {
>>>  #define MAX_DVB_MINORS		(DVB_MAX_ADAPTERS * 64)
>>>  #endif
>>>  
>>> -static struct class *dvb_class;
>>> +static int dvb_uevent(const struct device *dev, struct kobj_uevent_env *env);
>>> +static char *dvb_devnode(const struct device *dev, umode_t *mode);
>>
>> Forward references are typically something you want to avoid.
>>
>> Looking at the code, I think it makes sense to just move those two functions
>> to just before this dvb_class.
> 
> Ack.
> 
>>
>>> +static const struct class dvb_class = {
>>> +	.name = "dvb",
>>> +	.dev_uevent = dvb_uevent,
>>> +	.devnode = dvb_devnode,
>>> +};
>>>  
>>>  static struct dvb_device *dvb_minors[MAX_DVB_MINORS];
>>>  static DECLARE_RWSEM(minor_rwsem);
>>
>> Also move the dvb_class (+ the two functions) to after this line. I think that's
>> a more suitable place for this.
> 
> Ack.
> 
>>
>>> @@ -561,7 +567,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
>>>  		return ret;
>>>  	}
>>>  
>>> -	clsdev = device_create(dvb_class, adap->device,
>>> +	clsdev = device_create(&dvb_class, adap->device,
>>>  			       MKDEV(DVB_MAJOR, minor),
>>>  			       dvbdev, "dvb%d.%s%d", adap->num, dnames[type], id);
>>>  	if (IS_ERR(clsdev)) {
>>> @@ -600,7 +606,7 @@ void dvb_remove_device(struct dvb_device *dvbdev)
>>>  
>>>  	dvb_media_device_free(dvbdev);
>>>  
>>> -	device_destroy(dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
>>> +	device_destroy(&dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
>>>  
>>>  	list_del(&dvbdev->list_head);
>>>  }
>>> @@ -1096,13 +1102,10 @@ static int __init init_dvbdev(void)
>>>  		goto error;
>>>  	}
>>>  
>>> -	dvb_class = class_create("dvb");
>>> -	if (IS_ERR(dvb_class)) {
>>> -		retval = PTR_ERR(dvb_class);
>>> +	retval = class_register(&dvb_class);
>>> +	if (retval != 0)
>>
>> This can just be 'if (retval)'.
> 
> But then it would be on a different style than the rest of the function:

Ah, I hadn't noticed that. Let's keep it as you proposed then.

Regards,

	Hans

> 
> static int __init init_dvbdev(void)
> {
> 	int retval;
> 	dev_t dev = MKDEV(DVB_MAJOR, 0);
> 
> 	retval = register_chrdev_region(dev, MAX_DVB_MINORS, "DVB");
> 	if (retval != 0) {
> 		pr_err("dvb-core: unable to get major %d\n", DVB_MAJOR);
> 		return retval;
> 	}
> 
> 	cdev_init(&dvb_device_cdev, &dvb_device_fops);
> 	retval = cdev_add(&dvb_device_cdev, dev, MAX_DVB_MINORS);
> 	if (retval != 0) {
> 		pr_err("dvb-core: unable register character device\n");
> 		goto error;
> 	}
> 
> 	retval = class_register(&dvb_class);
> 	if (retval != 0)
> 		goto error;
> 
> 	return 0;
> 
> error:
> 	cdev_del(&dvb_device_cdev);
> 	unregister_chrdev_region(dev, MAX_DVB_MINORS);
> 	return retval;
> }
> 
> 
>>
>>>  		goto error;
>>> -	}
>>> -	dvb_class->dev_uevent = dvb_uevent;
>>> -	dvb_class->devnode = dvb_devnode;
>>> +
>>>  	return 0;
>>>  
>>>  error:
>>> @@ -1115,7 +1118,7 @@ static void __exit exit_dvbdev(void)
>>>  {
>>>  	struct dvbdevfops_node *node, *next;
>>>  
>>> -	class_destroy(dvb_class);
>>> +	class_unregister(&dvb_class);
>>>  	cdev_del(&dvb_device_cdev);
>>>  	unregister_chrdev_region(MKDEV(DVB_MAJOR, 0), MAX_DVB_MINORS);
>>>  
>>>
>>
>> Regards,
>>
>> 	Hans