Re: [PATCH v3 04/10] drm/fbdev-generic: Initialize fb-helper structure in generic setup

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 25.01.23 um 22:03 schrieb Sam Ravnborg:
> Hi Thomas,
> 
> On Wed, Jan 25, 2023 at 09:04:09PM +0100, Thomas Zimmermann wrote:
>> Initialize the fb-helper structure immediately after its allocation
>> in drm_fbdev_generic_setup(). That will make it easier to fill it with
>> driver-specific values, such as the preferred BPP.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
>> ---
>>   drivers/gpu/drm/drm_fbdev_generic.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c
>> index 135d58b8007b..63f66325a8a5 100644
>> --- a/drivers/gpu/drm/drm_fbdev_generic.c
>> +++ b/drivers/gpu/drm/drm_fbdev_generic.c
>> @@ -385,8 +385,6 @@ static int drm_fbdev_client_hotplug(struct drm_client_dev *client)
>>   	if (dev->fb_helper)
>>   		return drm_fb_helper_hotplug_event(dev->fb_helper);
>>   
>> -	drm_fb_helper_prepare(dev, fb_helper, &drm_fb_helper_generic_funcs);
>> -
>>   	ret = drm_fb_helper_init(dev, fb_helper);
>>   	if (ret)
>>   		goto err;
> 
>  From the documentation:
> The drm_fb_helper_prepare()
> helper must be called first to initialize the minimum required to make
> hotplug detection work.
> ...
> To finish up the fbdev helper initialization, the
> drm_fb_helper_init() function is called.
> 
> So this change do not follow the documentation as drm_fb_helper_init()
> is now called before drm_fb_helper_prepare()

No, we now call drm_fb_helper_prepare() from within 
drm_fbdev_generic_setup(), right after allocating the fb_helper. 
drm_fb_helper_init() will only be called after the client received a 
hot-plug event.

> 
> I did not follow all the code - but my gut feeling is that the
> documentation is right.

The docs are of low quality. The _prepare() helper is the actual init 
function and _init() only sets the fb_helper in the device instance.

Best regards
Thomas

> 
> 	Sam
> 
> 
>> @@ -456,12 +454,12 @@ void drm_fbdev_generic_setup(struct drm_device *dev,
>>   	fb_helper = kzalloc(sizeof(*fb_helper), GFP_KERNEL);
>>   	if (!fb_helper)
>>   		return;
>> +	drm_fb_helper_prepare(dev, fb_helper, &drm_fb_helper_generic_funcs);
>>   
>>   	ret = drm_client_init(dev, &fb_helper->client, "fbdev", &drm_fbdev_client_funcs);
>>   	if (ret) {
>> -		kfree(fb_helper);
>>   		drm_err(dev, "Failed to register client: %d\n", ret);
>> -		return;
>> +		goto err_drm_client_init;
>>   	}
>>   
>>   	/*
>> @@ -484,5 +482,12 @@ void drm_fbdev_generic_setup(struct drm_device *dev,
>>   		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
>>   
>>   	drm_client_register(&fb_helper->client);
>> +
>> +	return;
>> +
>> +err_drm_client_init:
>> +	drm_fb_helper_unprepare(fb_helper);
>> +	kfree(fb_helper);
>> +	return;
>>   }
>>   EXPORT_SYMBOL(drm_fbdev_generic_setup);
>> -- 
>> 2.39.0

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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