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

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:

quoted

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

quoted

@@ -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