linux-kernel - Re: [PATCH v2] drm: Improve the output_poll

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Message-ID: <YAGhRz0ac6GDBFDI@phenom.ffwll.local>
Date:   Fri, 15 Jan 2021 15:05:59 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     "ZhiJie.Zhang" <zhangzhijie@...ngson.cn>
Cc:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: Improve the output_poll_changed description

On Fri, Jan 15, 2021 at 11:33:28AM +0800, ZhiJie.Zhang wrote:
> From: zhangzhijie <zhangzhijie@...ngson.cn>
> 
> this callback was used by drm_kms_helper_hotplug_event()
> 
> V2: (Thanks for Daniel's suggestions)
> - remove the FIXME below.since with the drm_client
> - infrastructure and the generic fbdev emulation we've
> - resolved this all very neatly now.
> 
> Signed-off-by: zhangzhijie <zhangzhijie@...ngson.cn>
> Signed-off-by: ZhiJie.Zhang <zhangzhijie@...ngson.cn>
> ---
>  include/drm/drm_mode_config.h | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index ab424ddd7665..50541980f7f2 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -104,13 +104,8 @@ struct drm_mode_config_funcs {
>  	 * changes.
>  	 *
>  	 * Drivers implementing fbdev emulation with the helpers can call
> -	 * drm_fb_helper_hotplug_changed from this hook to inform the fbdev
> +	 * drm_kms_helper_hotplug_event() from this hook to inform the fbdev

Hm I looked at this again, and this change is actually wrong. Both
functions exists, but calling drm_kms_helper_hotplug_event() from this hook
would result in an endless loop until we crash somewhere.

>  	 * helper of output changes.

Ah I meant not just removing this, but explaining what to do now instead.
Suggestion:

	 * This hook is deprecated, drivers should instead use
	 * drm_fbdev_generic_setup() which takes care of any necessary
	 * hotplug event forwarding already without further involvement by
	 * the driver.

Can you pls respin, with the function change dropped and the fixme
replaced with the above?

Thanks, Daniel


> -	 *
> -	 * FIXME:
> -	 *
> -	 * Except that there's no vtable for device-level helper callbacks
> -	 * there's no reason this is a core function.
>  	 */
>  	void (*output_poll_changed)(struct drm_device *dev);
>  
> -- 
> 2.29.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch