linux-kernel - Re: [RESEND RFC PATCH 2/5] firmware: sysfb: Add helpers to unregister a pdev and disable registration

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Message-ID: <Yk6plGLa+uOb0ZyJ@phenom.ffwll.local>
Date:   Thu, 7 Apr 2022 11:06:28 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Borislav Petkov <bp@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RESEND RFC PATCH 2/5] firmware: sysfb: Add helpers to
 unregister a pdev and disable registration

On Wed, Apr 06, 2022 at 11:39:16PM +0200, Javier Martinez Canillas wrote:
> These can be used by subsystems to unregister a platform device registered
> by sysfb and also to disable future platform device registration in sysfb.
> 
> Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
>  drivers/firmware/sysfb.c | 47 +++++++++++++++++++++++++++++++++++-----
>  include/linux/sysfb.h    | 19 ++++++++++++++++
>  2 files changed, 60 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
> index b032f40a92de..08ae78c083f1 100644
> --- a/drivers/firmware/sysfb.c
> +++ b/drivers/firmware/sysfb.c
> @@ -34,21 +34,52 @@
>  #include <linux/screen_info.h>
>  #include <linux/sysfb.h>
>  
> +static struct platform_device *pd;
> +static DEFINE_MUTEX(load_lock);
> +static bool disabled;
> +
> +void sysfb_disable(void)
> +{
> +	mutex_lock(&load_lock);
> +	disabled = true;
> +	mutex_unlock(&load_lock);
> +}
> +EXPORT_SYMBOL_GPL(sysfb_disable);
> +
> +bool sysfb_try_unregister(struct device *dev)
> +{
> +	bool ret = true;
> +
> +	mutex_lock(&load_lock);
> +	if (!pd || pd != to_platform_device(dev))
> +		return false;
> +
> +	platform_device_unregister(to_platform_device(dev));
> +	pd = NULL;
> +	mutex_unlock(&load_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(sysfb_try_unregister);

Kerneldoc for these plus adding that to
Documentation/firmware/other_interfaces.rst would be really neat.

With that added Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>


> +
>  static __init int sysfb_init(void)
>  {
>  	struct screen_info *si = &screen_info;
>  	struct simplefb_platform_data mode;
> -	struct platform_device *pd;
>  	const char *name;
>  	bool compatible;
> -	int ret;
> +	int ret = 0;
> +
> +	mutex_lock(&load_lock);
> +	if (disabled)
> +		goto unlock_mutex;
>  
>  	/* try to create a simple-framebuffer device */
>  	compatible = sysfb_parse_mode(si, &mode);
>  	if (compatible) {
>  		pd = sysfb_create_simplefb(si, &mode);
>  		if (!IS_ERR(pd))
> -			return 0;
> +			goto unlock_mutex;
>  	}
>  
>  	/* if the FB is incompatible, create a legacy framebuffer device */
> @@ -60,8 +91,10 @@ static __init int sysfb_init(void)
>  		name = "platform-framebuffer";
>  
>  	pd = platform_device_alloc(name, 0);
> -	if (!pd)
> -		return -ENOMEM;
> +	if (!pd) {
> +		ret = -ENOMEM;
> +		goto unlock_mutex;
> +	}
>  
>  	sysfb_apply_efi_quirks(pd);
>  
> @@ -73,9 +106,11 @@ static __init int sysfb_init(void)
>  	if (ret)
>  		goto err;
>  
> -	return 0;
> +	goto unlock_mutex;
>  err:
>  	platform_device_put(pd);
> +unlock_mutex:
> +	mutex_unlock(&load_lock);
>  	return ret;
>  }
>  
> diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
> index 708152e9037b..e8c0313fac8f 100644
> --- a/include/linux/sysfb.h
> +++ b/include/linux/sysfb.h
> @@ -55,6 +55,25 @@ struct efifb_dmi_info {
>  	int flags;
>  };
>  
> +#ifdef CONFIG_SYSFB
> +
> +void sysfb_disable(void);
> +bool sysfb_try_unregister(struct device *dev);
> +
> +#else /* CONFIG_SYSFB */
> +
> +static inline void sysfb_disable(void)
> +{
> +
> +}
> +
> +static inline bool sysfb_try_unregister(struct device *dev)
> +{
> +	return false;
> +}
> +
> +#endif /* CONFIG_SYSFB */
> +
>  #ifdef CONFIG_EFI
>  
>  extern struct efifb_dmi_info efifb_dmi_list[];
> -- 
> 2.35.1
> 

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