Re: [PATCH v5 2/7] firmware: sysfb: Add helpers to unregister a pdev and disable registration

[Thomas Zimmermann <tzimmermann@suse.de>]

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Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
> 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@ffwll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
> 
> (no changes since v4)
> 
> Changes in v4:
> - Make sysfb_disable() to also attempt to unregister a device.
> 
> Changes in v2:
> - Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).
> 
>   .../driver-api/firmware/other_interfaces.rst  |  6 ++
>   drivers/firmware/sysfb.c                      | 87 +++++++++++++++++--
>   include/linux/sysfb.h                         | 19 ++++
>   3 files changed, 106 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
> index b81794e0cfbb..06ac89adaafb 100644
> --- a/Documentation/driver-api/firmware/other_interfaces.rst
> +++ b/Documentation/driver-api/firmware/other_interfaces.rst
> @@ -13,6 +13,12 @@ EDD Interfaces
>   .. kernel-doc:: drivers/firmware/edd.c
>      :internal:
>   
> +Generic System Framebuffers Interface
> +-------------------------------------
> +
> +.. kernel-doc:: drivers/firmware/sysfb.c
> +   :export:
> +
>   Intel Stratix10 SoC Service Layer
>   ---------------------------------
>   Some features of the Intel Stratix10 SoC require a level of privilege
> diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
> index b032f40a92de..6768968949e6 100644
> --- a/drivers/firmware/sysfb.c
> +++ b/drivers/firmware/sysfb.c
> @@ -34,21 +34,92 @@
>   #include <linux/screen_info.h>
>   #include <linux/sysfb.h>
>   
> +static struct platform_device *pd;
> +static DEFINE_MUTEX(disable_lock);
> +static bool disabled;
> +
> +static bool sysfb_unregister(void)
> +{
> +	if (IS_ERR_OR_NULL(pd))
> +		return false;
> +
> +	platform_device_unregister(pd);
> +	pd = NULL;
> +
> +	return true;
> +}
> +
> +/**
> + * sysfb_disable() - disable the Generic System Framebuffers support
> + *
> + * This disables the registration of system framebuffer devices that match the
> + * generic drivers that make use of the system framebuffer set up by firmware.
> + *
> + * It also unregisters a device if this was already registered by sysfb_init().

Why? I still cannot wrap my mind around, why we need to store *pd at all 
and use sysfb_try_unregister() for unregistering.

> + *
> + * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
> + *          against sysfb_init(), that registers a system framebuffer device and
> + *          sysfb_try_unregister(), that tries to unregister a framebuffer device.
> + */
> +void sysfb_disable(void)
> +{
> +	mutex_lock(&disable_lock);
> +	sysfb_unregister();
> +	disabled = true;
> +	mutex_unlock(&disable_lock);
> +}
> +EXPORT_SYMBOL_GPL(sysfb_disable);
> +
> +/**
> + * sysfb_try_unregister() - attempt to unregister a system framebuffer device
> + * @dev: device to unregister
> + *
> + * This tries to unregister a system framebuffer device if this was registered
> + * by the Generic System Framebuffers. The device will only be unregistered if
> + * it was registered by sysfb_init(), otherwise it will not be unregistered.
> + *
> + * Context: The function can sleep. a @load_lock mutex is acquired to serialize
> + *          against sysfb_init(), that registers a simple framebuffer device and
> + *          sysfb_disable(), that disables the Generic System Framebuffers support.
> + *
> + * Return:
> + * * true          - the device was unregistered successfully
> + * * false         - the device was not unregistered
> + */
> +bool sysfb_try_unregister(struct device *dev)

As it stands, I strongly object the use of this function as still don't 
really get the purpose. It looks like a glorified wrapper around 
platform_device_unregister(). Do we need disable_lock to serialize with 
something else?

Best regards
Thomas


> +{
> +	bool ret = false;
> +
> +	mutex_lock(&disable_lock);
> +	if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev))
> +		goto unlock_mutex;
> +
> +	ret = sysfb_unregister();
> +
> +unlock_mutex:
> +	mutex_unlock(&disable_lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(sysfb_try_unregister);
> +
>   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(&disable_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 +131,10 @@ 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 +146,11 @@ static __init int sysfb_init(void)
>   	if (ret)
>   		goto err;
>   
> -	return 0;
> +	goto unlock_mutex;
>   err:
>   	platform_device_put(pd);
> +unlock_mutex:
> +	mutex_unlock(&disable_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[];

-- 
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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