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Date: Mon, 25 Apr 2022 10:24:23 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Javier Martinez Canillas <javierm@...hat.com>,
linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Daniel Vetter <daniel.vetter@...ll.ch>,
dri-devel@...ts.freedesktop.org, Borislav Petkov <bp@...e.de>,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 2/5] firmware: sysfb: Add helpers to unregister a pdev
and disable registration
Hi
Am 20.04.22 um 10:53 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@...ll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> ---
>
> (no changes since v2)
>
> 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 | 73 +++++++++++++++++--
> include/linux/sysfb.h | 19 +++++
> 3 files changed, 92 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..a50d2858ce4d 100644
> --- a/drivers/firmware/sysfb.c
> +++ b/drivers/firmware/sysfb.c
> @@ -34,21 +34,78 @@
> #include <linux/screen_info.h>
> #include <linux/sysfb.h>
>
> +static struct platform_device *pd;
You could have multiple instances of simple-framebuffer because you
don't know what the firmware set up. It originated from DT and EFI/VESA
is really just an afterthought. If there is more than 1 instance, your
entire unregistering breaks down.
(I've been told that such multi-output cases exist in the context of OF
framebuffers. Something similar could exist for simple-frambuffer as well.)
Best regards
Thomas
> +static DEFINE_MUTEX(load_lock);
> +static bool disabled;
> +
> +/**
> + * 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.
> + *
> + * Context: The function can sleep. A @load_lock mutex is acquired to serialize
> + * against sysfb_init(), that registers a system framebuffer device and
> + * sysfb_try_unregister(), that tries to unregister framebuffer devices.
> + */
> +void sysfb_disable(void)
> +{
> + mutex_lock(&load_lock);
> + disabled = true;
> + mutex_unlock(&load_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)
> +{
> + 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);
> +
> 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 +117,10 @@ 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 +132,11 @@ 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[];
--
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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