Re: [PATCH v4 2/2] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jan 12, 2017 at 06:42:50AM -0800, Luis R. Rodriguez wrote:
> We need to ensure that when driver developers use the custom firmware
> fallback mechanism it was not a copy and paste bug. These use cases on
> upstream drivers are rare, we only have 2 upstream users and its for
> really old drivers. Since valid uses are rare but possible enable a
> white-list for its use, and use this same white-list annotation to refer
> to the documentation covering the custom use case.
> 
> New faulty users can be reported via 0-day now.
> 
> v2: change dependencies on rules make more sense, and fixed
>     context mode
> 
> Cc: Fengguang Wu <fengguang.wu@intel.com>
> Cc: Richard Purdie <rpurdie@rpsys.net>
> Cc: Jacek Anaszewski <j.anaszewski@samsung.com>
> Cc: linux-leds@vger.kernel.org
> Cc: Abhay Salunke <Abhay_Salunke@dell.com>
> Acked-by: Jacek Anaszewski <j.anaszewski@samsung.com>
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> ---
>  Documentation/driver-api/firmware/fallback-mechanisms.rst     | 7 +++++--
>  drivers/firmware/dell_rbu.c                                   | 1 +
>  drivers/leds/leds-lp55xx-common.c                             | 1 +
>  include/linux/firmware.h                                      | 7 +++++++
>  scripts/coccinelle/api/request_firmware-custom-fallback.cocci | 9 ++++++++-
>  5 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/driver-api/firmware/fallback-mechanisms.rst b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> index b87a292153c6..73f509a8d2de 100644
> --- a/Documentation/driver-api/firmware/fallback-mechanisms.rst
> +++ b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> @@ -184,8 +184,11 @@ load firmware for you through a custom path.
>  
>  The custom fallback mechanism can often be enabled by mistake. We currently
>  have only 2 users of it, and little justification to enable it for other users.
> -Since it is a common driver developer mistake to enable it, help police for
> -new users of the custom fallback mechanism with::
> +Since it is a common driver developer mistake to enable it, driver developers
> +should use DECLARE_FW_CUSTOM_FALLBACK() to both white-list and validate their
> +use and also refer to the documentation for the custom loading solution.
> +
> +Invalid users of the custom fallback mechanism can be policed using::

Ick, no, why?  Why not just add a checkpatch rule instead?

>  
>          $ export COCCI=scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
>          $ make coccicheck MODE=report
> diff --git a/drivers/firmware/dell_rbu.c b/drivers/firmware/dell_rbu.c
> index 2f452f1f7c8a..3f2aa35bc54d 100644
> --- a/drivers/firmware/dell_rbu.c
> +++ b/drivers/firmware/dell_rbu.c
> @@ -586,6 +586,7 @@ static ssize_t read_rbu_image_type(struct file *filp, struct kobject *kobj,
>  	return size;
>  }
>  
> +DECLARE_FW_CUSTOM_FALLBACK("Documentation/dell_rbu.txt");

That's a pain.

>  static ssize_t write_rbu_image_type(struct file *filp, struct kobject *kobj,
>  				    struct bin_attribute *bin_attr,
>  				    char *buffer, loff_t pos, size_t count)
> diff --git a/drivers/leds/leds-lp55xx-common.c b/drivers/leds/leds-lp55xx-common.c
> index 5377f22ff994..04161428ee3b 100644
> --- a/drivers/leds/leds-lp55xx-common.c
> +++ b/drivers/leds/leds-lp55xx-common.c
> @@ -219,6 +219,7 @@ static void lp55xx_firmware_loaded(const struct firmware *fw, void *context)
>  	release_firmware(chip->fw);
>  }
>  
> +DECLARE_FW_CUSTOM_FALLBACK("Documentation/leds/leds-lp55xx.txt");

Same here.

>  static int lp55xx_request_firmware(struct lp55xx_chip *chip)
>  {
>  	const char *name = chip->cl->name;
> diff --git a/include/linux/firmware.h b/include/linux/firmware.h
> index b1f9f0ccb8ac..e6ca19c03dcc 100644
> --- a/include/linux/firmware.h
> +++ b/include/linux/firmware.h
> @@ -8,6 +8,13 @@
>  #define FW_ACTION_NOHOTPLUG 0
>  #define FW_ACTION_HOTPLUG 1
>  
> +/*
> + * Helper for scripts/coccinelle/api/request_firmware-custom-fallback.cocci
> + * and so users can also easily search for the documentation for the
> + * respectively needed custom fallback mechanism.
> + */
> +#define DECLARE_FW_CUSTOM_FALLBACK(__usermode_helper)

So you really don't need to put anything "valid" in the define argument?
This feels like such a horrid hack, I really don't like it, especially
as we don't do it anywhere else in the kernel, right?  Why start now?

thanks,

greg k-h