[PATCH v3 2/5] firmware: annotate thou shalt not request fw on init or probe

[Gabriel Paubert]

On Tue, Aug 23, 2016 at 05:45:04PM -0700, mcgrof at kernel.org wrote:

[snip]
> ---
>  Documentation/firmware_class/README                |  20 ++++
>  drivers/base/Kconfig                               |   2 +-
>  .../request_firmware-avoid-init-probe-init.cocci   | 130 +++++++++++++++++++++
>  3 files changed, 151 insertions(+), 1 deletion(-)
>  create mode 100644 scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> 
> diff --git a/Documentation/firmware_class/README b/Documentation/firmware_class/README
> index cafdca8b3b15..056d1cb9d365 100644
> --- a/Documentation/firmware_class/README
> +++ b/Documentation/firmware_class/README
> @@ -93,6 +93,26 @@
>     user contexts to request firmware asynchronously, but can't be called
>     in atomic contexts.
>  
> +Requirements:
> +=============
> +
> +You should avoid at all costs requesting firmware on both init and probe paths
> +of your device driver. Reason for this is the complexity needed to ensure a
> +firmware will be available for a driver early in boot through different
> +build configurations. Consider built-in drivers needing firmware early, or
> +consider a driver assuming it will only get firmware after pivot_root().
> +
> +Drivers that really need firmware early should use stuff the firmware in

Minor grammatical nit: s/use//

> +initramfs or consider using CONFIG_EXTRA_FIRMWARE. Using initramfs is much
> +more portable to more distributions as not all distributions wish to enable
> +CONFIG_EXTRA_FIRMWARE. Should a driver require the firmware being built-in
> +it should depend on CONFIG_EXTRA_FIRMWARE. There is no current annotation for
> +requiring a firmware on initramfs.
> +
> +If you're a maintainer you can help police this with:
> +
> +$ export COCCI=scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> +$ make coccicheck MODE=report
>  
>   about in-kernel persistence:
>   ---------------------------