linux-kernel - Re: [PATCH] firmware loader: allow disabling of udev as firmware loader

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Message-ID: <CAG-2HqW1_=wCz0wjP92L7Of18HO_30Aboa4wKUuYWr+k+NryuA@mail.gmail.com>
Date:	Wed, 4 Jun 2014 16:34:51 +0200
From:	Tom Gundersen <teg@...m.no>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Abhay Salunke <Abhay_Salunke@...l.com>,
	Stefan Roese <sr@...x.de>, Arnd Bergmann <arnd@...db.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [PATCH] firmware loader: allow disabling of udev as firmware loader

On Wed, Jun 4, 2014 at 4:20 PM, Takashi Iwai <tiwai@...e.de> wrote:
> At Mon,  2 Jun 2014 20:24:34 +0200,
> Tom Gundersen wrote:
>>
>> Currently (at least) the dell-rbu driver selects FW_LOADER_USER_HELPER,
>> which means that distros can't really stop loading firmware through udev
>> without breaking other users (though some have).
>>
>> Ideally we would remove/disable the udev firmware helper in both the kernel
>> and in udev, but if we were to disable it in udev and not the kernel, the result
>> would be (seemingly) hung kernels as no one would be around to cancel firmware
>> requests.
>>
>> This patch allows udev firmware loading to be disabled while still allowing
>> non-udev firmware loading, as done by the dell-rbu driver, to continue
>> working. This is achieved by only using the fallback mechanism when the
>> uevent is suppressed.
>>
>> Tested with
>>     FW_LOADER_USER_HELPER=n
>>     LATTICE_ECP3_CONFIG=y
>>     DELL_RBU=y
>> and udev without the firmware loading support, but I don't have the hardware
>> to test the lattice/dell drivers, so additional testing would be appreciated.
>
> The logic of this patch looks good to me, but the Kconfig items become
> confusing by this.  Basically what we'd need is a Kconfig item
> deciding whether to build the user helper or not, in addition to a
> Kconfig item for deciding the fallback mode of request_firmware().
>
> What about the patch like below instead?  It's smaller and the meaning
> of Kconfig items are clearer.  (In the final form, the help text
> change you added should be included there, too.)

Yeah, this way is clearer, so looks good to me.

Reviewed-by: Tom Gundersen <teg@...m.no>

> The only (and biggest) drawback is, however, that the user-selectable
> Kconfig would be actually renamed from CONFIG_FW_LOADER_USER_HELPER to
> CONFIG_FW_LOADER_USER_HELPER_FALLBACK.

I also first intended to rename the Kconfig stuff in this way, but I
thought prompting the user was a no-no. That said, drawing attention
to the fact that people are probably better off changing this from y
to n may be a good thing in the end.

> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 8fa8deab6449..195b08f49209 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -144,8 +144,12 @@ config EXTRA_FIRMWARE_DIR
>           some other directory containing the firmware files.
>
>  config FW_LOADER_USER_HELPER
> +       bool
> +
> +config FW_LOADER_USER_HELPER_FALLBACK
>         bool "Fallback user-helper invocation for firmware loading"
>         depends on FW_LOADER
> +       select FW_LOADER_USER_HELPER
>         default y
>         help
>           This option enables / disables the invocation of user-helper
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index d276e33880be..e98fd78c5c40 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -100,9 +100,14 @@ static inline long firmware_loading_timeout(void)
>  #define FW_OPT_UEVENT  (1U << 0)
>  #define FW_OPT_NOWAIT  (1U << 1)
>  #ifdef CONFIG_FW_LOADER_USER_HELPER
> -#define FW_OPT_FALLBACK        (1U << 2)
> +#define FW_OPT_USERHELPER      (1U << 2)
>  #else
> -#define FW_OPT_FALLBACK        0
> +#define FW_OPT_USERHELPER      0
> +#endif
> +#ifdef CONFIG_FW_LOADER_USER_HELPER_FALLBACK
> +#define FW_OPT_FALLBACK                FW_OPT_USERHELPER
> +#else
> +#define FW_OPT_FALLBACK                0
>  #endif
>
>  struct firmware_cache {
> @@ -1111,7 +1116,7 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
>
>         ret = fw_get_filesystem_firmware(device, fw->priv);
>         if (ret) {
> -               if (opt_flags & FW_OPT_FALLBACK) {
> +               if (opt_flags & FW_OPT_USERHELPER) {
>                         dev_warn(device,
>                                  "Direct firmware load failed with error %d\n",
>                                  ret);
> @@ -1277,7 +1282,7 @@ request_firmware_nowait(
>         fw_work->context = context;
>         fw_work->cont = cont;
>         fw_work->opt_flags = FW_OPT_NOWAIT | FW_OPT_FALLBACK |
> -               (uevent ? FW_OPT_UEVENT : 0);
> +               (uevent ? FW_OPT_UEVENT : FW_OPT_USERHELPER);
>
>         if (!try_module_get(module)) {
>                 kfree(fw_work);
--
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