diff mbox

[v6,05/13] firmware_loader: enhance Kconfig documentation over FW_LOADER

Message ID 20180508181247.19431-6-mcgrof@kernel.org
State New, archived
Headers show

Commit Message

Luis Chamberlain May 8, 2018, 6:12 p.m. UTC
If you try to read FW_LOADER today it speaks of old riddles and
unless you have been following development closely you will loose
track of what is what. Even the documentation for PREVENT_FIRMWARE_BUILD
is a bit fuzzy and how it fits into this big picture.

Give the FW_LOADER kconfig documentation some love with more up to
date developments and recommendations. While at it, wrap the FW_LOADER
code into its own menu to compartamentalize and make it clearer which
components really are part of the FW_LOADER. This should also make
it easier to later move these kconfig entries into the firmware_loader/
directory later.

This also now recommends using firmwared [0] for folks left needing a uevent
handler in userspace for the sysfs firmware fallback mechanis given udev's
uevent firmware mechanism was ripped out a while ago.

[0] https://github.com/teg/firmwared

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
 drivers/base/Kconfig | 165 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 131 insertions(+), 34 deletions(-)

Comments

Kees Cook May 8, 2018, 10:42 p.m. UTC | #1
On Tue, May 8, 2018 at 11:12 AM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> If you try to read FW_LOADER today it speaks of old riddles and
> unless you have been following development closely you will loose

Typo: lose

> track of what is what. Even the documentation for PREVENT_FIRMWARE_BUILD
> is a bit fuzzy and how it fits into this big picture.
>
> Give the FW_LOADER kconfig documentation some love with more up to
> date developments and recommendations. While at it, wrap the FW_LOADER
> code into its own menu to compartamentalize and make it clearer which

Typo: compartmentalize

> components really are part of the FW_LOADER. This should also make
> it easier to later move these kconfig entries into the firmware_loader/
> directory later.
>
> This also now recommends using firmwared [0] for folks left needing a uevent
> handler in userspace for the sysfs firmware fallback mechanis given udev's
> uevent firmware mechanism was ripped out a while ago.
>
> [0] https://github.com/teg/firmwared
>
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> ---
>  drivers/base/Kconfig | 165 ++++++++++++++++++++++++++++++++++---------
>  1 file changed, 131 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 29b0eb452b3a..a4fe86caecca 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -70,39 +70,64 @@ config STANDALONE
>           If unsure, say Y.
>
>  config PREVENT_FIRMWARE_BUILD
> -       bool "Prevent firmware from being built"
> +       bool "Disable drivers features which enable custom firmware building"
>         default y
>         help
> -         Say yes to avoid building firmware. Firmware is usually shipped
> -         with the driver and only when updating the firmware should a
> -         rebuild be made.
> -         If unsure, say Y here.
> +         Say yes to disable driver features which enable building a custom
> +         driver firmwar at kernel build time. These drivers do not use the

Typo: firmware

> +         kernel firmware API to load firmware (CONFIG_FW_LOADER), instead they
> +         use their own custom loading mechanism. The required firmware is
> +         usually shipped with the driver, building the driver firmware
> +         should only be needed if you have an updated firmware source.
> +
> +         Firmware should not be being built as part of kernel, these days
> +         you should always prevent this and say Y here. There are only two
> +         old drivers which enable building of its firmware at kernel build
> +         time:
> +
> +           o CONFIG_WANXL through CONFIG_WANXL_BUILD_FIRMWARE
> +           o CONFIG_SCSI_AIC79XX through CONFIG_AIC79XX_BUILD_FIRMWARE
> +
> +menu "Firmware loader"
>
>  config FW_LOADER
> -       tristate "Userspace firmware loading support" if EXPERT
> +       tristate "Firmware loading facility" if EXPERT
>         default y
>         ---help---
> -         This option is provided for the case where none of the in-tree modules
> -         require userspace firmware loading support, but a module built
> -         out-of-tree does.
> +         This enables the firmware loading facility in the kernel. The kernel
> +         will first look for built-in firmware, if it has any. Next, it will
> +         look for the requested firmware in a series of filesystem paths:
> +
> +               o firmware_class path module parameter or kernel boot param
> +               o /lib/firmware/updates/UTS_RELEASE
> +               o /lib/firmware/updates
> +               o /lib/firmware/UTS_RELEASE
> +               o /lib/firmware
> +
> +         Enabling this feature only increases your kernel image by about
> +         828 bytes, enable this option unless you are certain you don't
> +         need firmware.
> +
> +         You typically want this built-in (=y) but you can also enable this
> +         as a module, in which case the firmware_class module will be built.
> +         You also want to be sure to enable this built-in if you are going to
> +         enable built-in firmware (CONFIG_EXTRA_FIRMWARE).
> +
> +if FW_LOADER
>
>  config EXTRA_FIRMWARE
> -       string "External firmware blobs to build into the kernel binary"
> -       depends on FW_LOADER
> +       string "Build these firmware blobs into the kernel binary"

Maybe "Build named firmware blobs ..." "these" took me a while to figure out.

>         help
> -         Various drivers in the kernel source tree may require firmware,
> -         which is generally available in your distribution's linux-firmware
> -         package.
> +         Device drivers which require firmware can typically deal with
> +         having the kernel load firmware from the various supported
> +         /lib/firmware/ paths. This option enables you to build into the
> +         kernel firmware files. Built-in firmware searches are preceeded

Typo: preceded

> +         over firmware lookups using your filesystem over the supported
> +         /lib/firmware paths documented on CONFIG_FW_LOADER.
>
> -         The linux-firmware package should install firmware into
> -         /lib/firmware/ on your system, so they can be loaded by userspace
> -         helpers on request.
> -
> -         This option allows firmware to be built into the kernel for the case
> -         where the user either cannot or doesn't want to provide it from
> -         userspace at runtime (for example, when the firmware in question is
> -         required for accessing the boot device, and the user doesn't want to
> -         use an initrd).
> +         This may be useful for testing or if the firmware is required early on
> +         in boot and cannot rely on the firmware being placed in an initrd or
> +         initramfs.
>
>           This option is a string and takes the (space-separated) names of the
>           firmware files -- the same names that appear in MODULE_FIRMWARE()
> @@ -113,7 +138,7 @@ config EXTRA_FIRMWARE
>           For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
>           the usb8388.bin file into /lib/firmware, and build the kernel. Then
>           any request_firmware("usb8388.bin") will be satisfied internally
> -         without needing to call out to userspace.
> +         inside the kernel without ever looking at your filesystem at runtime.
>
>           WARNING: If you include additional firmware files into your binary
>           kernel image that are not available under the terms of the GPL,
> @@ -130,22 +155,94 @@ config EXTRA_FIRMWARE_DIR
>           looks for the firmware files listed in the EXTRA_FIRMWARE option.
>
>  config FW_LOADER_USER_HELPER
> -       bool
> +       bool "Enable the firmware sysfs fallback mechanism"
> +       help
> +         This option enables a sysfs loading facility to enable firmware
> +         loading to the kernel through userspace as a fallback mechanism
> +         if and only if the kernel's direct filesystem lookup for the
> +         firmware failed using the different /lib/firmware/ paths, or the
> +         path specified in the firmware_class path module parameter, or the
> +         firmware_class path kernel boot parameter if the firmware_class is
> +         built-in. For details on how to work with the sysfs fallback mechanism
> +         refer to Documentation/driver-api/firmware/fallback-mechanisms.rst.
> +
> +         The direct filesystem lookup for firwmare is always used first now.

Typo: firmware

> +
> +         If the kernel's direct filesystem lookup for firware fails to find
> +         the requested firmware a sysfs fallback loading facility is made
> +         available and userspace is informed about this through uevents.
> +         The uevent can be supressed if the driver explicitly requested it,
> +         this is known as the driver using the custom fallback mechanism.
> +         If the custom fallback mechanism is used userspace must always
> +         acknowledge failure to find firmware as the timeout for the fallback
> +         mechanism is disabled, and failed requests will linger forever.
> +
> +         This used to be the default firmware loading facility, and udev used
> +         to listen for uvents to load firmware for the kernel. The firmware
> +         loading facility functionality in udev has been removed, as such it
> +         can no longer be relied upon as a fallback mechanism. Linux no longer
> +         relies on or uses a fallback mechanism in userspace. If you need to
> +         rely on one refer to the permissively licensed firmwared:

Typo: firmware

> +
> +         https://github.com/teg/firmwared
> +
> +         Since this was the default firmware loading facility at one point,
> +         old userspace may exist which relies upon it, and as such this
> +         mechanism can never be removed from the kernel.
> +
> +         You should only enable this functionality if you are certain you
> +         require a fallback mechanism and have a userspace mechanism ready to
> +         load firmware in case it is not found. One main reason for this may
> +         be if you have drivers which require firmware built-in and for
> +         whatever reason cannot place the required firmware in initramfs.
> +         Another reason kernels may have this feature enabled is to support a
> +         driver which explicitly relies on this fallback mechanism. Only two
> +         drivers need this today:
> +
> +           o CONFIG_LEDS_LP55XX_COMMON
> +           o CONFIG_DELL_RBU
> +
> +         Outside of supporting the above drivers, another reason for needing
> +         this may be that your firmware resides outside of the paths the kernel
> +         looks for and cannot possibily be specified using the firmware_class
> +         path module parameter or kernel firmware_class path boot parameter
> +         if firmware_class is built-in.
> +
> +         A modern use case may be to temporarily mount a custom partition
> +         during provisioning which is only accessible to userspace, and then
> +         to use it to look for and fetch the required firmware. Such type of
> +         driver functionality may not even ever be desirable upstream by
> +         vendors, and as such is only required to be supported as an interface
> +         for provisioning. Since udev's firmware loading facility has been
> +         removed you can use firmwared or a fork of it to customize how you
> +         want to load firmware based on uevents issued.
> +
> +         Enabling this option will increase your kernel image size by about
> +         13436 bytes.
> +
> +         If you are unsure about this, say N here, unless you are Linux
> +         distribution and need to support the above two drivers, or you are
> +         certain you need to support some really custom firmware loading
> +         facility in userspace.
>
>  config FW_LOADER_USER_HELPER_FALLBACK
> -       bool "Fallback user-helper invocation for firmware loading"
> -       depends on FW_LOADER
> -       select FW_LOADER_USER_HELPER
> +       bool "Force the firmware sysfs fallback mechanism when possible"
> +       depends on FW_LOADER_USER_HELPER
>         help
> -         This option enables / disables the invocation of user-helper
> -         (e.g. udev) for loading firmware files as a fallback after the
> -         direct file loading in kernel fails.  The user-mode helper is
> -         no longer required unless you have a special firmware file that
> -         resides in a non-standard path. Moreover, the udev support has
> -         been deprecated upstream.
> +         Enabling this option forces a sysfs userspace fallback mechanism
> +         to be used for all firmware requests which explicitly do not disable a
> +         a fallback mechanism. Firmware calls which do prohibit a fallback
> +         mechanism is request_firmware_direct(). This option is kept for
> +          backward compatibility purposes given this precise mechanism can also
> +         be enabled by setting the proc sysctl value to true:
> +
> +              /proc/sys/kernel/firmware_config/force_sysfs_fallback
>
>           If you are unsure about this, say N here.
>
> +endif # FW_LOADER
> +endmenu
> +
>  config WANT_DEV_COREDUMP
>         bool
>         help
> --
> 2.17.0
>


-Kees
Luis Chamberlain May 9, 2018, 8:55 p.m. UTC | #2
On Tue, May 08, 2018 at 03:42:33PM -0700, Kees Cook wrote:
> On Tue, May 8, 2018 at 11:12 AM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> > +         This used to be the default firmware loading facility, and udev used
> > +         to listen for uvents to load firmware for the kernel. The firmware
> > +         loading facility functionality in udev has been removed, as such it
> > +         can no longer be relied upon as a fallback mechanism. Linux no longer
> > +         relies on or uses a fallback mechanism in userspace. If you need to
> > +         rely on one refer to the permissively licensed firmwared:
> 
> Typo: firmware

Thanks fixed all typos except this one, this one is meant to be firmwared as
that is the name of the project, the url is below.

> 
> > +
> > +         https://github.com/teg/firmwared

  Luis
Kees Cook May 9, 2018, 11:01 p.m. UTC | #3
On Wed, May 9, 2018 at 1:55 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> On Tue, May 08, 2018 at 03:42:33PM -0700, Kees Cook wrote:
>> On Tue, May 8, 2018 at 11:12 AM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
>> > +         This used to be the default firmware loading facility, and udev used
>> > +         to listen for uvents to load firmware for the kernel. The firmware
>> > +         loading facility functionality in udev has been removed, as such it
>> > +         can no longer be relied upon as a fallback mechanism. Linux no longer
>> > +         relies on or uses a fallback mechanism in userspace. If you need to
>> > +         rely on one refer to the permissively licensed firmwared:
>>
>> Typo: firmware
>
> Thanks fixed all typos except this one, this one is meant to be firmwared as
> that is the name of the project, the url is below.
>
>>
>> > +
>> > +         https://github.com/teg/firmwared

Oh! Yes, hah. :) Thanks!

-Kees
diff mbox

Patch

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 29b0eb452b3a..a4fe86caecca 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -70,39 +70,64 @@  config STANDALONE
 	  If unsure, say Y.
 
 config PREVENT_FIRMWARE_BUILD
-	bool "Prevent firmware from being built"
+	bool "Disable drivers features which enable custom firmware building"
 	default y
 	help
-	  Say yes to avoid building firmware. Firmware is usually shipped
-	  with the driver and only when updating the firmware should a
-	  rebuild be made.
-	  If unsure, say Y here.
+	  Say yes to disable driver features which enable building a custom
+	  driver firmwar at kernel build time. These drivers do not use the
+	  kernel firmware API to load firmware (CONFIG_FW_LOADER), instead they
+	  use their own custom loading mechanism. The required firmware is
+	  usually shipped with the driver, building the driver firmware
+	  should only be needed if you have an updated firmware source.
+
+	  Firmware should not be being built as part of kernel, these days
+	  you should always prevent this and say Y here. There are only two
+	  old drivers which enable building of its firmware at kernel build
+	  time:
+
+	    o CONFIG_WANXL through CONFIG_WANXL_BUILD_FIRMWARE
+	    o CONFIG_SCSI_AIC79XX through CONFIG_AIC79XX_BUILD_FIRMWARE
+
+menu "Firmware loader"
 
 config FW_LOADER
-	tristate "Userspace firmware loading support" if EXPERT
+	tristate "Firmware loading facility" if EXPERT
 	default y
 	---help---
-	  This option is provided for the case where none of the in-tree modules
-	  require userspace firmware loading support, but a module built
-	  out-of-tree does.
+	  This enables the firmware loading facility in the kernel. The kernel
+	  will first look for built-in firmware, if it has any. Next, it will
+	  look for the requested firmware in a series of filesystem paths:
+
+		o firmware_class path module parameter or kernel boot param
+		o /lib/firmware/updates/UTS_RELEASE
+		o /lib/firmware/updates
+		o /lib/firmware/UTS_RELEASE
+		o /lib/firmware
+
+	  Enabling this feature only increases your kernel image by about
+	  828 bytes, enable this option unless you are certain you don't
+	  need firmware.
+
+	  You typically want this built-in (=y) but you can also enable this
+	  as a module, in which case the firmware_class module will be built.
+	  You also want to be sure to enable this built-in if you are going to
+	  enable built-in firmware (CONFIG_EXTRA_FIRMWARE).
+
+if FW_LOADER
 
 config EXTRA_FIRMWARE
-	string "External firmware blobs to build into the kernel binary"
-	depends on FW_LOADER
+	string "Build these firmware blobs into the kernel binary"
 	help
-	  Various drivers in the kernel source tree may require firmware,
-	  which is generally available in your distribution's linux-firmware
-	  package.
+	  Device drivers which require firmware can typically deal with
+	  having the kernel load firmware from the various supported
+	  /lib/firmware/ paths. This option enables you to build into the
+	  kernel firmware files. Built-in firmware searches are preceeded
+	  over firmware lookups using your filesystem over the supported
+	  /lib/firmware paths documented on CONFIG_FW_LOADER.
 
-	  The linux-firmware package should install firmware into
-	  /lib/firmware/ on your system, so they can be loaded by userspace
-	  helpers on request.
-
-	  This option allows firmware to be built into the kernel for the case
-	  where the user either cannot or doesn't want to provide it from
-	  userspace at runtime (for example, when the firmware in question is
-	  required for accessing the boot device, and the user doesn't want to
-	  use an initrd).
+	  This may be useful for testing or if the firmware is required early on
+	  in boot and cannot rely on the firmware being placed in an initrd or
+	  initramfs.
 
 	  This option is a string and takes the (space-separated) names of the
 	  firmware files -- the same names that appear in MODULE_FIRMWARE()
@@ -113,7 +138,7 @@  config EXTRA_FIRMWARE
 	  For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
 	  the usb8388.bin file into /lib/firmware, and build the kernel. Then
 	  any request_firmware("usb8388.bin") will be satisfied internally
-	  without needing to call out to userspace.
+	  inside the kernel without ever looking at your filesystem at runtime.
 
 	  WARNING: If you include additional firmware files into your binary
 	  kernel image that are not available under the terms of the GPL,
@@ -130,22 +155,94 @@  config EXTRA_FIRMWARE_DIR
 	  looks for the firmware files listed in the EXTRA_FIRMWARE option.
 
 config FW_LOADER_USER_HELPER
-	bool
+	bool "Enable the firmware sysfs fallback mechanism"
+	help
+	  This option enables a sysfs loading facility to enable firmware
+	  loading to the kernel through userspace as a fallback mechanism
+	  if and only if the kernel's direct filesystem lookup for the
+	  firmware failed using the different /lib/firmware/ paths, or the
+	  path specified in the firmware_class path module parameter, or the
+	  firmware_class path kernel boot parameter if the firmware_class is
+	  built-in. For details on how to work with the sysfs fallback mechanism
+	  refer to Documentation/driver-api/firmware/fallback-mechanisms.rst.
+
+	  The direct filesystem lookup for firwmare is always used first now.
+
+	  If the kernel's direct filesystem lookup for firware fails to find
+	  the requested firmware a sysfs fallback loading facility is made
+	  available and userspace is informed about this through uevents.
+	  The uevent can be supressed if the driver explicitly requested it,
+	  this is known as the driver using the custom fallback mechanism.
+	  If the custom fallback mechanism is used userspace must always
+	  acknowledge failure to find firmware as the timeout for the fallback
+	  mechanism is disabled, and failed requests will linger forever.
+
+	  This used to be the default firmware loading facility, and udev used
+	  to listen for uvents to load firmware for the kernel. The firmware
+	  loading facility functionality in udev has been removed, as such it
+	  can no longer be relied upon as a fallback mechanism. Linux no longer
+	  relies on or uses a fallback mechanism in userspace. If you need to
+	  rely on one refer to the permissively licensed firmwared:
+
+	  https://github.com/teg/firmwared
+
+	  Since this was the default firmware loading facility at one point,
+	  old userspace may exist which relies upon it, and as such this
+	  mechanism can never be removed from the kernel.
+
+	  You should only enable this functionality if you are certain you
+	  require a fallback mechanism and have a userspace mechanism ready to
+	  load firmware in case it is not found. One main reason for this may
+	  be if you have drivers which require firmware built-in and for
+	  whatever reason cannot place the required firmware in initramfs.
+	  Another reason kernels may have this feature enabled is to support a
+	  driver which explicitly relies on this fallback mechanism. Only two
+	  drivers need this today:
+
+	    o CONFIG_LEDS_LP55XX_COMMON
+	    o CONFIG_DELL_RBU
+
+	  Outside of supporting the above drivers, another reason for needing
+	  this may be that your firmware resides outside of the paths the kernel
+	  looks for and cannot possibily be specified using the firmware_class
+	  path module parameter or kernel firmware_class path boot parameter
+	  if firmware_class is built-in.
+
+	  A modern use case may be to temporarily mount a custom partition
+	  during provisioning which is only accessible to userspace, and then
+	  to use it to look for and fetch the required firmware. Such type of
+	  driver functionality may not even ever be desirable upstream by
+	  vendors, and as such is only required to be supported as an interface
+	  for provisioning. Since udev's firmware loading facility has been
+	  removed you can use firmwared or a fork of it to customize how you
+	  want to load firmware based on uevents issued.
+
+	  Enabling this option will increase your kernel image size by about
+	  13436 bytes.
+
+	  If you are unsure about this, say N here, unless you are Linux
+	  distribution and need to support the above two drivers, or you are
+	  certain you need to support some really custom firmware loading
+	  facility in userspace.
 
 config FW_LOADER_USER_HELPER_FALLBACK
-	bool "Fallback user-helper invocation for firmware loading"
-	depends on FW_LOADER
-	select FW_LOADER_USER_HELPER
+	bool "Force the firmware sysfs fallback mechanism when possible"
+	depends on FW_LOADER_USER_HELPER
 	help
-	  This option enables / disables the invocation of user-helper
-	  (e.g. udev) for loading firmware files as a fallback after the
-	  direct file loading in kernel fails.  The user-mode helper is
-	  no longer required unless you have a special firmware file that
-	  resides in a non-standard path. Moreover, the udev support has
-	  been deprecated upstream.
+	  Enabling this option forces a sysfs userspace fallback mechanism
+	  to be used for all firmware requests which explicitly do not disable a
+	  a fallback mechanism. Firmware calls which do prohibit a fallback
+	  mechanism is request_firmware_direct(). This option is kept for
+          backward compatibility purposes given this precise mechanism can also
+	  be enabled by setting the proc sysctl value to true:
+
+	       /proc/sys/kernel/firmware_config/force_sysfs_fallback
 
 	  If you are unsure about this, say N here.
 
+endif # FW_LOADER
+endmenu
+
 config WANT_DEV_COREDUMP
 	bool
 	help