mirror of
https://github.com/torvalds/linux
synced 2024-11-05 18:23:50 +00:00
b1425189d0
This is a tiny clean up for typos in the firmware_class README. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
128 lines
4.5 KiB
Text
128 lines
4.5 KiB
Text
|
|
request_firmware() hotplug interface:
|
|
------------------------------------
|
|
Copyright (C) 2003 Manuel Estrada Sainz
|
|
|
|
Why:
|
|
---
|
|
|
|
Today, the most extended way to use firmware in the Linux kernel is linking
|
|
it statically in a header file. Which has political and technical issues:
|
|
|
|
1) Some firmware is not legal to redistribute.
|
|
2) The firmware occupies memory permanently, even though it often is just
|
|
used once.
|
|
3) Some people, like the Debian crowd, don't consider some firmware free
|
|
enough and remove entire drivers (e.g.: keyspan).
|
|
|
|
High level behavior (mixed):
|
|
============================
|
|
|
|
1), kernel(driver):
|
|
- calls request_firmware(&fw_entry, $FIRMWARE, device)
|
|
- kernel searchs the fimware image with name $FIRMWARE directly
|
|
in the below search path of root filesystem:
|
|
User customized search path by module parameter 'path'[1]
|
|
"/lib/firmware/updates/" UTS_RELEASE,
|
|
"/lib/firmware/updates",
|
|
"/lib/firmware/" UTS_RELEASE,
|
|
"/lib/firmware"
|
|
- If found, goto 7), else goto 2)
|
|
|
|
[1], the 'path' is a string parameter which length should be less
|
|
than 256, user should pass 'firmware_class.path=$CUSTOMIZED_PATH'
|
|
if firmware_class is built in kernel(the general situation)
|
|
|
|
2), userspace:
|
|
- /sys/class/firmware/xxx/{loading,data} appear.
|
|
- hotplug gets called with a firmware identifier in $FIRMWARE
|
|
and the usual hotplug environment.
|
|
- hotplug: echo 1 > /sys/class/firmware/xxx/loading
|
|
|
|
3), kernel: Discard any previous partial load.
|
|
|
|
4), userspace:
|
|
- hotplug: cat appropriate_firmware_image > \
|
|
/sys/class/firmware/xxx/data
|
|
|
|
5), kernel: grows a buffer in PAGE_SIZE increments to hold the image as it
|
|
comes in.
|
|
|
|
6), userspace:
|
|
- hotplug: echo 0 > /sys/class/firmware/xxx/loading
|
|
|
|
7), kernel: request_firmware() returns and the driver has the firmware
|
|
image in fw_entry->{data,size}. If something went wrong
|
|
request_firmware() returns non-zero and fw_entry is set to
|
|
NULL.
|
|
|
|
8), kernel(driver): Driver code calls release_firmware(fw_entry) releasing
|
|
the firmware image and any related resource.
|
|
|
|
High level behavior (driver code):
|
|
==================================
|
|
|
|
if(request_firmware(&fw_entry, $FIRMWARE, device) == 0)
|
|
copy_fw_to_device(fw_entry->data, fw_entry->size);
|
|
release_firmware(fw_entry);
|
|
|
|
Sample/simple hotplug script:
|
|
============================
|
|
|
|
# Both $DEVPATH and $FIRMWARE are already provided in the environment.
|
|
|
|
HOTPLUG_FW_DIR=/usr/lib/hotplug/firmware/
|
|
|
|
echo 1 > /sys/$DEVPATH/loading
|
|
cat $HOTPLUG_FW_DIR/$FIRMWARE > /sys/$DEVPATH/data
|
|
echo 0 > /sys/$DEVPATH/loading
|
|
|
|
Random notes:
|
|
============
|
|
|
|
- "echo -1 > /sys/class/firmware/xxx/loading" will cancel the load at
|
|
once and make request_firmware() return with error.
|
|
|
|
- firmware_data_read() and firmware_loading_show() are just provided
|
|
for testing and completeness, they are not called in normal use.
|
|
|
|
- There is also /sys/class/firmware/timeout which holds a timeout in
|
|
seconds for the whole load operation.
|
|
|
|
- request_firmware_nowait() is also provided for convenience in
|
|
user contexts to request firmware asynchronously, but can't be called
|
|
in atomic contexts.
|
|
|
|
|
|
about in-kernel persistence:
|
|
---------------------------
|
|
Under some circumstances, as explained below, it would be interesting to keep
|
|
firmware images in non-swappable kernel memory or even in the kernel image
|
|
(probably within initramfs).
|
|
|
|
Note that this functionality has not been implemented.
|
|
|
|
- Why OPTIONAL in-kernel persistence may be a good idea sometimes:
|
|
|
|
- If the device that needs the firmware is needed to access the
|
|
filesystem. When upon some error the device has to be reset and the
|
|
firmware reloaded, it won't be possible to get it from userspace.
|
|
e.g.:
|
|
- A diskless client with a network card that needs firmware.
|
|
- The filesystem is stored in a disk behind an scsi device
|
|
that needs firmware.
|
|
- Replacing buggy DSDT/SSDT ACPI tables on boot.
|
|
Note: this would require the persistent objects to be included
|
|
within the kernel image, probably within initramfs.
|
|
|
|
And the same device can be needed to access the filesystem or not depending
|
|
on the setup, so I think that the choice on what firmware to make
|
|
persistent should be left to userspace.
|
|
|
|
about firmware cache:
|
|
--------------------
|
|
After firmware cache mechanism is introduced during system sleep,
|
|
request_firmware can be called safely inside device's suspend and
|
|
resume callback, and callers needn't cache the firmware by
|
|
themselves any more for dealing with firmware loss during system
|
|
resume.
|