108 lines
3.6 KiB
Plaintext
108 lines
3.6 KiB
Plaintext
|
|
||
|
|
request_firmware() hotplug interface:
|
||
|
|
------------------------------------
|
||
|
|
Copyright (C) 2003 Manuel Estrada Sainz <ranty@debian.org>
|
||
|
|
|
||
|
|
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):
|
||
|
|
============================
|
||
|
|
|
||
|
|
kernel(driver): calls request_firmware(&fw_entry, $FIRMWARE, device)
|
||
|
|
|
||
|
|
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
|
||
|
|
|
||
|
|
kernel: Discard any previous partial load.
|
||
|
|
|
||
|
|
userspace:
|
||
|
|
- hotplug: cat appropriate_firmware_image > \
|
||
|
|
/sys/class/firmware/xxx/data
|
||
|
|
|
||
|
|
kernel: grows a buffer in PAGE_SIZE increments to hold the image as it
|
||
|
|
comes in.
|
||
|
|
|
||
|
|
userspace:
|
||
|
|
- hotplug: echo 0 > /sys/class/firmware/xxx/loading
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
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(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 > /sysfs/$DEVPATH/data
|
||
|
|
echo 0 > /sys/$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
|
||
|
|
non-user 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.
|
||
|
|
|