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Diffstat (limited to 'Documentation/firmware_class/README')
| -rw-r--r-- | Documentation/firmware_class/README | 60 |
1 files changed, 32 insertions, 28 deletions
diff --git a/Documentation/firmware_class/README b/Documentation/firmware_class/README index 43e836c07ae..43fada989e6 100644 --- a/Documentation/firmware_class/README +++ b/Documentation/firmware_class/README @@ -1,7 +1,7 @@ request_firmware() hotplug interface: ------------------------------------ - Copyright (C) 2003 Manuel Estrada Sainz <ranty@debian.org> + Copyright (C) 2003 Manuel Estrada Sainz Why: --- @@ -18,32 +18,45 @@ High level behavior (mixed): ============================ - kernel(driver): calls request_firmware(&fw_entry, $FIRMWARE, device) - - userspace: + 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 - kernel: Discard any previous partial load. + 3), kernel: Discard any previous partial load. - userspace: + 4), 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 + 5), kernel: grows a buffer in PAGE_SIZE increments to hold the image as it comes in. - userspace: + 6), userspace: - hotplug: echo 0 > /sys/class/firmware/xxx/loading - kernel: request_firmware() returns and the driver has the firmware + 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. - kernel(driver): Driver code calls release_firmware(fw_entry) releasing + 8), kernel(driver): Driver code calls release_firmware(fw_entry) releasing the firmware image and any related resource. High level behavior (driver code): @@ -77,7 +90,8 @@ seconds for the whole load operation. - request_firmware_nowait() is also provided for convenience in - non-user contexts. + user contexts to request firmware asynchronously, but can't be called + in atomic contexts. about in-kernel persistence: @@ -105,20 +119,10 @@ on the setup, so I think that the choice on what firmware to make persistent should be left to userspace. - - Why register_firmware()+__init can be useful: - - For boot devices needing firmware. - - To make the transition easier: - The firmware can be declared __init and register_firmware() - called on module_init. Then the firmware is warranted to be - there even if "firmware hotplug userspace" is not there yet or - it doesn't yet provide the needed firmware. - Once the firmware is widely available in userspace, it can be - removed from the kernel. Or made optional (CONFIG_.*_FIRMWARE). - - In either case, if firmware hotplug support is there, it can move the - firmware out of kernel memory into the real filesystem for later - usage. - - Note: If persistence is implemented on top of initramfs, - register_firmware() may not be appropriate. - + 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 need't cache the firmware by + themselves any more for dealing with firmware loss during system + resume. |