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iwlmei allows to integrate with the CSME firmware. There are
flows that are prioprietary for this purpose:
* Get the information of the AP the CSME firmware is connected
to. This is useful when we need to speed up the connection
process in case the CSME firmware has a TCP connection
that must be kept alive across the ownership transition.
* Forbid roaming, which will happen when the CSME firmware
wants to tell the user space not disrupt the connection.
* Request ownership, upon driver boot when the CSME firmware
owns the device. This is a notification sent by the kernel.
All those commands are expected to be used by any software
managing the connection (mainly NetworkManager). Those commands
are expected to be used only in case the CSME firmware owns
the device and doesn't want to release the device unless the
host made sure that it can keep the connectivity.
Here are the steps of the expected flow:
1) The machine boots while AMT has an active TCP connection
2) iwlwifi starts and tries to access the device
3) The device is not available because of the active TCP
connection. (If there are no active connections, the CSME
firmware would have allowed iwlwifi to use the device)
Note that all the steps up to here don't involve iwlmei. All
this happens in iwlwifi (in iwl_pcie_prepare_card_hw).
4) iwlmei establishes a connection to the CSME firmware (through
SAP)
Here iwlwifi uses iwlmei to access the device's capabilities
(since it can't touch the device), but this is not relevant
for the vendor commands.
5) The CSME firmware tells iwlmei that it uses the NIC and
that there is an acitve TCP connection, and hence, the
host needs to think twice before asking the CSME firmware
to release the device
6) iwlmei tells iwlwifi to report HW RFKILL with a special
reason
Up to here, there was no user space involved.
7) The user space (NetworkManager) boots and sees that the
device is in RFKILL because the host doesn't own the
device
8) The user space asks the kernel what AP the CSME firmware
is connected to (with the first vendor command mentionned
above)
9) The user space checks if it has a profile that matches the
reply from the CSME firmware
10) The user space installs a network to the wpa_supplicant
with a specific BSSID and a specific frequency
11) The user space prevents any type of full scan
12) The user space asks iwlmei to request ownership on the
device (with the third vendor command)
13) iwlmei request ownership from the CSME firmware
14) The CSME firmware grants ownership
15) iwlmei tells iwlwifi to lift the RFKILL
16) RFKILL OFF is reported to userspace
17) The host boots the device, loads the firwmare, and
connect to a specific BSSID without scanning including IP
in less than 600ms (this is what I measured, of course
it depends on many factors)
18) The host reports to the CSME firmware that there is a
connection
19) The TCP connection is preserved and the host has now
connectivity
20) Later, the TCP connection to the CSME firmware is
terminated
21) The CSME firmware tells iwlmei that it is now free to
do whatever it likes
22) iwlwifi sends the second vendor command to tell the
user space that it can remove the special network
configuration and pick any SSID / BSSID it likes.
Co-Developed-by: Ayala Beker <ayala.beker@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://lore.kernel.org/r/20210625081717.7680-4-emmanuel.grumbach@intel.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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