Cellular Modem Information » Qualcomm Linux Modems by Quectel & Co

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h1. Qualcomm Kernel

Random notes about the Qualcomm Kernel as used on the MDM9615 and MDM9x07.  May also apply to other Qualcomm Linux based systems such as Android smartphones.

h2. remote_spinlock

You probably know the regular spinlocks inside the linux kernel: They protect you from multiple processors entering the same critical section of code in the kernel.  All but one processor core will be busy-waiting while the spinlock is held.

In the Qualcomm multi-CPU SoCs they have implemented a remote spinlock mechanism, in which e.g. the APPS processor can prevent the MODEM processor from entering a critical section (or rather, access critical shared data between the processors).

h2. diag

Please see [[DIAG]] for more details on Qualcomm DIAG in the context of the modems we are documenting here.

h3. diag forwarding

<pre>

drivers/char/diag/diagfwd.[ch]

drivers/usb/gadget/f_diag.[ch]

drivers/usb/misc/diag_bridge.c

</pre>

* the usb diag gadget handles diag packet read/write over usb

* issues events like USB_DIAG_READ_DONE

* picked up by diagfwd.c

** can forward diag requests via SMD shared memory to other processors

h3. diag char

The kernel exports a /dev/diag char device which userspce processes can

use to register/listen for DIAG events from the system, or actually

register a DIAG 'subsystem' themselves which can then be controlled from

QXDM.

<pre>

drivers/char/diag/diagchar_core.c

</pre>

* ioctl()s for diag configuration

* supports several concurrent diag clients

* diag logging can be directed to USB/HSIC, character device and more

** {USB,CALLBACK,MEMORY_DEVICE,UART,NO_LOGGING}_MODE

drivers/char/diag/diag_dci.c

* DCI table is a routing table where pid/sockets can register for a

  given DCI.  socket close/cleanup code releases all DCI routes for

  that socket.

h4. DIAG_IOCTL_COMMAND_REG

* Register a new DIAG command so it can be used from the outside world (QXDM)

* use 'struct diag_cmd_reg_entry_t' per command

* driver keeps a driver->cmd_reg_list of registered commands

h4. DIAG_IOCTL_COMMAND_DEREG

* unregister debug command

h4. DIAG_IOCTL_GET_DELAYED_RSP_ID

h4. DIAG_IOCTL_DCI_REG

h4. DIAG_IOCTL_DCI_DEINIT

h4. DIAG_IOCTL_DCI_SUPPORT

h4. DIAG_IOCTL_DCI_HEALTH_STATS

h4. DIAG_IOCTL_DCI_LOG_STATUS

h4. DIAG_IOCTL_DCI_EVENT_STATUS

h4. DIAG_IOCTL_DCI_CLEAR_LOGS

h4. DIAG_IOCTL_DCI_CLEAR_EVENTS

h4. DIAG_IOCTL_LSM_DEINIT

h4. DIAG_IOCTL_SWITCH_LOGGING

* switch between USB and shared-memory diag

* 

h4. DIAG_IOCTL_REMOTE_DEV

h4. DIAG_IOCTL_VOTE_REAL_TIME

h4. DIAG_IOCTL_GET_REAL_TIME

h4. DIAG_IOCTL_PERIPHERAL_BUF_CONFIG

h4. DIAG_IOCTL_PERIPHERAL_BUF_DRAIN

h4. DIAG_IOCTL_REGISTER_CALLBACK

* doen't really do anything but checking arguments ?!?

h4. DIAG_IOCTL_HDLC_TOGGLE

enable or disable HDLC framing of /dev/diag

h2. IRSC (IPC Router Security Control)

FIXME

h2. SMD (shared memory)

See [[Qualcomm_Linux_SMD]]

h2. smem_log

This is some kidn of high speed shared memory based event log to which all processors can log events.

Userspace applications can use write() to @/dev/smem_log@ to add log entries.

Qualcomm uses a proprietary minimal shim layer offering SMEM_LOG_EVENT and SMEM_LOG_EVENT6 macros

that can be used to write events with an event ID plus three data words or six data words, respectively.

The shared memory log can be read from linux userspace via debugfs, see the devices in @/sys/kernel/debug/smem_log@

and simply use @cat@ on them. You will get lines like

<pre>

MODM: 3982377401 000d0000: 00000001: 03000019 01000028 01000015 53505041 00000061 5f696d71

MODM: 3982378159      QCSI: 00000004: 00040029 00240015 00000003 00000001 0000002b 00000000

MODM: 3982378619 000d0000: 00000001: 03000019 0100002b 01000015 53505041 00000061 5f696d71

APPS: 3982397356      QCCI: 00000005: 0004001d 0024000e 00000003 00000003 00000019 00000000

APPS: 3982400571      QCCI: 00000005: 00040029 0024000e 00000003 00000003 00000019 00000000

MODM: 1841235211      QCSI: 00000004: 0004001e 0024001c 00000003 00000001 00000028 00000000

MODM: 1841236665 000d0000: 00000001: 03000019 01000028 0101001c 53505041 00000061 5f696d71

MODM: 1841241411      QCSI: 00000004: 0004002a 0024001c 00000003 00000001 0000002b 00000000

MODM: 1841242246 000d0000: 00000001: 03000019 0100002b 0100001c 53505041 00000061 5f696d71

MODM: 1841243796      QCSI: 00000004: 0004002b 00660019 00000003 00000001 0000002b 00000000

MODM: 1841244286 000d0000: 00000001: 03000019 0100002b 01000019 53505041 00000061 5f696d71

APPS: 1841255456      QCCI: 00000005: 0004001e 00240015 00000003 00000003 00000019 00000000

MODM: 1841255335 000d0000: 00000002: 0100ffff 0300ffff 07000014 53505041 0000016c 74646d73

MODM: 1841255828 000d0000: 00000702: 00000001 00000028 00000007

APPS: 1841261430      QCCI: 00000005: 0004002a 00240015 00000003 00000003 00000019 00000000

</pre>

More information in @smem_log.h@

h2. rmnet

"remote network" ?

* consists of control channel and data channel

* data channel carries IP data

* control channel carries QMI messages

* drivers/net/ethernet/msm/msm_rmnet_bam.c

** ioctl() to set ethernet or rawip (RMNET_IOCTL_SET_LLP_ETHERNET, RMNET_IOCTL_SET_LLP_IP, RMNET_IOCTL_GET_LLP), initial boot time config is ETHERNET

** use msm_bam_dmux_open() to attach

** use RMNET_IOCTL_GET_EPID to get the BAM_DMUX endpoint id

h2. bam (Bus Access Manager/Module)

* The Bus Access Manager/Module (BAM) can be

  considered as a distributed data mover (DM)

* some kind of DMA controller/engine

* A number of the on-chip devices have their own BAM DMA controller

  and use it to move data between system memory and peripherals or

  between two peripherals.

Files:

<pre>

./drivers/dma/qcom_bam_dma.c

./drivers/net/ethernet/msm/msm_rmnet_bam.c

./drivers/platform/msm/sps/bam.c

./drivers/platform/msm/sps/sps_bam.c

./drivers/platform/msm/usb_bam.c

</pre>

* channels (BAM_DMUX_)

** RMNET_0...7

** USB_RMNET_0

** DATA_REV_RMNET_0..8

** USB_DPL

seem to be be based on dmux ./drivers/soc/qcom/bam_dmux.c

h2. IPA (Internet Packet Accelerator)

Internet Packet Accelerator (IPA) is a programmable protocol

processor HW block. It is designed to support generic HW processing

of UL/DL IP packets for various use cases independent of radio

technology.

See drivers/platform/msm/ipa/

http://www.sumobrain.com/patents/wipo/Accelerator/WO2013063791A1.pdf

h2. bam2bam

maybe soem kind of direct connection between two peripherals by means of the BAM?

h2. Android USB Gadget

see [[Android_USB_Gadget]]

h2. IPC Logging

see [[IPC_Logging]]