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196 lines
7.6 KiB
196 lines
7.6 KiB
Introduction
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============
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Glink packet drivers are companion adaptation driver which use the kernel APIs
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to expose the Glink core logical channels as charecter devices to the
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user-space clients.
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The Glink core APIs are detailed in Documentation/arm/msm/glink.txt.
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Software description
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====================
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Glink packet drivers supports the Glink core APIs to user-space client through
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standard file operations like open, read, write, ioctl, poll and release etc.
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The standard Linux permissions are used for the device node and SELinux does
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further security checks.
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Device node [0..n]
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-------------------
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| VFS Framework |
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-------------------
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------- -------
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| CDEV | | CDEV |
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| Dev 0 |...| Dev n |
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----------------------
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| Glink packet driver |
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----------------------
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-----------------
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| G-Link core |
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-----------------
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To Remote System
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The file operations map to the G-link client API as follows:
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Open():
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----------
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The Open system call is mapped to glink_open() which opens a channel. The
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expected channel configuration has to done through DT files. The full DT schema
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is detailed in Documentation/devicetree/bindings/arm/msm/glinkpkt.txt.
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Open on the glink packet character device is a blocking call which blocks until
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the channel is fully open by both local processor and remote processor.
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Clients can configure the blocking time through a device configurable parameter
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defined per device.
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The timeout value is specified in seconds with a default timeout of 1 second.
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A negative value indicates an infinite wait.
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Example:
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# get open timeout value
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cat /sys/class/glinkpkt/device_name/open_timeout
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# set to 20 seconds value
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echo 20 > /sys/class/glinkpkt/device_name/open_timeout
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If the channel is not opened by remote processor or any other problem which
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fails the channel to be ready will result in timeout and -ETIMEOUT will return
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to client. Open on success returns the valid file descriptor to client and on
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fail case standard Linux error codes.
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The same device can be opened by multiple clients but passing the same file
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descriptor from multiple threads may lead unexpected results.
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Write():
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----------
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The Write system call is mapped to glink_tx() which transmits the data over the
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glink channel.
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Read():
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----------
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The Read system call consumes any pending data on the channel. Glink signals
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incoming data through the glink_notify_rx() call back and the glink packet
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driver queues the data internally and provides to client through read system
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call. Once the Read is completed, the glink packet driver calls glink_rx_done()
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API to notify the completion of receiving operation to Glink core.
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+
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User-Space | Kernel-Space
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+---------+ | +----------+ +------------+
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| Local | | | GlinkPKT | | |
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| Client | | | Driver | | Glink core |
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| | | | | | |
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+---------+ | +----------+ +------------+
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+ | + +
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| open() | glink_pkt_open() | glink_open() |
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| +--------------> | +-----------------> | +-----------------> |
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| | | |
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| File Handle[fd]| Valid Fd | Handle |
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| <--------------+ | <-----------------+ | <-----------------+ |
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| Ioctl() | | |
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| QUEUE_RX_INTENT | glink_pkt_ioctl() | glink_queue_rx_intent()
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| +--------------> | +-----------------> | +-----------------> |
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| | | |
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| <----------------------------------------------------------+ |
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| Read() | glink_pkt_read() | |
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| +--------------> | +-----------------> | +---+ |
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| | | | |
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| | Wait for data |
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| | | <---+ |
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| | | glink_notify_rx() |
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| | | <-----------------+ |
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| | Wake-up read() | |
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| | copy_to_user() | |
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| read() return | <-----------------+ | |
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| <--------------+ | | |
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+ | + +
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Clients can also poll on device node for POLLIN mask to get notification for
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any incoming data. Clients have to call the GLINK_PKT_IOCTL_QUEUE_RX_INTENT
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ioctl to queue the RX buffer to glink core in advance.
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Release():
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----------
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The Release system call is mapped to glink_close() to close a channel and free
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the resources.
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Poll():
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----------
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The Poll system call provides waiting operation like wait for incoming data on
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POLLIN mask and to get the TIOCM signal notification on POLLPRI mask. Clients
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can wait on poll for POLLPRI mask to get any notification regarding TICOM
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signals. In SSR case Poll call will return with POLLHUP mask and in this case
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client has to close and re-open the port.
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* POLLPRI - TIOCM bits changed
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* POLLIN - RX data available
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* POLLHUP - link is down due to either remote side closing or an SSR
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Ioctl():
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----------
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Multiple ioctls are supported to get the TICOM signal status and to queue the
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Rx intent with Glink core. Supported ioctls are TIOCMSET, TIOCMGET, TIOCMBIS,
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TIOCMBIC and GLINK_PKT_IOCTL_QUEUE_RX_INTENT.
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The GLINK_PKT_IOCTL_QUEUE_RX_INTENT ioctl is mapped to glink_queue_rx_intent()
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API which queues an RX intent with Glink core.
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Signals:
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==========
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Glink protocol provoide 32-bit control signal field to pass through for the
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clients-specific signaling where as Glink packet driver client which are from
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user space can use the signal filed as mentioned below.
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* 31:28 - Reserved for SMD RS-232 signals
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* 27:16 - Pass through for client usage
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* 15:0 - TICOM bits
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SSR operation:
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==============
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On remote subsystem restart all open channels on that edge will be closed and
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local clients have to close and re-open the channel to re-start the
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communication. All blocking calls such as open, read and write will be returned
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with -ENETRESET and the poll call will be return with the POLLHUP error codes.
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Files:
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==========
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Documentation/devicetree/bindings/arm/msm/glinkpkt.txt
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drivers/soc/qcom/msm_glink_pkt.c
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Wakelock:
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==========
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By default, GLINK PKT will acquire a wakelock for 2 seconds. To optimize this
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behavior, use the poll() function:
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1. Client calls poll() which blocks until data is available to read
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2. Data comes in, GLINK PKT grabs a wakelock and poll()is unblocked
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3. Client grabs wakelock to prevent system from suspending
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4. Client calls GLINK PKT read() to read the data
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5. GLINK PKT releases its wakelock
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6. Client Processes the data
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7. Client releases the wakelock
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Logging:
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==========
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cat /d/ipc_logging/glink_pkt/log_cont
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