Commit 529d6dad authored by Sjur Braendeland's avatar Sjur Braendeland Committed by David S. Miller

caif-driver: Add CAIF-SPI Protocol driver.

This patch introduces the CAIF SPI Protocol Driver for
CAIF Link Layer.

This driver implements a platform driver to accommodate for a
platform specific SPI device. A general platform driver is not
possible as there are no SPI Slave side Kernel API defined.
A sample CAIF SPI Platform device can be found in
Signed-off-by: default avatarSjur Braendeland <>
Signed-off-by: default avatarDavid S. Miller <>
parent 01eebb53
- CAIF SPI porting -
- CAIF SPI basics:
Running CAIF over SPI needs some extra setup, owing to the nature of SPI.
Two extra GPIOs have been added in order to negotiate the transfers
between the master and the slave. The minimum requirement for running
CAIF over SPI is a SPI slave chip and two GPIOs (more details below).
Please note that running as a slave implies that you need to keep up
with the master clock. An overrun or underrun event is fatal.
- CAIF SPI framework:
To make porting as easy as possible, the CAIF SPI has been divided in
two parts. The first part (called the interface part) deals with all
generic functionality such as length framing, SPI frame negotiation
and SPI frame delivery and transmission. The other part is the CAIF
SPI slave device part, which is the module that you have to write if
you want to run SPI CAIF on a new hardware. This part takes care of
the physical hardware, both with regard to SPI and to GPIOs.
- Implementing a CAIF SPI device:
- Functionality provided by the CAIF SPI slave device:
In order to implement a SPI device you will, as a minimum,
need to implement the following
int (*init_xfer) (struct cfspi_xfer * xfer, struct cfspi_dev *dev):
This function is called by the CAIF SPI interface to give
you a chance to set up your hardware to be ready to receive
a stream of data from the master. The xfer structure contains
both physical and logical adresses, as well as the total length
of the transfer in both directions.The dev parameter can be used
to map to different CAIF SPI slave devices.
void (*sig_xfer) (bool xfer, struct cfspi_dev *dev):
This function is called by the CAIF SPI interface when the output
(SPI_INT) GPIO needs to change state. The boolean value of the xfer
variable indicates whether the GPIO should be asserted (HIGH) or
deasserted (LOW). The dev parameter can be used to map to different CAIF
SPI slave devices.
- Functionality provided by the CAIF SPI interface:
void (*ss_cb) (bool assert, struct cfspi_ifc *ifc);
This function is called by the CAIF SPI slave device in order to
signal a change of state of the input GPIO (SS) to the interface.
Only active edges are mandatory to be reported.
This function can be called from IRQ context (recommended in order
not to introduce latency). The ifc parameter should be the pointer
returned from the platform probe function in the SPI device structure.
void (*xfer_done_cb) (struct cfspi_ifc *ifc);
This function is called by the CAIF SPI slave device in order to
report that a transfer is completed. This function should only be
called once both the transmission and the reception are completed.
This function can be called from IRQ context (recommended in order
not to introduce latency). The ifc parameter should be the pointer
returned from the platform probe function in the SPI device structure.
- Connecting the bits and pieces:
- Filling in the SPI slave device structure:
Connect the necessary callback functions.
Indicate clock speed (used to calculate toggle delays).
Chose a suitable name (helps debugging if you use several CAIF
SPI slave devices).
Assign your private data (can be used to map to your structure).
- Filling in the SPI slave platform device structure:
Add name of driver to connect to ("cfspi_sspi").
Assign the SPI slave device structure as platform data.
- Padding:
In order to optimize throughput, a number of SPI padding options are provided.
Padding can be enabled independently for uplink and downlink transfers.
Padding can be enabled for the head, the tail and for the total frame size.
The padding needs to be correctly configured on both sides of the link.
The padding can be changed via module parameters in cfspi_sspi.c or via
the sysfs directory of the cfspi_sspi driver (before device registration).
- CAIF SPI device template:
* Copyright (C) ST-Ericsson AB 2010
* Author: Daniel Martensson /
* License terms: GNU General Public License (GPL), version 2.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/interrupt.h>
#include <linux/dma-mapping.h>
#include <net/caif/caif_spi.h>
struct sspi_struct {
struct cfspi_dev sdev;
struct cfspi_xfer *xfer;
static struct sspi_struct slave;
static struct platform_device slave_device;
static irqreturn_t sspi_irq(int irq, void *arg)
/* You only need to trigger on an edge to the active state of the
* SS signal. Once a edge is detected, the ss_cb() function should be
* called with the parameter assert set to true. It is OK
* (and even advised) to call the ss_cb() function in IRQ context in
* order not to add any delay. */
static void sspi_complete(void *context)
/* Normally the DMA or the SPI framework will call you back
* in something similar to this. The only thing you need to
* do is to call the xfer_done_cb() function, providing the pointer
* to the CAIF SPI interface. It is OK to call this function
* from IRQ context. */
static int sspi_init_xfer(struct cfspi_xfer *xfer, struct cfspi_dev *dev)
/* Store transfer info. For a normal implementation you should
* set up your DMA here and make sure that you are ready to
* receive the data from the master SPI. */
struct sspi_struct *sspi = (struct sspi_struct *)dev->priv;
sspi->xfer = xfer;
return 0;
void sspi_sig_xfer(bool xfer, struct cfspi_dev *dev)
/* If xfer is true then you should assert the SPI_INT to indicate to
* the master that you are ready to recieve the data from the master
* SPI. If xfer is false then you should de-assert SPI_INT to indicate
* that the transfer is done.
struct sspi_struct *sspi = (struct sspi_struct *)dev->priv;
static void sspi_release(struct device *dev)
* Here you should release your SPI device resources.
static int __init sspi_init(void)
/* Here you should initialize your SPI device by providing the
* necessary functions, clock speed, name and private data. Once
* done, you can register your device with the
* platform_device_register() function. This function will return
* with the CAIF SPI interface initialized. This is probably also
* the place where you should set up your GPIOs, interrupts and SPI
* resources. */
int res = 0;
/* Initialize slave device. */
slave.sdev.init_xfer = sspi_init_xfer;
slave.sdev.sig_xfer = sspi_sig_xfer;
slave.sdev.clk_mhz = 13;
slave.sdev.priv = &slave; = "spi_sspi"; = sspi_release;
/* Initialize platform device. */ = "cfspi_sspi"; = &slave.sdev;
/* Register platform device. */
res = platform_device_register(&slave_device);
if (res) {
printk(KERN_WARNING "sspi_init: failed to register dev.\n");
return -ENODEV;
return res;
static void __exit sspi_exit(void)
......@@ -12,3 +12,22 @@ config CAIF_TTY
The CAIF TTY transport driver is a Line Discipline (ldisc)
identified as N_CAIF. When this ldisc is opened from user space
it will redirect the TTY's traffic into the CAIF stack.
tristate "CAIF SPI transport driver for slave interface"
depends on CAIF
default n
The CAIF Link layer SPI Protocol driver for Slave SPI interface.
This driver implements a platform driver to accommodate for a
platform specific SPI device. A sample CAIF SPI Platform device is
provided in Documentation/networking/caif/spi_porting.txt
bool "Next command and length in start of frame"
depends on CAIF_SPI_SLAVE
default n
Putting the next command and length in the start of the frame can
help to synchronize to the next transfer in case of over or under-runs.
This option also needs to be enabled on the modem.
......@@ -4,3 +4,7 @@ endif
# Serial interface
obj-$(CONFIG_CAIF_TTY) += caif_serial.o
# SPI slave physical interfaces module
cfspi_slave-objs := caif_spi.o caif_spi_slave.o
obj-$(CONFIG_CAIF_SPI_SLAVE) += cfspi_slave.o
This diff is collapsed.
* Copyright (C) ST-Ericsson AB 2010
* Contact: Sjur Brendeland /
* Author: Daniel Martensson /
* License terms: GNU General Public License (GPL) version 2.
#include <linux/version.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/string.h>
#include <linux/semaphore.h>
#include <linux/workqueue.h>
#include <linux/completion.h>
#include <linux/list.h>
#include <linux/interrupt.h>
#include <linux/dma-mapping.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/debugfs.h>
#include <net/caif/caif_spi.h>
static inline int forward_to_spi_cmd(struct cfspi *cfspi)
return cfspi->rx_cpck_len;
#define SPI_DATA_POS 0
static inline int forward_to_spi_cmd(struct cfspi *cfspi)
return 0;
int spi_frm_align = 2;
int spi_up_head_align = 1;
int spi_up_tail_align;
int spi_down_head_align = 3;
int spi_down_tail_align = 1;
static inline void debugfs_store_prev(struct cfspi *cfspi)
/* Store previous command for debugging reasons.*/
cfspi->pcmd = cfspi->cmd;
/* Store previous transfer. */
cfspi->tx_ppck_len = cfspi->tx_cpck_len;
cfspi->rx_ppck_len = cfspi->rx_cpck_len;
static inline void debugfs_store_prev(struct cfspi *cfspi)
void cfspi_xfer(struct work_struct *work)
struct cfspi *cfspi;
u8 *ptr = NULL;
unsigned long flags;
int ret;
cfspi = container_of(work, struct cfspi, work);
/* Initialize state. */
cfspi->cmd = SPI_CMD_EOT;
for (;;) {
cfspi_dbg_state(cfspi, CFSPI_STATE_WAITING);
/* Wait for master talk or transmit event. */
test_bit(SPI_XFER, &cfspi->state) ||
test_bit(SPI_TERMINATE, &cfspi->state));
if (test_bit(SPI_TERMINATE, &cfspi->state))
/* Prefill buffers for easier debugging. */
memset(cfspi->xfer.va_tx, 0xFF, SPI_DMA_BUF_LEN);
memset(cfspi->xfer.va_rx, 0xFF, SPI_DMA_BUF_LEN);
#endif /* CFSPI_DBG_PREFILL */
cfspi_dbg_state(cfspi, CFSPI_STATE_AWAKE);
/* Check whether we have a committed frame. */
if (cfspi->tx_cpck_len) {
int len;
cfspi_dbg_state(cfspi, CFSPI_STATE_FETCH_PKT);
/* Copy commited SPI frames after the SPI indication. */
ptr = (u8 *) cfspi->xfer.va_tx;
ptr += SPI_IND_SZ;
len = cfspi_xmitfrm(cfspi, ptr, cfspi->tx_cpck_len);
WARN_ON(len != cfspi->tx_cpck_len);
cfspi_dbg_state(cfspi, CFSPI_STATE_GET_NEXT);
/* Get length of next frame to commit. */
cfspi->tx_npck_len = cfspi_xmitlen(cfspi);
WARN_ON(cfspi->tx_npck_len > SPI_DMA_BUF_LEN);
* Add indication and length at the beginning of the frame,
* using little endian.
ptr = (u8 *) cfspi->xfer.va_tx;
*ptr++ = SPI_CMD_IND;
*ptr++ = (SPI_CMD_IND & 0xFF00) >> 8;
*ptr++ = cfspi->tx_npck_len & 0x00FF;
*ptr++ = (cfspi->tx_npck_len & 0xFF00) >> 8;
/* Calculate length of DMAs. */
cfspi->xfer.tx_dma_len = cfspi->tx_cpck_len + SPI_IND_SZ;
cfspi->xfer.rx_dma_len = cfspi->rx_cpck_len + SPI_CMD_SZ;
/* Add SPI TX frame alignment padding, if necessary. */
if (cfspi->tx_cpck_len &&
(cfspi->xfer.tx_dma_len % spi_frm_align)) {
cfspi->xfer.tx_dma_len += spi_frm_align -
(cfspi->xfer.tx_dma_len % spi_frm_align);
/* Add SPI RX frame alignment padding, if necessary. */
if (cfspi->rx_cpck_len &&
(cfspi->xfer.rx_dma_len % spi_frm_align)) {
cfspi->xfer.rx_dma_len += spi_frm_align -
(cfspi->xfer.rx_dma_len % spi_frm_align);
cfspi_dbg_state(cfspi, CFSPI_STATE_INIT_XFER);
/* Start transfer. */
ret = cfspi->dev->init_xfer(&cfspi->xfer, cfspi->dev);
cfspi_dbg_state(cfspi, CFSPI_STATE_WAIT_ACTIVE);
* TODO: We might be able to make an assumption if this is the
* first loop. Make sure that minimum toggle time is respected.
cfspi_dbg_state(cfspi, CFSPI_STATE_SIG_ACTIVE);
/* Signal that we are ready to recieve data. */
cfspi->dev->sig_xfer(true, cfspi->dev);
cfspi_dbg_state(cfspi, CFSPI_STATE_WAIT_XFER_DONE);
/* Wait for transfer completion. */
cfspi_dbg_state(cfspi, CFSPI_STATE_XFER_DONE);
if (cfspi->cmd == SPI_CMD_EOT) {
* Clear the master talk bit. A xfer is always at
* least two bursts.
clear_bit(SPI_SS_ON, &cfspi->state);
cfspi_dbg_state(cfspi, CFSPI_STATE_WAIT_INACTIVE);
/* Make sure that the minimum toggle time is respected. */
if (SPI_XFER_TIME_USEC(cfspi->xfer.tx_dma_len,
cfspi->dev->clk_mhz) <
(cfspi->xfer.tx_dma_len, cfspi->dev->clk_mhz));
cfspi_dbg_state(cfspi, CFSPI_STATE_SIG_INACTIVE);
/* De-assert transfer signal. */
cfspi->dev->sig_xfer(false, cfspi->dev);
/* Check whether we received a CAIF packet. */
if (cfspi->rx_cpck_len) {
int len;
cfspi_dbg_state(cfspi, CFSPI_STATE_DELIVER_PKT);
/* Parse SPI frame. */
ptr = ((u8 *)(cfspi->xfer.va_rx + SPI_DATA_POS));
len = cfspi_rxfrm(cfspi, ptr, cfspi->rx_cpck_len);
WARN_ON(len != cfspi->rx_cpck_len);
/* Check the next SPI command and length. */
ptr = (u8 *) cfspi->xfer.va_rx;
ptr += forward_to_spi_cmd(cfspi);
cfspi->cmd = *ptr++;
cfspi->cmd |= ((*ptr++) << 8) & 0xFF00;
cfspi->rx_npck_len = *ptr++;
cfspi->rx_npck_len |= ((*ptr++) << 8) & 0xFF00;
WARN_ON(cfspi->rx_npck_len > SPI_DMA_BUF_LEN);
WARN_ON(cfspi->cmd > SPI_CMD_EOT);
/* Check whether the master issued an EOT command. */
if (cfspi->cmd == SPI_CMD_EOT) {
/* Reset state. */
cfspi->tx_cpck_len = 0;
cfspi->rx_cpck_len = 0;
} else {
/* Update state. */
cfspi->tx_cpck_len = cfspi->tx_npck_len;
cfspi->rx_cpck_len = cfspi->rx_npck_len;
* Check whether we need to clear the xfer bit.
* Spin lock needed for packet insertion.
* Test and clear of different bits
* are not supported.
spin_lock_irqsave(&cfspi->lock, flags);
if (cfspi->cmd == SPI_CMD_EOT && !cfspi_xmitlen(cfspi)
&& !test_bit(SPI_SS_ON, &cfspi->state))
clear_bit(SPI_XFER, &cfspi->state);
spin_unlock_irqrestore(&cfspi->lock, flags);
struct platform_driver cfspi_spi_driver = {
.probe = cfspi_spi_probe,
.remove = cfspi_spi_remove,
.driver = {
.name = "cfspi_sspi",
.owner = THIS_MODULE,
* Copyright (C) ST-Ericsson AB 2010
* Author: Daniel Martensson /
* License terms: GNU General Public License (GPL) version 2
#ifndef CAIF_SPI_H_
#define CAIF_SPI_H_
#include <net/caif/caif_device.h>
#define SPI_CMD_WR 0x00
#define SPI_CMD_RD 0x01
#define SPI_CMD_EOT 0x02
#define SPI_CMD_IND 0x04
#define SPI_DMA_BUF_LEN 8192
#define WL_SZ 2 /* 16 bits. */
#define SPI_CMD_SZ 4 /* 32 bits. */
#define SPI_IND_SZ 4 /* 32 bits. */
#define SPI_XFER 0
#define SPI_SS_ON 1
#define SPI_SS_OFF 2
/* Minimum time between different levels is 50 microseconds. */
/* Defines for calculating duration of SPI transfers for a particular
* number of bytes.
#define SPI_XFER_TIME_USEC(bytes, clk) (((bytes) * 8) / clk)
/* Normally this should be aligned on the modem in order to benefit from full
* duplex transfers. However a size of 8188 provokes errors when running with
* the modem. These errors occur when packet sizes approaches 4 kB of data.
#define CAIF_MAX_SPI_FRAME 4092
/* Maximum number of uplink CAIF frames that can reside in the same SPI frame.
* This number should correspond with the modem setting. The application side
* CAIF accepts any number of embedded downlink CAIF frames.
/* Decides if SPI buffers should be prefilled with 0xFF pattern for easier
* debugging. Both TX and RX buffers will be filled before the transfer.
/* Structure describing a SPI transfer. */
struct cfspi_xfer {
u16 tx_dma_len;
u16 rx_dma_len;
void *va_tx;
dma_addr_t pa_tx;
void *va_rx;
dma_addr_t pa_rx;
/* Structure implemented by the SPI interface. */
struct cfspi_ifc {
void (*ss_cb) (bool assert, struct cfspi_ifc *ifc);
void (*xfer_done_cb) (struct cfspi_ifc *ifc);
void *priv;
/* Structure implemented by SPI clients. */
struct cfspi_dev {
int (*init_xfer) (struct cfspi_xfer *xfer, struct cfspi_dev *dev);
void (*sig_xfer) (bool xfer, struct cfspi_dev *dev);
struct cfspi_ifc *ifc;
char *name;
u32 clk_mhz;
void *priv;
/* Enumeration describing the CAIF SPI state. */
enum cfspi_state {
/* Structure implemented by SPI physical interfaces. */
struct cfspi {
struct caif_dev_common cfdev;
struct net_device *ndev;
struct platform_device *pdev;
struct sk_buff_head qhead;
struct sk_buff_head chead;
u16 cmd;
u16 tx_cpck_len;
u16 tx_npck_len;
u16 rx_cpck_len;
u16 rx_npck_len;
struct cfspi_ifc ifc;
struct cfspi_xfer xfer;
struct cfspi_dev *dev;
unsigned long state;
struct work_struct work;
struct workqueue_struct *wq;
struct list_head list;
int flow_off_sent;
u32 qd_low_mark;
u32 qd_high_mark;
struct completion comp;
wait_queue_head_t wait;
spinlock_t lock;
bool flow_stop;
enum cfspi_state dbg_state;
u16 pcmd;
u16 tx_ppck_len;
u16 rx_ppck_len;
struct dentry *dbgfs_dir;
struct dentry *dbgfs_state;
struct dentry *dbgfs_frame;
#endif /* CONFIG_DEBUG_FS */