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Diffstat (limited to 'Documentation/networking/caif/spi_porting.txt')
| -rw-r--r-- | Documentation/networking/caif/spi_porting.txt | 208 |
1 files changed, 0 insertions, 208 deletions
diff --git a/Documentation/networking/caif/spi_porting.txt b/Documentation/networking/caif/spi_porting.txt deleted file mode 100644 index 9efd0687dc4c..000000000000 --- a/Documentation/networking/caif/spi_porting.txt +++ /dev/null @@ -1,208 +0,0 @@ -- 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 - functions: - - 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 addresses, 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 / Daniel.Martensson@stericsson.com - * 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> - -MODULE_LICENSE("GPL"); - -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. */ - - return IRQ_HANDLED; -} - -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 receive 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; - slave.sdev.name = "spi_sspi"; - slave_device.dev.release = sspi_release; - - /* Initialize platform device. */ - slave_device.name = "cfspi_sspi"; - slave_device.dev.platform_data = &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) -{ - platform_device_del(&slave_device); -} - -module_init(sspi_init); -module_exit(sspi_exit); |