http://www.mamicode.com/info-detail-472955.html

整體思路借鑑上文

背景知識

總所周知,mt7620有兩個獨立的硬體spi介面,且對應的片選cs為cs0與cs1.如果讀者朋友對spi匯流排的通訊協議略懂的話,會發現:spi的通訊是按照message的方式來進行的,一次通訊過程是通過transfer_one_message的方法來實現.實際上是對spi硬體介面的分時複用.如果我們能夠找到辦法,擴充一下cs片選訊號,且保留對spi硬體的分時複用,不就可以完美實現我們的目標了?那麼問題來了:如何擴充cs片選?如何讓spi硬體不產生衝突?具體如何實現?各位看官莫急,且聽我慢慢道來.

實現過程

dts檔案的奧祕

dts檔案中有很多隱藏關卡(不要問我為神馬知道這麼多,因為我喜歡看驅動原始碼,嘿嘿^_^),通過簡單的改動,就可以讓spi憑空多出cs片選來.

[email protected] {
            compatible ="ralink,rt5350-spi";
            status ="okay";
            cs-gpios =<0>,<0>,<&gpio3 01>;...};

怎麼樣?就這麼簡(REN)單(XING),就能為spi匯流排新增一個用gpio口線實現的片選cs2(這個處理過程,實際上是在spi.c中完成的,讀者朋友花點時間看看這個檔案便能豁然開朗).在進行下面的講解之前,讓我再囉嗦幾句,cs-gpio前面的<0>,<0>表示使用系統預設的cs0,與cs1,而cs2則繫結到gpio72.接下來,我們就要對驅動進行相應的修改,使之能夠配合我們新指定的cs.

修改spi-rt2880.c

新增標頭檔案

由於要用到gpio口,所以需要在檔案開頭 
#include <linux/gpio.h>

修改巨集定義

讓mt7620的第二個spi成為分時複用的硬體介面,修改如下:

// manfeel, try to add more cs pins(>2)#define M(cs)(cs ?1: cs)#define RAMIPS_SPI_STAT(cs)(0x00+(M(cs)* RAMIPS_SPI_DEV_OFFSET))#define RAMIPS_SPI_CFG(cs)(0x10+(M(cs)* RAMIPS_SPI_DEV_OFFSET))#define
 
 RAMIPS_SPI_CTL(cs)(0x14+(M(cs)* RAMIPS_SPI_DEV_OFFSET))#define RAMIPS_SPI_DATA(cs)(0x20+(M(cs)* RAMIPS_SPI_DEV_OFFSET))#define RAMIPS_SPI_FIFO_STAT(cs)(0x38+(M(cs)* RAMIPS_SPI_DEV_OFFSET))

也就是說,當cs>=1的時候,第二個spi介面負責所有的通訊工作.

改動rt2880_spi_setup

staticint rt2880_spi_setup(struct spi_device *spi){struct rt2880_spi *rs = spidev_to_rt2880_spi(spi);int status =0;if((spi->max_speed_hz ==0)||(spi->max_speed_hz >(rs->sys_freq /2)))
        spi->max_speed_hz =(rs->sys_freq /2);if(spi->max_speed_hz <(rs->sys_freq /128)){
        dev_err(&spi->dev,"setup: requested speed is too low %d Hz\n",
            spi->max_speed_hz);return-EINVAL;}// manfeel, set cs_gpioint cs = spi->cs_gpio;if(cs >=0){
        status = gpio_request(cs, dev_name(&spi->dev));
        dev_info(spi->master->dev.parent,"in %s, cs_gpio = %d, status = %d\n",__func__, cs, status);if(status)return status;
        status = gpio_direction_output(cs,!(spi->mode & SPI_CS_HIGH));}/*
     * baudrate & width will be set rt2880_spi_setup_transfer
     */return status;}

注意spi->cs_gpio,與dts中的cs-gpios對應,其值分別為-2,-2,72.-2表示沒有對應的gpio(由系統硬體實現片選).

修改rt2880_spi_set_cs

staticvoid rt2880_spi_set_cs(struct spi_device *spi,int enable){struct rt2880_spi *rs = spidev_to_rt2880_spi(spi);int cs = spi->chip_select;// manfeel, deal cs_gpio firstif(spi->cs_gpio >=0){/* SPI is normally active-low */
        gpio_set_value_cansleep(spi->cs_gpio,(spi->mode & SPI_CS_HIGH)? enable :!enable);}else{if(enable)
            rt2880_spi_clrbits(rs, RAMIPS_SPI_CTL(cs), SPICTL_SPIENA);else
            rt2880_spi_setbits(rs, RAMIPS_SPI_CTL(cs), SPICTL_SPIENA);}}

以上是摘錄過來的，下面是我的修改

在dts檔案中共設定了3個spi-flash，使用快速模式

[email protected] {
compatible = "ralink,rt5350-spi";
status = "okay";
cs-gpios = <0>, <0>, <&gpio0 1 1>;

[email protected] {
#address-cells = <1>;
#size-cells = <1>;
compatible = "w25q128";
reg = <0 0>;
linux,modalias = "m25p80";
spi-max-frequency = <40000000>;
m25p,fast-read;


[email protected] {
label = "u-boot";
reg = <0x0 0x30000>;
read-only;
};


[email protected] {
label = "u-boot-env";
reg = <0x30000 0x10000>;
read-only;
};


factory: [email protected] {
label = "factory";
reg = <0x40000 0x10000>;
read-only;
};


[email protected] {
label = "firmware";
reg = <0x50000 0xfb0000>;
};
};
en25q128 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "w25q128";
reg = <1 0>;
linux,modalias = "m25p80";
spi-max-frequency = <40000000>;
m25p,fast-read;


[email protected] {
label = "extflash1";
reg = <0x0 0x100000>;
};
};
en25q128 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "w25q128";
reg = <2 0>;
linux,modalias = "m25p80";
spi-max-frequency = <40000000>;
m25p,fast-read;


[email protected] {
label = "extflash2";
reg = <0x0 0x100000>;
};
};
};