之前介紹了高通平臺對應GPIO狀態的查看https://mp.csdn.net/postedit/82345424。現在我們來看下MTK平臺是如何實現的。
一、節點位置
在MTK平臺,我們可以通過cat節點(mt_gpio)來查看對應的狀態。不同的平臺,該管腳對應的位置也是不同的,建議直接進入手機目錄查看:
adb shell
find -name "mt_gpio"
我這查看到對應的是:sys/devices/platform/1000b000.pinctrl/mt_gpio
然後直接cat這個節點會出現如下的信息:
PIN: [MODE] [DIR] [DOUT] [DIN] [PULL_EN] [PULL_SEL] [IES] [SMT] [DRIVE] ( [R1] [R0] )
0: 011110100 01
1: 000010100 01
2: 000111100 01
3: 000010100 01
4: 011100100 00
5: 000010100 01
6: 000100110
... ...
二、源碼分析
1、首先我們從創建該節點的位置開始分析,在kernel-4.4/drivers/pinctrl/mediatek/pinctrl-mtk-common.c
static DEVICE_ATTR(mt_gpio, 0664, mt_gpio_show_pin, mt_gpio_store_pin);
這裏可以看到通過DEVICE_ATTR創建了mt_gpio節點,開了664的權限。
2、再來看下當cat節點時的動作 mt_gpio_show_pin
static ssize_t mt_gpio_show_pin(struct device *dev, struct device_attribute *attr, char *buf)
{
int len = 0;
int bufLen = PAGE_SIZE;
struct mtk_pinctrl *pctl = dev_get_drvdata(dev);
struct gpio_chip *chip = pctl->chip;
unsigned i;
int mode, pull_val;
len += snprintf(buf+len, bufLen-len,
"PIN: [MODE] [DIR] [DOUT] [DIN] [PULL_EN] [PULL_SEL] [IES] [SMT] [DRIVE] ( [R1] [R0] )\n");
for (i = 0; i < chip->ngpio; i++) {
pull_val = mtk_pullsel_get(chip, i);
mode = mtk_pinmux_get(chip, i);
if (mode >= 0) {
len += snprintf(buf+len, bufLen-len, "%4d: %x%d%d%d%d%d%d%d%x",
i,
mtk_pinmux_get(chip, i),
!mtk_gpio_get_direction(chip, i),
mtk_gpio_get_out(chip, i),
mtk_gpio_get_in(chip, i),
mtk_pullen_get(chip, i),
(pull_val >= 0) ? (pull_val&1) : -1,
mtk_ies_get(chip, i),
mtk_smt_get(chip, i),
mtk_driving_get(chip, i));
if ((pull_val & 8) && (pull_val >= 0))
len += snprintf(buf+len, bufLen-len, " %d%d", !!(pull_val&4), !!(pull_val&2));
len += snprintf(buf+len, bufLen-len, "\n");
} else {
len += snprintf(buf+len, bufLen-len, "%4d: XXXXXXXXX\n", i);
}
}
return len;
}
3、分解對應的項
通過如上方法可以看到我們cat出來的信息分別對應的是:
PIN: [MODE] [DIR] [DOUT] [DIN] [PULL_EN] [PULL_SEL] [IES] [SMT] [DRIVE] ( [R1] [R0] )
PIN:即對應的GPIO管腳;
MODE:該管腳對應的模式,即該管腳作爲什麼來用的,如作爲普通的GPIO,或者int等,通過mtk_pinmux_get(chip, i)方法獲取;
DIR:輸入還是輸出,即該管腳對應的方向,通過mtk_gpio_get_direction方法獲取;
DOUT:如果是輸出模式對應的值是多少,通過mtk_gpio_get_out方法獲取,默認爲0;
DIN:如果是輸入模式對應的值是多少,通過mtk_gpio_get_in方法獲取,默認爲0;
PULL_EN:是否支持輸入上下拉,通過mtk_pullen_get方法獲取,如果不支持默認爲0;
PULL_SEL:如果支持上下拉,對應的值。通過pull_val的值來決定上拉還是下拉。如果不支持,默認爲0;
IES+SMT:輸入翻轉