[PATCH v3 1/2] ath6kl_sdio: Add reset gpio module parameter for CHIP_PWD_L pin

[Steve deRosier <derosier@gmail.com>]

Many ath6k chips have a reset pin, usually labeled CHIP_PWD_L. This pin can
be pulled low by the host processor to hold the wifi chip in reset. By
holding the chip in reset, the lowest power consumption available can be
achieved.

This adds a module parameter so the ath6kl_sdio driver can control the
CHIP_PWD_L pin if the implementer so desires. This code is only available
if GPIOLIB is configured.

Signed-off-by: Steve deRosier <steve.derosier@lairdtech.com>
---
 drivers/net/wireless/ath/ath6kl/sdio.c | 70 +++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath6kl/sdio.c b/drivers/net/wireless/ath/ath6kl/sdio.c
index eab0ab9..d06aa41 100644
--- a/drivers/net/wireless/ath/ath6kl/sdio.c
+++ b/drivers/net/wireless/ath/ath6kl/sdio.c
@@ -23,6 +23,7 @@
 #include <linux/mmc/sdio_ids.h>
 #include <linux/mmc/sdio.h>
 #include <linux/mmc/sd.h>
+#include <linux/gpio.h>
 #include "hif.h"
 #include "hif-ops.h"
 #include "target.h"
@@ -69,6 +70,20 @@ struct ath6kl_sdio {
 	spinlock_t wr_async_lock;
 };
 
+/* Delay to avoid the mmc driver calling the probe on the prior notice of
+ * the chip, which we just killed. If this is missing, it results in a
+ * spurious warning:
+ * "ath6kl_sdio: probe of mmc0:0001:1 failed with error -110"
+ *
+ * Time chosen experimentally, with padding
+ */
+#define ATH6KL_MMC_PROBE_DELAY	150
+static unsigned int reset_pwd_gpio = ARCH_NR_GPIOS;
+#ifdef CONFIG_GPIOLIB
+module_param(reset_pwd_gpio, uint, 0644);
+MODULE_PARM_DESC(reset_pwd_gpio, "WIFI CHIP_PWD reset pin GPIO");
+#endif
+
 #define CMD53_ARG_READ          0
 #define CMD53_ARG_WRITE         1
 #define CMD53_ARG_BLOCK_BASIS   1
@@ -1414,20 +1429,73 @@ static struct sdio_driver ath6kl_sdio_driver = {
 	.drv.pm = ATH6KL_SDIO_PM_OPS,
 };
 
+static int ath6kl_sdio_init_gpio(void)
+{
+	int ret = 0;
+
+	if (gpio_is_valid(reset_pwd_gpio)) {
+		/* Request the reset GPIO, and assert it to make sure we get a
+		 * clean boot in-case we had a floating input or other issue.
+		 */
+		ret = gpio_request_one(reset_pwd_gpio,
+				       GPIOF_OUT_INIT_LOW |
+				       GPIOF_EXPORT_DIR_FIXED,
+				       "WIFI_RESET");
+		if (ret) {
+			ath6kl_err("Unable to get WIFI power gpio: %d\n", ret);
+			return ret;
+		}
+
+		ath6kl_dbg(ATH6KL_DBG_SUSPEND, "Setup wifi gpio #%d\n",
+			   reset_pwd_gpio);
+		usleep_range(20, 50); /* Pin must be asserted at least 5 usec */
+		gpio_set_value(reset_pwd_gpio, 1); /* De-assert the pin */
+
+		msleep(ATH6KL_MMC_PROBE_DELAY);
+	}
+
+	return 0;
+}
+
+static void ath6kl_sdio_release_gpio(void)
+{
+	if (gpio_is_valid(reset_pwd_gpio)) {
+		/* Be sure we leave the chip in reset when we unload and also
+		 * release the GPIO
+		 */
+		gpio_set_value(reset_pwd_gpio, 0);
+		gpio_free(reset_pwd_gpio);
+	}
+}
+
 static int __init ath6kl_sdio_init(void)
 {
 	int ret;
 
-	ret = sdio_register_driver(&ath6kl_sdio_driver);
+	ret = ath6kl_sdio_init_gpio();
 	if (ret)
+		goto err_gpio;
+
+	ret = sdio_register_driver(&ath6kl_sdio_driver);
+	if (ret) {
 		ath6kl_err("sdio driver registration failed: %d\n", ret);
+		goto err_register;
+	}
 
 	return ret;
+
+err_register:
+	ath6kl_sdio_release_gpio();
+
+err_gpio:
+	return ret;
 }
 
 static void __exit ath6kl_sdio_exit(void)
 {
 	sdio_unregister_driver(&ath6kl_sdio_driver);
+
+	ath6kl_sdio_release_gpio();
 }
 
 module_init(ath6kl_sdio_init);
-- 
1.9.1