i2c: iop: Use GPIO descriptors

The IOP3xx has some elaborate code to directly slam the
GPIO lines multiplexed with I2C down low before enablement,
apparently a workaround for a hardware bug found in the
early chips.

After consulting the developer documentation for IOP80321
and IOP80331 I can clearly see that this may be useful for
IOP80321 family (mach-iop32x) but it is highly dubious for
any 80331 series or later chip: in these chips the lines
are not multiplexed for UARTs.

We convert the code to pass optional GPIO descriptors
and register these only on the 80321-based boards where
it makes sense, optionally obtain them in the driver and
use the gpiod_set_raw_value() to ascertain the line gets
driven low when needed.

The GPIO driver does not give the GPIO chip a reasonable
label so the patch also adds that so that these machine
descriptor tables can be used.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-iop3xx.c

@@ -38,7 +38,7 @@
 #include <linux/platform_device.h>
 #include <linux/i2c.h>
 #include <linux/io.h>
-#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
 
 #include "i2c-iop3xx.h"
 
@@ -71,17 +71,16 @@ iop3xx_i2c_enable(struct i2c_algo_iop3xx_data *iop3xx_adap)
 
 	/*
 	 * Every time unit enable is asserted, GPOD needs to be cleared
-	 * on IOP3XX to avoid data corruption on the bus.
+	 * on IOP3XX to avoid data corruption on the bus. We use the
+	 * gpiod_set_raw_value() to make sure the 0 hits the hardware
+	 * GPOD register. These descriptors are only passed along to
+	 * the device if this is necessary.
 	 */
-#if defined(CONFIG_ARCH_IOP32X) || defined(CONFIG_ARCH_IOP33X)
-	if (iop3xx_adap->id == 0) {
-		gpio_set_value(7, 0);
-		gpio_set_value(6, 0);
-	} else {
-		gpio_set_value(5, 0);
-		gpio_set_value(4, 0);
-	}
-#endif
+	if (iop3xx_adap->gpio_scl)
+		gpiod_set_raw_value(iop3xx_adap->gpio_scl, 0);
+	if (iop3xx_adap->gpio_sda)
+		gpiod_set_raw_value(iop3xx_adap->gpio_sda, 0);
+
 	/* NB SR bits not same position as CR IE bits :-( */
 	iop3xx_adap->SR_enabled =
 		IOP3XX_ISR_ALD | IOP3XX_ISR_BERRD |
@@ -434,6 +433,17 @@ iop3xx_i2c_probe(struct platform_device *pdev)
 		goto free_adapter;
 	}
 
+	adapter_data->gpio_scl = devm_gpiod_get_optional(&pdev->dev,
+							 "scl",
+							 GPIOD_ASIS);
+	if (IS_ERR(adapter_data->gpio_scl))
+		return PTR_ERR(adapter_data->gpio_scl);
+	adapter_data->gpio_sda = devm_gpiod_get_optional(&pdev->dev,
+							 "sda",
+							 GPIOD_ASIS);
+	if (IS_ERR(adapter_data->gpio_sda))
+		return PTR_ERR(adapter_data->gpio_sda);
+
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!res) {
 		ret = -ENODEV;

drivers/i2c/busses/i2c-iop3xx.h

@@ -98,6 +98,8 @@ struct i2c_algo_iop3xx_data {
 	spinlock_t lock;
 	u32 SR_enabled, SR_received;
 	int id;
+	struct gpio_desc *gpio_scl;
+	struct gpio_desc *gpio_sda;
 };
 
 #endif /* I2C_IOP3XX_H */