drivers: net: cpsw: Add support to drive gpios for ethernet to be functional

In DRA72x EVM, by default slave 1 is connected to the onboard
phy, but slave 2 pins are also muxed with video input module
which is controlled by pcf857x gpio and currently to select slave
0 to connect to phy gpio hogging is used, but with
omap2plus_defconfig the pcf857x gpio is built as module. So when
using NFS on DRA72x EVM, board doesn't boot as gpio hogging do
not set proper gpio state to connect slave 0 to phy as it is
built as module and you do not see any errors for not setting
gpio and just mentions dhcp reply not got.

To solve this issue, introducing "mode-gpios" in DT when gpio
based muxing is required. This will throw a warning when gpio
get fails and returns probe defer. When gpio-pcf857x module is
installed, cpsw probes again and ethernet becomes functional.
Verified this on DRA72x with pcf as module and ramdisk.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/cpsw.txt

@@ -30,6 +30,13 @@ Optional properties:
 - dual_emac		: Specifies Switch to act as Dual EMAC
 - syscon		: Phandle to the system control device node, which is
 			  the control module device of the am33x
+- mode-gpios		: Should be added if one/multiple gpio lines are
+			  required to be driven so that cpsw data lines
+			  can be connected to the phy via selective mux.
+			  For example in dra72x-evm, pcf gpio has to be
+			  driven low so that cpsw slave 0 and phy data
+			  lines are connected via mux.
+
 
 Slave Properties:
 Required properties:

drivers/net/ethernet/ti/cpsw.c

@@ -29,6 +29,7 @@
 #include <linux/workqueue.h>
 #include <linux/delay.h>
 #include <linux/pm_runtime.h>
+#include <linux/gpio.h>
 #include <linux/of.h>
 #include <linux/of_net.h>
 #include <linux/of_device.h>
@@ -2207,6 +2208,7 @@ static int cpsw_probe(struct platform_device *pdev)
 	void __iomem			*ss_regs;
 	struct resource			*res, *ss_res;
 	const struct of_device_id	*of_id;
+	struct gpio_descs		*mode;
 	u32 slave_offset, sliver_offset, slave_size;
 	int ret = 0, i;
 	int irq;
@@ -2232,6 +2234,13 @@ static int cpsw_probe(struct platform_device *pdev)
 		goto clean_ndev_ret;
 	}
 
+	mode = devm_gpiod_get_array_optional(&pdev->dev, "mode", GPIOD_OUT_LOW);
+	if (IS_ERR(mode)) {
+		ret = PTR_ERR(mode);
+		dev_err(&pdev->dev, "gpio request failed, ret %d\n", ret);
+		goto clean_ndev_ret;
+	}
+
 	/*
 	 * This may be required here for child devices.
 	 */