ice: add write functionality for GNSS TTY

Add the possibility to write raw bytes to the GNSS module through the
first TTY device. This allows user to configure the module.

Create a second read-only TTY device.
Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Documentation/networking/device_drivers/ethernet/intel/ice.rst

@@ -901,6 +901,15 @@ To enable/disable UDP Segmentation Offload, issue the following command::
 
   # ethtool -K <ethX> tx-udp-segmentation [off|on]
 
+GNSS module
+-----------
+Allows user to read messages from the GNSS module and write supported commands.
+If the module is physically present, driver creates 2 TTYs for each supported
+device in /dev, ttyGNSS_<device>:<function>_0 and _1. First one (_0) is RW and
+the second one is RO.
+The protocol of write commands is dependent on the GNSS module as the driver
+writes raw bytes from the TTY to the GNSS i2c. Please refer to the module
+documentation for details.
 
 Performance Optimization
 ========================

drivers/net/ethernet/intel/ice/ice.h

@@ -545,8 +545,8 @@ struct ice_pf {
 	u32 msg_enable;
 	struct ice_ptp ptp;
 	struct tty_driver *ice_gnss_tty_driver;
-	struct tty_port gnss_tty_port;
-	struct gnss_serial *gnss_serial;
+	struct tty_port *gnss_tty_port[ICE_GNSS_TTY_MINOR_DEVICES];
+	struct gnss_serial *gnss_serial[ICE_GNSS_TTY_MINOR_DEVICES];
 	u16 num_rdma_msix;		/* Total MSIX vectors for RDMA driver */
 	u16 rdma_base_vector;
 

drivers/net/ethernet/intel/ice/ice_gnss.h

 /* SPDX-License-Identifier: GPL-2.0 */
-/* Copyright (C) 2018-2021, Intel Corporation. */
+/* Copyright (C) 2021-2022, Intel Corporation. */
 
 #ifndef _ICE_GNSS_H_
 #define _ICE_GNSS_H_
@@ -8,14 +8,34 @@
 #include <linux/tty_flip.h>
 
 #define ICE_E810T_GNSS_I2C_BUS		0x2
+#define ICE_GNSS_TIMER_DELAY_TIME	(HZ / 10) /* 0.1 second per message */
+/* Create 2 minor devices, both using the same GNSS module. First one is RW,
+ * second one RO.
+ */
+#define ICE_GNSS_TTY_MINOR_DEVICES	2
+#define ICE_GNSS_TTY_WRITE_BUF		250
+#define ICE_MAX_I2C_DATA_SIZE		FIELD_MAX(ICE_AQC_I2C_DATA_SIZE_M)
+#define ICE_MAX_I2C_WRITE_BYTES		4
+
+/* u-blox ZED-F9T specific definitions */
 #define ICE_GNSS_UBX_I2C_BUS_ADDR	0x42
 /* Data length register is big endian */
 #define ICE_GNSS_UBX_DATA_LEN_H		0xFD
 #define ICE_GNSS_UBX_DATA_LEN_WIDTH	2
 #define ICE_GNSS_UBX_EMPTY_DATA		0xFF
-#define ICE_GNSS_TIMER_DELAY_TIME	(HZ / 10) /* 0.1 second per message */
-#define ICE_MAX_I2C_DATA_SIZE		FIELD_MAX(ICE_AQC_I2C_DATA_SIZE_M)
+/* For u-blox writes are performed without address so the first byte to write is
+ * passed as I2C addr parameter.
+ */
+#define ICE_GNSS_UBX_WRITE_BYTES	(ICE_MAX_I2C_WRITE_BYTES + 1)
 #define ICE_MAX_UBX_READ_TRIES		255
+#define ICE_MAX_UBX_ACK_READ_TRIES	4095
+
+struct gnss_write_buf {
+	struct list_head queue;
+	unsigned int size;
+	unsigned char *buf;
+};
+
 
 /**
  * struct gnss_serial - data used to initialize GNSS TTY port
@@ -25,6 +45,8 @@
  * @gnss_mutex: gnss_mutex used to protect GNSS serial operations
  * @kworker: kwork thread for handling periodic work
  * @read_work: read_work function for handling GNSS reads
+ * @write_work: write_work function for handling GNSS writes
+ * @queue: write buffers queue
  */
 struct gnss_serial {
 	struct ice_pf *back;
@@ -33,6 +55,8 @@ struct gnss_serial {
 	struct mutex gnss_mutex; /* protects GNSS serial structure */
 	struct kthread_worker *kworker;
 	struct kthread_delayed_work read_work;
+	struct kthread_work write_work;
+	struct list_head queue;
 };
 
 #if IS_ENABLED(CONFIG_TTY)