[PATCH v2] ptp: ocp: add I2C ISP support for ADVA TimeCard CPLD

[Sagi Maimon <maimon.sagi@gmail.com>]

The ADVA TimeCard programs its on-board CPLD (Lattice MachXO3)
via I2C using in-system programming (ISP).

The CPLD resides on a secondary I2C bus controlled by the
embedded MicroBlaze. To allow programming, the driver must
take ownership of this bus and expose it to userspace.

Add support to:
  - enable the i2c-dev interface to expose /dev/i2c-N
  - provide sysfs control over the secondary I2C bus

Signed-off-by: Sagi Maimon <maimon.sagi@gmail.com>
---
 Address comments from:
  - Andrew Lunn: https://www.spinics.net/lists/netdev/msg1200997.html

 Changes since v1:
  - Add reasoning to the commit message
 
 
 drivers/ptp/ptp_ocp.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
index 35e911f1ad78..1b4ccb4feca5 100644
--- a/drivers/ptp/ptp_ocp.c
+++ b/drivers/ptp/ptp_ocp.c
@@ -4224,6 +4224,34 @@ static const struct ocp_attr_group art_timecard_groups[] = {
 	{ },
 };
 
+static ssize_t
+i2c_bus_ctrl_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct ptp_ocp *bp = dev_get_drvdata(dev);
+
+	if (!bp->pps_select)
+		return -ENODEV;
+	return sysfs_emit(buf, "0x%08x\n",
+			  ioread32(&bp->pps_select->__pad1));
+}
+
+static ssize_t
+i2c_bus_ctrl_store(struct device *dev, struct device_attribute *attr,
+		   const char *buf, size_t count)
+{
+	struct ptp_ocp *bp = dev_get_drvdata(dev);
+	u32 val;
+
+	if (!bp->pps_select)
+		return -ENODEV;
+	if (kstrtou32(buf, 0, &val))
+		return -EINVAL;
+	iowrite32(val, &bp->pps_select->__pad1);
+	return count;
+}
+
+static DEVICE_ATTR_RW(i2c_bus_ctrl);
+
 static struct attribute *adva_timecard_attrs[] = {
 	&dev_attr_serialnum.attr,
 	&dev_attr_gnss_sync.attr,
@@ -4272,6 +4300,7 @@ static struct attribute *adva_timecard_x1_attrs[] = {
 	&dev_attr_ts_window_adjust.attr,
 	&dev_attr_utc_tai_offset.attr,
 	&dev_attr_tod_correction.attr,
+	&dev_attr_i2c_bus_ctrl.attr,
 	NULL,
 };
 
@@ -5235,6 +5264,7 @@ ptp_ocp_init(void)
 	const char *what;
 	int err;
 
+	request_module("i2c-dev");
 	ptp_ocp_debugfs_init();
 
 	what = "timecard class";
-- 
2.47.0