ptp: ocp: Add firmware capability bits for feature gating

Add the ability to group sysfs nodes behind a firmware feature
check.  This way non-present sysfs attributes are omitted on
older firmware, which does not have newer features.

This will be used in the upcoming patches which adds more
features to the timecard.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_ocp.c

@@ -218,6 +218,13 @@ struct ptp_ocp_sma_connector {
 	bool	disabled;
 };
 
+struct ocp_attr_group {
+	u64 cap;
+	const struct attribute_group *group;
+};
+
+#define OCP_CAP_BASIC	BIT(0)
+
 #define OCP_BOARD_ID_LEN		13
 #define OCP_SERIAL_LEN			6
 
@@ -248,6 +255,7 @@ struct ptp_ocp {
 	struct platform_device	*spi_flash;
 	struct clk_hw		*i2c_clk;
 	struct timer_list	watchdog;
+	const struct ocp_attr_group *attr_tbl;
 	const struct ptp_ocp_eeprom_map *eeprom_map;
 	struct dentry		*debug_root;
 	time64_t		gnss_lost;
@@ -265,6 +273,7 @@ struct ptp_ocp {
 	int			flash_start;
 	u32			utc_tai_offset;
 	u32			ts_window_adjust;
+	u64			fw_cap;
 	struct ptp_ocp_sma_connector sma[4];
 };
 
@@ -290,6 +299,8 @@ static int ptp_ocp_fb_board_init(struct ptp_ocp *bp, struct ocp_resource *r);
 static irqreturn_t ptp_ocp_ts_irq(int irq, void *priv);
 static int ptp_ocp_ts_enable(void *priv, u32 req, bool enable);
 
+static const struct ocp_attr_group fb_timecard_groups[];
+
 struct ptp_ocp_eeprom_map {
 	u16	off;
 	u16	len;
@@ -1526,6 +1537,8 @@ ptp_ocp_fb_board_init(struct ptp_ocp *bp, struct ocp_resource *r)
 	bp->flash_start = 1024 * 4096;
 	bp->eeprom_map = fb_eeprom_map;
 	bp->fw_version = ioread32(&bp->image->version);
+	bp->attr_tbl = fb_timecard_groups;
+	bp->fw_cap = OCP_CAP_BASIC;
 
 	ptp_ocp_tod_init(bp);
 	ptp_ocp_nmea_out_init(bp);
@@ -2167,7 +2180,7 @@ tod_correction_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(tod_correction);
 
-static struct attribute *timecard_attrs[] = {
+static struct attribute *fb_timecard_attrs[] = {
 	&dev_attr_serialnum.attr,
 	&dev_attr_gnss_sync.attr,
 	&dev_attr_clock_source.attr,
@@ -2186,7 +2199,13 @@ static struct attribute *timecard_attrs[] = {
 	&dev_attr_tod_correction.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(timecard);
+static const struct attribute_group fb_timecard_group = {
+	.attrs = fb_timecard_attrs,
+};
+static const struct ocp_attr_group fb_timecard_groups[] = {
+	{ .cap = OCP_CAP_BASIC,	    .group = &fb_timecard_group },
+	{ },
+};
 
 static void
 gpio_input_map(char *buf, struct ptp_ocp *bp, u16 map[][2], u16 bit,
@@ -2605,6 +2624,7 @@ ptp_ocp_complete(struct ptp_ocp *bp)
 {
 	struct pps_device *pps;
 	char buf[32];
+	int i, err;
 
 	if (bp->gnss_port != -1) {
 		sprintf(buf, "ttyS%d", bp->gnss_port);
@@ -2629,8 +2649,13 @@ ptp_ocp_complete(struct ptp_ocp *bp)
 	if (pps)
 		ptp_ocp_symlink(bp, pps->dev, "pps");
 
-	if (device_add_groups(&bp->dev, timecard_groups))
-		pr_err("device add groups failed\n");
+	for (i = 0; bp->attr_tbl[i].cap; i++) {
+		if (!(bp->attr_tbl[i].cap & bp->fw_cap))
+			continue;
+		err = sysfs_create_group(&bp->dev.kobj, bp->attr_tbl[i].group);
+		if (err)
+			return err;
+	}
 
 	ptp_ocp_debugfs_add_device(bp);
 
@@ -2703,12 +2728,15 @@ static void
 ptp_ocp_detach_sysfs(struct ptp_ocp *bp)
 {
 	struct device *dev = &bp->dev;
+	int i;
 
 	sysfs_remove_link(&dev->kobj, "ttyGNSS");
 	sysfs_remove_link(&dev->kobj, "ttyMAC");
 	sysfs_remove_link(&dev->kobj, "ptp");
 	sysfs_remove_link(&dev->kobj, "pps");
-	device_remove_groups(dev, timecard_groups);
+	if (bp->attr_tbl)
+		for (i = 0; bp->attr_tbl[i].cap; i++)
+			sysfs_remove_group(&dev->kobj, bp->attr_tbl[i].group);
 }
 
 static void