Subject: [RFC PATCH v2 net-next 01/15] net: dsa: sja1105: Change the PTP command access pattern

From: Vladimir Oltean <[email-masked]>
Date: Fri, 30 Aug 2019 03:46:21 +0300

The PTP command register contains enable bits for:
- Putting the 64-bit PTPCLKVAL register in add/subtract or write mode
- Taking timestamps off of the corrected vs free-running clock
- Starting/stopping the TTEthernet scheduling
- Starting/stopping PPS output
- Resetting the switch

When a command needs to be issued (e.g. "change the PTPCLKVAL from write
mode to add/subtract mode"), one cannot simply write to the command
register setting the PTPCLKADD bit to 1, because that would zeroize the
other settings. One also cannot do a read-modify-write (that would be
too easy for this hardware) because not all bits of the command register
are readable over SPI.

So this leaves us with the only option of keeping the value of the PTP
command register in the driver, and operating on that.

Signed-off-by: Vladimir Oltean <[email-masked]>
---
 drivers/net/dsa/sja1105/sja1105.h     | 5 +++++
 drivers/net/dsa/sja1105/sja1105_ptp.c | 6 +-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/dsa/sja1105/sja1105.h b/drivers/net/dsa/sja1105/sja1105.h
index 78094db32622..d8a92646e80a 100644
--- a/drivers/net/dsa/sja1105/sja1105.h
+++ b/drivers/net/dsa/sja1105/sja1105.h
@@ -50,6 +50,10 @@ struct sja1105_regs {
 	u64 qlevel[SJA1105_NUM_PORTS];
 };
 
+struct sja1105_ptp_cmd {
+	u64 resptp;		/* reset */
+};
+
 struct sja1105_info {
 	u64 device_id;
 	/* Needed for distinction between P and R, and between Q and S
@@ -89,6 +93,7 @@ struct sja1105_private {
 	struct spi_device *spidev;
 	struct dsa_switch *ds;
 	struct sja1105_port ports[SJA1105_NUM_PORTS];
+	struct sja1105_ptp_cmd ptp_cmd;
 	struct ptp_clock_info ptp_caps;
 	struct ptp_clock *clock;
 	/* The cycle counter translates the PTP timestamps (based on
diff --git a/drivers/net/dsa/sja1105/sja1105_ptp.c b/drivers/net/dsa/sja1105/sja1105_ptp.c
index d8e8dd59f3d1..07374ba6b9be 100644
--- a/drivers/net/dsa/sja1105/sja1105_ptp.c
+++ b/drivers/net/dsa/sja1105/sja1105_ptp.c
@@ -54,10 +54,6 @@
 #define cc_to_sja1105(d) container_of((d), struct sja1105_private, tstamp_cc)
 #define dw_to_sja1105(d) container_of((d), struct sja1105_private, refresh_work)
 
-struct sja1105_ptp_cmd {
-	u64 resptp;       /* reset */
-};
-
 int sja1105_get_ts_info(struct dsa_switch *ds, int port,
 			struct ethtool_ts_info *info)
 {
@@ -218,8 +214,8 @@ int sja1105_ptpegr_ts_poll(struct sja1105_private *priv, int port, u64 *ts)
 
 int sja1105_ptp_reset(struct sja1105_private *priv)
 {
+	struct sja1105_ptp_cmd cmd = priv->ptp_cmd;
 	struct dsa_switch *ds = priv->ds;
-	struct sja1105_ptp_cmd cmd = {0};
 	int rc;
 
 	mutex_lock(&priv->ptp_lock);
-- 
2.17.1