spi: spi-fsl-dspi: Implement the PTP system timestamping for TCFQ mode

In this mode, the DSPI controller uses PIO to transfer word by word. In
comparison, in EOQ mode the 4-word deep FIFO is being used, hence the
current logic will need some adaptation for which I do not have the
hardware (Coldfire) to test. It is not clear what is the timing of DMA
transfers and whether timestamping in the driver brings any overall
performance increase compared to regular timestamping done in the core.

Short phc2sys summary after 58 minutes of running on LS1021A-TSN with
interrupts disabled during the critical section:

  offset: min -26251 max 16416 mean -21.8672 std dev 863.416
  delay: min 4720 max 57280 mean 5182.49 std dev 1607.19
  lost servo lock 3 times

Summary of the same phc2sys service running for 120 minutes with
interrupts disabled:

  offset: min -378 max 381 mean -0.0083089 std dev 101.495
  delay: min 4720 max 5920 mean 5129.38 std dev 154.899
  lost servo lock 0 times

The minimum delay (pre to post time) in nanoseconds is the same, but the
maximum delay is quite a bit higher, due to interrupts getting sometimes
executed and interfering with the measurement. Hence set disable_irqs
whenever possible (aka when the driver runs in poll mode - otherwise it
would be a contradiction in terms).

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20190905010114.26718-4-olteanv@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -129,6 +129,7 @@ enum dspi_trans_mode {
 struct fsl_dspi_devtype_data {
 	enum dspi_trans_mode	trans_mode;
 	u8			max_clock_factor;
+	bool			ptp_sts_supported;
 	bool			xspi_mode;
 };
 
@@ -140,12 +141,14 @@ static const struct fsl_dspi_devtype_data vf610_data = {
 static const struct fsl_dspi_devtype_data ls1021a_v1_data = {
 	.trans_mode		= DSPI_TCFQ_MODE,
 	.max_clock_factor	= 8,
+	.ptp_sts_supported	= true,
 	.xspi_mode		= true,
 };
 
 static const struct fsl_dspi_devtype_data ls2085a_data = {
 	.trans_mode		= DSPI_TCFQ_MODE,
 	.max_clock_factor	= 8,
+	.ptp_sts_supported	= true,
 };
 
 static const struct fsl_dspi_devtype_data coldfire_data = {
@@ -654,6 +657,9 @@ static int dspi_rxtx(struct fsl_dspi *dspi)
 	u16 spi_tcnt;
 	u32 spi_tcr;
 
+	spi_take_timestamp_post(dspi->ctlr, dspi->cur_transfer,
+				dspi->tx - dspi->bytes_per_word, !dspi->irq);
+
 	/* Get transfer counter (in number of SPI transfers). It was
 	 * reset to 0 when transfer(s) were started.
 	 */
@@ -672,6 +678,9 @@ static int dspi_rxtx(struct fsl_dspi *dspi)
 		/* Success! */
 		return 0;
 
+	spi_take_timestamp_pre(dspi->ctlr, dspi->cur_transfer,
+			       dspi->tx, !dspi->irq);
+
 	if (trans_mode == DSPI_EOQ_MODE)
 		dspi_eoq_write(dspi);
 	else if (trans_mode == DSPI_TCFQ_MODE)
@@ -779,6 +788,9 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 				     SPI_FRAME_EBITS(transfer->bits_per_word) |
 				     SPI_CTARE_DTCP(1));
 
+		spi_take_timestamp_pre(dspi->ctlr, dspi->cur_transfer,
+				       dspi->tx, !dspi->irq);
+
 		trans_mode = dspi->devtype_data->trans_mode;
 		switch (trans_mode) {
 		case DSPI_EOQ_MODE:
@@ -1155,6 +1167,7 @@ static int dspi_probe(struct platform_device *pdev)
 	init_waitqueue_head(&dspi->waitq);
 
 poll_mode:
+
 	if (dspi->devtype_data->trans_mode == DSPI_DMA_MODE) {
 		ret = dspi_request_dma(dspi, res->start);
 		if (ret < 0) {
@@ -1166,6 +1179,8 @@ poll_mode:
 	ctlr->max_speed_hz =
 		clk_get_rate(dspi->clk) / dspi->devtype_data->max_clock_factor;
 
+	ctlr->ptp_sts_supported = dspi->devtype_data->ptp_sts_supported;
+
 	platform_set_drvdata(pdev, ctlr);
 
 	ret = spi_register_controller(ctlr);