spi: Don't look at TX buffer for PTP system timestamping

The API for PTP system timestamping (associating a SPI transaction with
the system time at which it was transferred) is flawed: it assumes that
the xfer->tx_buf pointer will always be present.

This is, of course, not always the case.

So introduce a "progress" variable that denotes how many word have been
transferred.

Fix the Freescale DSPI driver, the only user of the API so far, in the
same patch.

Fixes: b42faeee ("spi: Add a PTP system timestamp to the transfer structure")
Fixes: d6b71dfa ("spi: spi-fsl-dspi: Implement the PTP system timestamping for TCFQ mode")
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20191227012417.1057-1-olteanv@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -185,6 +185,7 @@ struct fsl_dspi {
 	struct spi_transfer			*cur_transfer;
 	struct spi_message			*cur_msg;
 	struct chip_data			*cur_chip;
+	size_t					progress;
 	size_t					len;
 	const void				*tx;
 	void					*rx;
@@ -658,7 +659,7 @@ static int dspi_rxtx(struct fsl_dspi *dspi)
 	u32 spi_tcr;
 
 	spi_take_timestamp_post(dspi->ctlr, dspi->cur_transfer,
-				dspi->tx - dspi->bytes_per_word, !dspi->irq);
+				dspi->progress, !dspi->irq);
 
 	/* Get transfer counter (in number of SPI transfers). It was
 	 * reset to 0 when transfer(s) were started.
@@ -667,6 +668,7 @@ static int dspi_rxtx(struct fsl_dspi *dspi)
 	spi_tcnt = SPI_TCR_GET_TCNT(spi_tcr);
 	/* Update total number of bytes that were transferred */
 	msg->actual_length += spi_tcnt * dspi->bytes_per_word;
+	dspi->progress += spi_tcnt;
 
 	trans_mode = dspi->devtype_data->trans_mode;
 	if (trans_mode == DSPI_EOQ_MODE)
@@ -679,7 +681,7 @@ static int dspi_rxtx(struct fsl_dspi *dspi)
 		return 0;
 
 	spi_take_timestamp_pre(dspi->ctlr, dspi->cur_transfer,
-			       dspi->tx, !dspi->irq);
+			       dspi->progress, !dspi->irq);
 
 	if (trans_mode == DSPI_EOQ_MODE)
 		dspi_eoq_write(dspi);
@@ -768,6 +770,7 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 		dspi->rx = transfer->rx_buf;
 		dspi->rx_end = dspi->rx + transfer->len;
 		dspi->len = transfer->len;
+		dspi->progress = 0;
 		/* Validated transfer specific frame size (defaults applied) */
 		dspi->bits_per_word = transfer->bits_per_word;
 		if (transfer->bits_per_word <= 8)
@@ -789,7 +792,7 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 				     SPI_CTARE_DTCP(1));
 
 		spi_take_timestamp_pre(dspi->ctlr, dspi->cur_transfer,
-				       dspi->tx, !dspi->irq);
+				       dspi->progress, !dspi->irq);
 
 		trans_mode = dspi->devtype_data->trans_mode;
 		switch (trans_mode) {

drivers/spi/spi.c

@@ -1499,8 +1499,7 @@ static void spi_pump_messages(struct kthread_work *work)
  *			    advances its @tx buffer pointer monotonically.
  * @ctlr: Pointer to the spi_controller structure of the driver
  * @xfer: Pointer to the transfer being timestamped
- * @tx: Pointer to the current word within the xfer->tx_buf that the driver is
- *	preparing to transmit right now.
+ * @progress: How many words (not bytes) have been transferred so far
  * @irqs_off: If true, will disable IRQs and preemption for the duration of the
  *	      transfer, for less jitter in time measurement. Only compatible
  *	      with PIO drivers. If true, must follow up with
@@ -1510,21 +1509,19 @@ static void spi_pump_messages(struct kthread_work *work)
  */
 void spi_take_timestamp_pre(struct spi_controller *ctlr,
 			    struct spi_transfer *xfer,
-			    const void *tx, bool irqs_off)
+			    size_t progress, bool irqs_off)
 {
-	u8 bytes_per_word = DIV_ROUND_UP(xfer->bits_per_word, 8);
-
 	if (!xfer->ptp_sts)
 		return;
 
 	if (xfer->timestamped_pre)
 		return;
 
-	if (tx < (xfer->tx_buf + xfer->ptp_sts_word_pre * bytes_per_word))
+	if (progress < xfer->ptp_sts_word_pre)
 		return;
 
 	/* Capture the resolution of the timestamp */
-	xfer->ptp_sts_word_pre = (tx - xfer->tx_buf) / bytes_per_word;
+	xfer->ptp_sts_word_pre = progress;
 
 	xfer->timestamped_pre = true;
 
@@ -1546,23 +1543,20 @@ EXPORT_SYMBOL_GPL(spi_take_timestamp_pre);
  *			     timestamped.
  * @ctlr: Pointer to the spi_controller structure of the driver
  * @xfer: Pointer to the transfer being timestamped
- * @tx: Pointer to the current word within the xfer->tx_buf that the driver has
- *	just transmitted.
+ * @progress: How many words (not bytes) have been transferred so far
  * @irqs_off: If true, will re-enable IRQs and preemption for the local CPU.
  */
 void spi_take_timestamp_post(struct spi_controller *ctlr,
 			     struct spi_transfer *xfer,
-			     const void *tx, bool irqs_off)
+			     size_t progress, bool irqs_off)
 {
-	u8 bytes_per_word = DIV_ROUND_UP(xfer->bits_per_word, 8);
-
 	if (!xfer->ptp_sts)
 		return;
 
 	if (xfer->timestamped_post)
 		return;
 
-	if (tx < (xfer->tx_buf + xfer->ptp_sts_word_post * bytes_per_word))
+	if (progress < xfer->ptp_sts_word_post)
 		return;
 
 	ptp_read_system_postts(xfer->ptp_sts);
@@ -1573,7 +1567,7 @@ void spi_take_timestamp_post(struct spi_controller *ctlr,
 	}
 
 	/* Capture the resolution of the timestamp */
-	xfer->ptp_sts_word_post = (tx - xfer->tx_buf) / bytes_per_word;
+	xfer->ptp_sts_word_post = progress;
 
 	xfer->timestamped_post = true;
 }

include/linux/spi/spi.h

@@ -689,10 +689,10 @@ extern void spi_finalize_current_transfer(struct spi_controller *ctlr);
 /* Helper calls for driver to timestamp transfer */
 void spi_take_timestamp_pre(struct spi_controller *ctlr,
 			    struct spi_transfer *xfer,
-			    const void *tx, bool irqs_off);
+			    size_t progress, bool irqs_off);
 void spi_take_timestamp_post(struct spi_controller *ctlr,
 			     struct spi_transfer *xfer,
-			     const void *tx, bool irqs_off);
+			     size_t progress, bool irqs_off);
 
 /* the spi driver core manages memory for the spi_controller classdev */
 extern struct spi_controller *__spi_alloc_controller(struct device *host,