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: b42faeee718c ("spi: Add a PTP system timestamp to the transfer structure")
Fixes: d6b71dfaeeba ("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.com
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 8 insertions, 14 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 0d40953b463c..6b95cd957ba7 100644
--- a/drivers/spi/spi.c
+++ b/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;
 }