[PATCH v2] spi: spi-mem: add statistics support to ->exec_op() calls

["Théo Lebrun" <theo.lebrun@bootlin.com>]

Current behavior is that spi-mem operations do not increment statistics,
neither per-controller nor per-device, if ->exec_op() is used. For
operations that do NOT use ->exec_op(), stats are increased as the
usual spi_sync() is called.

The newly implemented spi_mem_add_op_stats() function is strongly
inspired by spi_statistics_add_transfer_stats(); locking logic and
l2len computation comes from there.

Statistics that are being filled: bytes{,_rx,_tx}, messages, transfers,
errors, timedout, transfer_bytes_histo_*.

Note about messages & transfers counters: in the fallback to spi_sync()
case, there are from 1 to 4 transfers per message. We only register one
big transfer in the ->exec_op() case as that is closer to reality.

This patch is NOT touching:
 - spi_async, spi_sync, spi_sync_immediate: those counters describe
   precise function calls, incrementing them would be lying. I believe
   comparing the messages counter to spi_async+spi_sync is a good way
   to detect ->exec_op() calls, but I might be missing edge cases
   knowledge.
 - transfers_split_maxsize: splitting cannot happen if ->exec_op() is
   provided.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
Changes in v2:
- Turn len and l2len into u64. Remove casts on all 4 nbytes fields.
  Remove clamp of l2len to be positive.
- Replace "xferred" in comment by "transferred".
- Remove sysfs demo from commit message. Moved to below the tear line.
- Take Reviewed-by Dhruva Gole.
- Link to v1: https://lore.kernel.org/r/20240209-spi-mem-stats-v1-1-dd1a422fc015@bootlin.com
---

Testing this patch:

   $ cd /sys/devices/platform/soc
   $ find . -type d -path "*spi*" -name statistics
   ./2100000.spi/spi_master/spi0/statistics
   ./2100000.spi/spi_master/spi0/spi0.0/statistics
   $ cd ./2100000.spi/spi_master/spi0/statistics

   $ for f in *; do printf "%s\t" $f; cat $f; done | \
         grep -v transfer_bytes_histo | column -t
   bytes                    240745444
   bytes_rx                 240170907
   bytes_tx                 126320
   errors                   0
   messages                 97354
   spi_async                0
   spi_sync                 0
   spi_sync_immediate       0
   timedout                 0
   transfers                97354
   transfers_split_maxsize  0
---
 drivers/spi/spi-mem.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index 2dc8ceb85374..c9d6d42a88f5 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -297,6 +297,49 @@ static void spi_mem_access_end(struct spi_mem *mem)
 		pm_runtime_put(ctlr->dev.parent);
 }
 
+static void spi_mem_add_op_stats(struct spi_statistics __percpu *pcpu_stats,
+				 const struct spi_mem_op *op, int exec_op_ret)
+{
+	struct spi_statistics *stats;
+	u64 len, l2len;
+
+	get_cpu();
+	stats = this_cpu_ptr(pcpu_stats);
+	u64_stats_update_begin(&stats->syncp);
+
+	/*
+	 * We do not have the concept of messages or transfers. Let's consider
+	 * that one operation is equivalent to one message and one transfer.
+	 */
+	u64_stats_inc(&stats->messages);
+	u64_stats_inc(&stats->transfers);
+
+	/* Use the sum of all lengths as bytes count and histogram value. */
+	len = op->cmd.nbytes + op->addr.nbytes;
+	len += op->dummy.nbytes + op->data.nbytes;
+	u64_stats_add(&stats->bytes, len);
+	l2len = min(fls(len), SPI_STATISTICS_HISTO_SIZE) - 1;
+	u64_stats_inc(&stats->transfer_bytes_histo[l2len]);
+
+	/* Only account for data bytes as transferred bytes. */
+	if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_OUT)
+		u64_stats_add(&stats->bytes_tx, op->data.nbytes);
+	if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_IN)
+		u64_stats_add(&stats->bytes_rx, op->data.nbytes);
+
+	/*
+	 * A timeout is not an error, following the same behavior as
+	 * spi_transfer_one_message().
+	 */
+	if (exec_op_ret == -ETIMEDOUT)
+		u64_stats_inc(&stats->timedout);
+	else if (exec_op_ret)
+		u64_stats_inc(&stats->errors);
+
+	u64_stats_update_end(&stats->syncp);
+	put_cpu();
+}
+
 /**
  * spi_mem_exec_op() - Execute a memory operation
  * @mem: the SPI memory
@@ -339,8 +382,12 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 		 * read path) and expect the core to use the regular SPI
 		 * interface in other cases.
 		 */
-		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP)
+		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP) {
+			spi_mem_add_op_stats(ctlr->pcpu_statistics, op, ret);
+			spi_mem_add_op_stats(mem->spi->pcpu_statistics, op, ret);
+
 			return ret;
+		}
 	}
 
 	tmpbufsize = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;

---
base-commit: 19b50f80b3a4865bd477aa5c026dd234d39a50d2
change-id: 20240209-spi-mem-stats-ff9bf91c0f7e

Best regards,
-- 
Théo Lebrun <theo.lebrun@bootlin.com>