spi: spi-mem: Take into account the actual maximum frequency

In order to pick the best variant, the duration of each typical
operation is derived and then compared. These durations are based on the
maximum capabilities of the chips, which are commonly the limiting
factors. However there are other possible limiting pieces, such as the
hardware layout, EMC considerations and in some cases, the SPI controller
itself.

We need to take this into account to further refine our variant choice,
so let's use the actual frequency that will be used for the operation
instead of the theoretical maximum.

Signed-off-by: Miquel Raynal <[email protected]>
Reviewed-by: Mark Brown <[email protected]>

Author: miquelraynal

drivers/mtd/nand/spi/core.c

@@ -1297,7 +1297,7 @@ spinand_select_op_variant(struct spinand_device *spinand,
 
 			nbytes -= op.data.nbytes;
 
-			op_duration_ns += spi_mem_calc_op_duration(&op);
+			op_duration_ns += spi_mem_calc_op_duration(spinand->spimem, &op);
 		}
 
 		if (!nbytes && op_duration_ns < best_op_duration_ns) {

drivers/spi/spi-mem.c

@@ -586,15 +586,25 @@ EXPORT_SYMBOL_GPL(spi_mem_adjust_op_freq);
  * accurate, all these combinations should be rated (eg. with a time estimate)
  * and the best pick should be taken based on these calculations.
  *
- * Returns a ns estimate for the time this op would take.
+ * Returns a ns estimate for the time this op would take, except if no
+ * frequency limit has been set, in this case we return the number of
+ * cycles nevertheless to allow callers to distinguish which operation
+ * would be the fastest at iso-frequency.
  */
-u64 spi_mem_calc_op_duration(struct spi_mem_op *op)
+u64 spi_mem_calc_op_duration(struct spi_mem *mem, struct spi_mem_op *op)
 {
 	u64 ncycles = 0;
 	u64 ps_per_cycles, duration;
 
-	ps_per_cycles = 1000000000000ULL;
-	do_div(ps_per_cycles, op->max_freq);
+	spi_mem_adjust_op_freq(mem, op);
+
+	if (op->max_freq) {
+		ps_per_cycles = 1000000000000ULL;
+		do_div(ps_per_cycles, op->max_freq);
+	} else {
+		/* In this case, the unit is no longer a time unit */
+		ps_per_cycles = 1;
+	}
 
 	ncycles += ((op->cmd.nbytes * 8) / op->cmd.buswidth) / (op->cmd.dtr ? 2 : 1);
 	ncycles += ((op->addr.nbytes * 8) / op->addr.buswidth) / (op->addr.dtr ? 2 : 1);

include/linux/spi/spi-mem.h

@@ -424,7 +424,7 @@ bool spi_mem_default_supports_op(struct spi_mem *mem,
 
 int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op);
 void spi_mem_adjust_op_freq(struct spi_mem *mem, struct spi_mem_op *op);
-u64 spi_mem_calc_op_duration(struct spi_mem_op *op);
+u64 spi_mem_calc_op_duration(struct spi_mem *mem, struct spi_mem_op *op);
 
 bool spi_mem_supports_op(struct spi_mem *mem,
 			 const struct spi_mem_op *op);