[PATCH v2 23/27] mtd: spinand: Enhance the logic when picking a variant

[Miquel Raynal <miquel.raynal@xxxxxxxxxxx>]

Currently the best variant picked in the first one in the list provided
in the manufacturer driver. This worked well while all operations where
performed at the same speed, but with the introduction of DTR transfers
and per operation maximum frequencies, this no longer works correctly.

Let's continue iterating over all the alternatives, even if we find a
match, keeping a reference over the theoretically fastest
operation. Only at the end we can tell which variant is the best.

This logic happening only once at boot, the extra computing needed
compared to the previous version is acceptable wrt. the expected
improvements.

Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
---
 drivers/mtd/nand/spi/core.c | 13 ++++++++++---
 include/linux/spi/spi-mem.h |  2 +-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
index 94f33c8be031ac60208e22e4e3fa0d90cfae093c..a2a8cfd1752139e3227fa4a39ab0e25bbeec53f8 100644
--- a/drivers/mtd/nand/spi/core.c
+++ b/drivers/mtd/nand/spi/core.c
@@ -1198,10 +1198,13 @@ spinand_select_op_variant(struct spinand_device *spinand,
 			  const struct spinand_op_variants *variants)
 {
 	struct nand_device *nand = spinand_to_nand(spinand);
+	const struct spi_mem_op *best_variant = NULL;
+	u64 best_op_duration_ns = ULLONG_MAX;
 	unsigned int i;
 
 	for (i = 0; i < variants->nops; i++) {
 		struct spi_mem_op op = variants->ops[i];
+		u64 op_duration_ns = 0;
 		unsigned int nbytes;
 		int ret;
 
@@ -1220,13 +1223,17 @@ spinand_select_op_variant(struct spinand_device *spinand,
 				break;
 
 			nbytes -= op.data.nbytes;
+
+			op_duration_ns += spi_mem_calc_op_duration(&op);
 		}
 
-		if (!nbytes)
-			return &variants->ops[i];
+		if (!nbytes && op_duration_ns < best_op_duration_ns) {
+			best_op_duration_ns = op_duration_ns;
+			best_variant = &variants->ops[i];
+		}
 	}
 
-	return NULL;
+	return best_variant;
 }
 
 /**
diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h
index 82390712794c5a4dcef1319c19d74b77b6e1e724..c4830dfaff3db5549c45bb7a9c4bf5110fa2e338 100644
--- a/include/linux/spi/spi-mem.h
+++ b/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 *mem, struct spi_mem_op *op);
+u64 spi_mem_calc_op_duration(struct spi_mem_op *op);
 
 bool spi_mem_supports_op(struct spi_mem *mem,
 			 const struct spi_mem_op *op);

-- 
2.47.0