@@ -562,6 +562,36 @@ void spi_mem_adjust_op_freq(struct spi_mem *mem, struct spi_mem_op *op)
}
EXPORT_SYMBOL_GPL(spi_mem_adjust_op_freq);
+/**
+ * spi_mem_calc_op_duration() - Derives the theoretical length (in ns) of an
+ * operation. This helps finding the best variant
+ * among a list of possible choices.
+ * @op: the operation to benchmark
+ *
+ * Some chips have per-op frequency limitations, PCBs usually have their own
+ * limitations as well, and controllers can support dual, quad or even octal
+ * modes, sometimes in DTR. All these combinations make it impossible to
+ * statically list the best combination for all situations. If we want something
+ * 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.
+ */
+u64 spi_mem_calc_op_duration(struct spi_mem_op *op)
+{
+ u64 ncycles = 0;
+ u32 ns_per_cycles;
+
+ ns_per_cycles = 1000000000 / op->max_freq;
+ 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);
+ ncycles += ((op->dummy.nbytes * 8) / op->dummy.buswidth) / (op->dummy.dtr ? 2 : 1);
+ ncycles += ((op->data.nbytes * 8) / op->data.buswidth) / (op->data.dtr ? 2 : 1);
+
+ return ncycles * ns_per_cycles;
+}
+EXPORT_SYMBOL_GPL(spi_mem_calc_op_duration);
+
static ssize_t spi_mem_no_dirmap_read(struct spi_mem_dirmap_desc *desc,
u64 offs, size_t len, void *buf)
{
@@ -424,6 +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);
bool spi_mem_supports_op(struct spi_mem *mem,
const struct spi_mem_op *op);
In the SPI-NAND layer, we currently make list of operation variants from the fastest one to the slowest and there is a bit of logic in the core to go over them and pick the first one that is supported by the controller, ie. the fastest one among the supported ops. This kind of logic only works if all operations run at the same frequency, but as soon as we introduce per operation max frequencies it is not longer as obvious which operation will be faster, especially since it also depends on the PCB/controller frequency limitation. One way to make this choice more clever is to go over all the variants and for each of them derive an indicator which will help derive the theoretical best. In this case, we derive a theoretical duration for the entire operation and we take the smallest one. Add a helper that parses the spi-mem operation and returns this value. Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> --- drivers/spi/spi-mem.c | 30 ++++++++++++++++++++++++++++++ include/linux/spi/spi-mem.h | 1 + 2 files changed, 31 insertions(+)