spi: spi-mem: add spi_mem_dtr_supports_op()

spi_mem_default_supports_op() rejects DTR ops by default to ensure that
the controller drivers that haven't been updated with DTR support
continue to reject them. It also makes sure that controllers that don't
support DTR mode at all (which is most of them at the moment) also
reject them.

This means that controller drivers that want to support DTR mode can't
use spi_mem_default_supports_op(). Driver authors have to roll their own
supports_op() function and mimic the buswidth checks. See
spi-cadence-quadspi.c for example. Or even worse, driver authors might
skip it completely or get it wrong.

Add spi_mem_dtr_supports_op(). It provides a basic sanity check for DTR
ops and performs the buswidth requirement check. Move the logic for
checking buswidth in spi_mem_default_supports_op() to a separate
function so the logic is not repeated twice.
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20210204141218.32229-1-p.yadav@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-mem.c

@@ -137,8 +137,8 @@ static int spi_check_buswidth_req(struct spi_mem *mem, u8 buswidth, bool tx)
 	return -ENOTSUPP;
 }
 
-bool spi_mem_default_supports_op(struct spi_mem *mem,
-				 const struct spi_mem_op *op)
+static bool spi_mem_check_buswidth(struct spi_mem *mem,
+				   const struct spi_mem_op *op)
 {
 	if (spi_check_buswidth_req(mem, op->cmd.buswidth, true))
 		return false;
@@ -156,13 +156,29 @@ bool spi_mem_default_supports_op(struct spi_mem *mem,
 				   op->data.dir == SPI_MEM_DATA_OUT))
 		return false;
 
+	return true;
+}
+
+bool spi_mem_dtr_supports_op(struct spi_mem *mem,
+			     const struct spi_mem_op *op)
+{
+	if (op->cmd.nbytes != 2)
+		return false;
+
+	return spi_mem_check_buswidth(mem, op);
+}
+EXPORT_SYMBOL_GPL(spi_mem_dtr_supports_op);
+
+bool spi_mem_default_supports_op(struct spi_mem *mem,
+				 const struct spi_mem_op *op)
+{
 	if (op->cmd.dtr || op->addr.dtr || op->dummy.dtr || op->data.dtr)
 		return false;
 
 	if (op->cmd.nbytes != 1)
 		return false;
 
-	return true;
+	return spi_mem_check_buswidth(mem, op);
 }
 EXPORT_SYMBOL_GPL(spi_mem_default_supports_op);
 

include/linux/spi/spi-mem.h

@@ -311,6 +311,9 @@ void spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
 bool spi_mem_default_supports_op(struct spi_mem *mem,
 				 const struct spi_mem_op *op);
 
+bool spi_mem_dtr_supports_op(struct spi_mem *mem,
+			     const struct spi_mem_op *op);
+
 #else
 static inline int
 spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
@@ -334,6 +337,12 @@ bool spi_mem_default_supports_op(struct spi_mem *mem,
 	return false;
 }
 
+static inline
+bool spi_mem_dtr_supports_op(struct spi_mem *mem,
+			     const struct spi_mem_op *op)
+{
+	return false;
+}
 #endif /* CONFIG_SPI_MEM */
 
 int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op);