spi: spi-mem: Allow controller supporting mem_ops without exec_op

Currently exec_op is always required if controller driver provides
mem_ops. But some controller such as bcm63xx-hsspi may only need to
implement other operation like supports_op and use the default
execution operation. This patch removes this restriction.
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20230209200246.141520-13-william.zhang@broadcom.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-mem.c

@@ -325,7 +325,7 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 	if (!spi_mem_internal_supports_op(mem, op))
 		return -ENOTSUPP;
 
-	if (ctlr->mem_ops && !mem->spi->cs_gpiod) {
+	if (ctlr->mem_ops && ctlr->mem_ops->exec_op && !mem->spi->cs_gpiod) {
 		ret = spi_mem_access_start(mem);
 		if (ret)
 			return ret;

drivers/spi/spi.c

@@ -3072,15 +3072,14 @@ static int spi_controller_check_ops(struct spi_controller *ctlr)
 	 * The controller may implement only the high-level SPI-memory like
 	 * operations if it does not support regular SPI transfers, and this is
 	 * valid use case.
-	 * If ->mem_ops is NULL, we request that at least one of the
-	 * ->transfer_xxx() method be implemented.
+	 * If ->mem_ops or ->mem_ops->exec_op is NULL, we request that at least
+	 * one of the ->transfer_xxx() method be implemented.
 	 */
-	if (ctlr->mem_ops) {
-		if (!ctlr->mem_ops->exec_op)
-			return -EINVAL;
-	} else if (!ctlr->transfer && !ctlr->transfer_one &&
+	if (!ctlr->mem_ops || (ctlr->mem_ops && !ctlr->mem_ops->exec_op)) {
+		if (!ctlr->transfer && !ctlr->transfer_one &&
 		   !ctlr->transfer_one_message) {
-		return -EINVAL;
+			return -EINVAL;
+		}
 	}
 
 	return 0;