spi: Make support for regular transfers optional when ->mem_ops != NULL

Some SPI/QuadSPI controllers only expose a high-level SPI memory
interface, thus preventing any regular SPI transfers from being done.

In that case, SPI controller drivers can leave all ->transfer_xxx()
hooks empty and only implement the spi_mem_ops interface.

Adjust the core to allow such situations:
- extend spi_controller_check_ops() to accept situations where all
  ->transfer_xxx() pointers are NULL only if ->mem_ops != NULL
- make sure we do not initialize the SPI message queue if
  ctlr->transfer_one and ctlr->transfer_one_message are missing
- return -ENOTSUPP if someone tries to do a regular SPI transfer on
  a controller that does not support it

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@exceet.de>
Tested-by: Frieder Schrempf <frieder.schrempf@exceet.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9ab65fb2738e6cc0d7d5378f076010239f939ab0..c85b0cf7b4a9478e047f8f0bdc5420b8acd8ef2a 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/mod_devicetable.h>
 #include <linux/spi/spi.h>
+#include <linux/spi/spi-mem.h>
 #include <linux/of_gpio.h>
 #include <linux/pm_runtime.h>
 #include <linux/pm_domain.h>
@@ -2071,12 +2072,19 @@ static int of_spi_register_master(struct spi_controller *ctlr)
 static int spi_controller_check_ops(struct spi_controller *ctlr)
 {
        /*
-        * The controller must at least implement one of the ->transfer()
-        * hooks.
+        * 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 (!ctlr->transfer && !ctlr->transfer_one &&
-           !ctlr->transfer_one_message)
+       if (ctlr->mem_ops) {
+               if (!ctlr->mem_ops->exec_op)
+                       return -EINVAL;
+       } else if (!ctlr->transfer && !ctlr->transfer_one &&
+                  !ctlr->transfer_one_message) {
                return -EINVAL;
+       }
 
        return 0;
 }
@@ -2187,10 +2195,14 @@ int spi_register_controller(struct spi_controller *ctlr)
                        spi_controller_is_slave(ctlr) ? "slave" : "master",
                        dev_name(&ctlr->dev));
 
-       /* If we're using a queued driver, start the queue */
-       if (ctlr->transfer)
+       /*
+        * If we're using a queued driver, start the queue. Note that we don't
+        * need the queueing logic if the driver is only supporting high-level
+        * memory operations.
+        */
+       if (ctlr->transfer) {
                dev_info(dev, "controller is unqueued, this is deprecated\n");
-       else {
+       } else if (ctlr->transfer_one || ctlr->transfer_one_message) {
                status = spi_controller_initialize_queue(ctlr);
                if (status) {
                        device_del(&ctlr->dev);
@@ -2920,6 +2932,13 @@ static int __spi_async(struct spi_device *spi, struct spi_message *message)
 {
        struct spi_controller *ctlr = spi->controller;
 
+       /*
+        * Some controllers do not support doing regular SPI transfers. Return
+        * ENOTSUPP when this is the case.
+        */
+       if (!ctlr->transfer)
+               return -ENOTSUPP;
+
        message->spi = spi;
 
        SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics, spi_async);