[PATCH v2 5/9] spi: spi-mem: Allow masters to transfer dummy cycles directly by hardware

[Sowjanya Komatineni]

This patch adds a flag SPI_MASTER_USES_HW_DUMMY_CYCLES for the controllers
that support transfer of dummy cycles by the hardware directly.

For controller with this flag set, spi-mem driver will skip dummy bytes
transfer in the spi message.

Controller drivers can get the number of dummy cycles from spi_message.

Signed-off-by: Sowjanya Komatineni <skomatin...@nvidia.com>
---
 drivers/spi/spi-mem.c   | 18 +++++++++++-------
 include/linux/spi/spi.h |  8 ++++++++
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index f3a3f19..38a523b 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -350,13 +350,17 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct 
spi_mem_op *op)
        }
 
        if (op->dummy.nbytes) {
-               memset(tmpbuf + op->addr.nbytes + 1, 0xff, op->dummy.nbytes);
-               xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
-               xfers[xferpos].len = op->dummy.nbytes;
-               xfers[xferpos].tx_nbits = op->dummy.buswidth;
-               spi_message_add_tail(&xfers[xferpos], &msg);
-               xferpos++;
-               totalxferlen += op->dummy.nbytes;
+               if (ctlr->flags & SPI_MASTER_USES_HW_DUMMY_CYCLES) {
+                       msg.dummy_cycles = (op->dummy.nbytes * 8) / 
op->dummy.buswidth;
+               } else {
+                       memset(tmpbuf + op->addr.nbytes + 1, 0xff, 
op->dummy.nbytes);
+                       xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
+                       xfers[xferpos].len = op->dummy.nbytes;
+                       xfers[xferpos].tx_nbits = op->dummy.buswidth;
+                       spi_message_add_tail(&xfers[xferpos], &msg);
+                       xferpos++;
+                       totalxferlen += op->dummy.nbytes;
+               }
        }
 
        if (op->data.nbytes) {
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index aa09fdc..2024149 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -512,6 +512,8 @@ struct spi_controller {
 
 #define SPI_MASTER_GPIO_SS             BIT(5)  /* GPIO CS must select slave */
 
+#define SPI_MASTER_USES_HW_DUMMY_CYCLES        BIT(6)  /* HW dummy bytes 
transfer */
+
        /* flag indicating this is an SPI slave controller */
        bool                    slave;
 
@@ -1022,6 +1024,12 @@ struct spi_message {
        unsigned                actual_length;
        int                     status;
 
+       /*
+        * dummy cycles in the message transfer. This is used by the controller
+        * drivers supports transfer of dummy cycles directly by the hardware.
+        */
+       u8                      dummy_cycles;
+
        /* for optional use by whatever driver currently owns the
         * spi_message ...  between calls to spi_async and then later
         * complete(), that's the spi_controller controller driver.
-- 
2.7.4