[PATCH] spi/omap2_mcspi: disable and enable chan between each SPI transfer

[Jason Wang]

In current design, the SPI channel is always enable during the period
of handling a SPI message, it is risky when more than one SPI transfer
are included in a message. Current working route like that:
[
  SPI channel enable
  configure channel
  handle transfer #1
  configure channel
  handle transfer #2
  ...
  SPI channel disable
]
If we can disable channel before configure it and reenable
channel after it is configured, it will be more safe.

The commit a330ce2 "omap2_mcspi: Flush posted writes" make this risk
to a real problem for ads7846 driver on omap3530evm. The
ads7846 driver will send a SPI messge which includes,
[
  TX_ONLY transfer (1 byte)
  RX_ONLY transfer (2 bytes)
  TX_ONLY transfer (1 byte)
  RX_ONLY transfer (2 bytes)
]
If we don't add disable/reenable channel between TX and RX transfers,
the RX transfer will get wrong datas sent from slave.

Signed-off-by: Jason Wang <jason77.wang at gmail.com>
---
 drivers/spi/omap2_mcspi.c |   16 ++++++----------
 1 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c
index b3a94ca..1e3cb7b 100644
--- a/drivers/spi/omap2_mcspi.c
+++ b/drivers/spi/omap2_mcspi.c
@@ -408,7 +408,6 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
 				count -= (word_len <= 8)  ? 2 :
 					(word_len <= 16) ? 4 :
 					/* word_len <= 32 */ 8;
-				omap2_mcspi_set_enable(spi, 1);
 				return count;
 			}
 		}
@@ -430,8 +429,10 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
 				 (word_len <= 16) ? 2 :
 			       /* word_len <= 32 */ 4;
 		}
-		omap2_mcspi_set_enable(spi, 1);
 	}
+
+	omap2_mcspi_set_enable(spi, 0);
+
 	return count;
 }
 
@@ -517,8 +518,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						goto out;
 					}
 					c = 0;
-				} else if (c == 0 && tx == NULL) {
-					omap2_mcspi_set_enable(spi, 0);
 				}
 
 				*rx++ = __raw_readl(rx_reg);
@@ -570,8 +569,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						goto out;
 					}
 					c = 0;
-				} else if (c == 0 && tx == NULL) {
-					omap2_mcspi_set_enable(spi, 0);
 				}
 
 				*rx++ = __raw_readl(rx_reg);
@@ -623,8 +620,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						goto out;
 					}
 					c = 0;
-				} else if (c == 0 && tx == NULL) {
-					omap2_mcspi_set_enable(spi, 0);
 				}
 
 				*rx++ = __raw_readl(rx_reg);
@@ -646,7 +641,7 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 			dev_err(&spi->dev, "EOT timed out\n");
 	}
 out:
-	omap2_mcspi_set_enable(spi, 1);
+	omap2_mcspi_set_enable(spi, 0);
 	return count - c;
 }
 
@@ -894,7 +889,6 @@ static void omap2_mcspi_work(struct work_struct *work)
 		cs = spi->controller_state;
 		cd = spi->controller_data;
 
-		omap2_mcspi_set_enable(spi, 1);
 		list_for_each_entry(t, &m->transfers, transfer_list) {
 			if (t->tx_buf == NULL && t->rx_buf == NULL && t->len) {
 				status = -EINVAL;
@@ -931,6 +925,8 @@ static void omap2_mcspi_work(struct work_struct *work)
 
 			mcspi_write_chconf0(spi, chconf);
 
+			omap2_mcspi_set_enable(spi, 1);
+
 			if (t->len) {
 				unsigned	count;
 
-- 
1.5.6.5