spi: mpc52xx_psc_spi chipselect bugfix

According to the manual the "tdfOnExit" flag must be set on the last byte
we want to send.  The PSC controller holds SS low until the flag is set.

However, the flag was set always on the last byte of the FIFO,
independently if it is the last byte of the transfer.  This generates
spurious toggling of the SS signals that breaks the protocol of some
peripherals.  Fix.

Signed-off-by: Stefano Babic <[email protected]>
Acked-by: Grant Likely <[email protected]>
Signed-off-by: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/drivers/spi/mpc52xx_psc_spi.c b/drivers/spi/mpc52xx_psc_spi.c
index 0debe11b67b494a2f0ea4d49cb95598e43217c3d..3b97803e1d11b0f4114e1104bbfd93c76c932eab 100644 (file)
--- a/drivers/spi/mpc52xx_psc_spi.c
+++ b/drivers/spi/mpc52xx_psc_spi.c
@@ -142,6 +142,7 @@ static int mpc52xx_psc_spi_transfer_rxtx(struct spi_device *spi,
        unsigned rfalarm;
        unsigned send_at_once = MPC52xx_PSC_BUFSIZE;
        unsigned recv_at_once;
+       int last_block = 0;
 
        if (!t->tx_buf && !t->rx_buf && t->len)
                return -EINVAL;
@@ -151,15 +152,17 @@ static int mpc52xx_psc_spi_transfer_rxtx(struct spi_device *spi,
        while (rb < t->len) {
                if (t->len - rb > MPC52xx_PSC_BUFSIZE) {
                        rfalarm = MPC52xx_PSC_RFALARM;
+                       last_block = 0;
                } else {
                        send_at_once = t->len - sb;
                        rfalarm = MPC52xx_PSC_BUFSIZE - (t->len - rb);
+                       last_block = 1;
                }
 
                dev_dbg(&spi->dev, "send %d bytes...\n", send_at_once);
                for (; send_at_once; sb++, send_at_once--) {
                        /* set EOF flag before the last word is sent */
-                       if (send_at_once == 1)
+                       if (send_at_once == 1 && last_block)
                                out_8(&psc->ircr2, 0x01);
 
                        if (tx_buf)