linux-kernel - [43/74] spi/mpc512x-psc: optionally keep PSC SS asserted across xfer segmensts

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Message-ID: <lsq.1365374742.961917932@decadent.org.uk>
Date:	Sun, 07 Apr 2013 23:45:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Gerhard Sittig" <gerhard.sittig@....com>,
	"Mark Brown" <broonie@...nsource.wolfsonmicro.com>,
	"Anatolij Gustschin" <agust@...x.de>
Subject: [43/74] spi/mpc512x-psc: optionally keep PSC SS asserted across
 xfer segmensts

3.2.43-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Anatolij Gustschin <agust@...x.de>

commit 1ad849aee5f53353ed88d9cd3d68a51b03a7d44f upstream.

Some SPI slave devices require asserted chip select signal across
multiple transfer segments of an SPI message. Currently the driver
always de-asserts the internal SS signal for every single transfer
segment of the message and ignores the 'cs_change' flag of the
transfer description. Disable the internal chip select (SS) only
if this is needed and indicated by the 'cs_change' flag.

Without this change, each partial transfer of a surrounding
multi-part SPI transaction might erroneously change the SS
signal, which might prevent slaves from answering the request
that was sent in a previous transfer segment because the
transaction could be considered aborted (SS was de-asserted
before reading the response).

Reported-by: Gerhard Sittig <gerhard.sittig@....com>
Signed-off-by: Anatolij Gustschin <agust@...x.de>
Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/spi/spi-mpc512x-psc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/spi/spi-mpc512x-psc.c
+++ b/drivers/spi/spi-mpc512x-psc.c
@@ -164,7 +164,7 @@ static int mpc512x_psc_spi_transfer_rxtx

 		for (i = count; i > 0; i--) {
 			data = tx_buf ? *tx_buf++ : 0;
-			if (len == EOFBYTE)
+			if (len == EOFBYTE && t->cs_change)
 				setbits32(&fifo->txcmd, MPC512x_PSC_FIFO_EOF);
 			out_8(&fifo->txdata_8, data);
 			len--;

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