[Patch 1/1] spi: Fix pxa2xx_spi.c chip select sequence error

[Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>]

From: Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>

Applies to kernel 2.6.25-rc1

Fixes a sequencing bug in spi driver pxa2xx_spi.c in which the chip
select for a transfer may be asserted before the transmission mode is
set on the interface.  As a result of this bug, the pins of the
interface can make extra transitions after chip select is set and
before the intended clock/data signals begin.  This only occurs on the
first transfer following a change in transmission mode.  The fix
assures that all modes are set on the interface before asserting chip
select.

This bug was introduced in a patch merged on 2006/12/10, kernel 2.6.20.

The patch defines an additional bit in:
include/asm-arm/arch-pxa/regs-ssp.h
for 2.6.25 and newer kernels

but this addition must be made in:
include/asm-arm/arch-pxa/pxa-regs.h
for kernels between 2.6.20 and 2.6.24, inclusive

Signed-off-by: Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>

---

 drivers/spi/pxa2xx_spi.c            |   48 ++++++++++++++++++--------
 include/asm-arm/arch-pxa/regs-ssp.h |    1 
 2 files changed, 36 insertions(+), 13 deletions(-)

diff -Nurp linux-2.6.25-rc1/drivers/spi/pxa2xx_spi.c linux-2.6.25-rc1_cs_patch/drivers/spi/pxa2xx_spi.c
--- linux-2.6.25-rc1/drivers/spi/pxa2xx_spi.c	2008-02-12 21:52:35.000000000 +0000
+++ linux-2.6.25-rc1_cs_patch/drivers/spi/pxa2xx_spi.c	2008-02-17 21:30:23.000000000 +0000
@@ -51,13 +51,19 @@ MODULE_LICENSE("GPL");
 #define RESET_DMA_CHANNEL (DCSR_NODESC | DMA_INT_MASK)
 #define IS_DMA_ALIGNED(x) (((u32)(x)&0x07)==0)
 
-/* for testing SSCR1 changes that require SSP restart, basically
- * everything except the service and interrupt enables */
-#define SSCR1_CHANGE_MASK (SSCR1_TTELP | SSCR1_TTE | SSCR1_EBCEI | SSCR1_SCFR \
+/*
+ * for testing SSCR1 changes that require SSP restart, basically
+ * everything except the service and interrupt enables, the pxa270 developer
+ * manual says only SSCR1_SCFR, SSCR1_SPH, SSCR1_SPO need to be in this
+ * list, but the PXA255 dev man says all bits without really meaning the
+ * service and interrupt enables
+ */
+#define SSCR1_CHANGE_MASK (SSCR1_TTELP | SSCR1_TTE | SSCR1_SCFR \
 				| SSCR1_ECRA | SSCR1_ECRB | SSCR1_SCLKDIR \
-				| SSCR1_RWOT | SSCR1_TRAIL | SSCR1_PINTE \
-				| SSCR1_STRF | SSCR1_EFWR |SSCR1_RFT \
-				| SSCR1_TFT | SSCR1_SPH | SSCR1_SPO | SSCR1_LBM)
+				| SSCR1_SFRMDIR | SSCR1_RWOT | SSCR1_TRAIL \
+				| SSCR1_IFS | SSCR1_STRF | SSCR1_EFWR \
+				| SSCR1_RFT | SSCR1_TFT | SSCR1_MWDS \
+				| SSCR1_SPH | SSCR1_SPO | SSCR1_LBM)
 
 #define DEFINE_SSP_REG(reg, off) \
 static inline u32 read_##reg(void *p) { return __raw_readl(p + (off)); } \
@@ -973,9 +979,6 @@ static void pump_transfers(unsigned long
 		if (drv_data->ssp_type == PXA25x_SSP)
 			DCMD(drv_data->tx_channel) |= DCMD_ENDIRQEN;
 
-		/* Fix me, need to handle cs polarity */
-		drv_data->cs_control(PXA2XX_CS_ASSERT);
-
 		/* Clear status and start DMA engine */
 		cr1 = chip->cr1 | dma_thresh | drv_data->dma_cr1;
 		write_SSSR(drv_data->clear_sr, reg);
@@ -985,9 +988,6 @@ static void pump_transfers(unsigned long
 		/* Ensure we have the correct interrupt handler	*/
 		drv_data->transfer_handler = interrupt_transfer;
 
-		/* Fix me, need to handle cs polarity */
-		drv_data->cs_control(PXA2XX_CS_ASSERT);
-
 		/* Clear status  */
 		cr1 = chip->cr1 | chip->threshold | drv_data->int_cr1;
 		write_SSSR(drv_data->clear_sr, reg);
@@ -998,14 +998,36 @@ static void pump_transfers(unsigned long
 		|| (read_SSCR1(reg) & SSCR1_CHANGE_MASK) !=
 			(cr1 & SSCR1_CHANGE_MASK)) {
 
+		/* stop the SSP, and update the other bits */
 		write_SSCR0(cr0 & ~SSCR0_SSE, reg);
 		if (drv_data->ssp_type != PXA25x_SSP)
 			write_SSTO(chip->timeout, reg);
-		write_SSCR1(cr1, reg);
+		/* first set CR1 without interrupt and service enables */
+		write_SSCR1(cr1 & SSCR1_CHANGE_MASK, reg);
+		/* restart the SSP */
 		write_SSCR0(cr0, reg);
+
+		/* FIXME, need to handle cs polarity,
+		 * this driver uses struct pxa2xx_spi_chip.cs_control to
+		 * specify a CS handling function, and it ignores most
+		 * struct spi_device.mode[s], including SPI_CS_HIGH */
+		drv_data->cs_control(PXA2XX_CS_ASSERT);
+
+		/* after chip select, release the data by enabling service
+		 * requests and interrupts, without changing any mode bits */
+		write_SSCR1(cr1, reg);
 	} else {
 		if (drv_data->ssp_type != PXA25x_SSP)
 			write_SSTO(chip->timeout, reg);
+
+		/* FIXME, need to handle cs polarity,
+		 * this driver uses struct pxa2xx_spi_chip.cs_control to
+		 * specify a CS handling function, and it ignores most
+		 * struct spi_device.mode[s], including SPI_CS_HIGH */
+		drv_data->cs_control(PXA2XX_CS_ASSERT);
+
+		/* after chip select, release the data by enabling service
+		 * requests and interrupts, without changing any mode bits */
 		write_SSCR1(cr1, reg);
 	}
 }
diff -Nurp linux-2.6.25-rc1/include/asm-arm/arch-pxa/regs-ssp.h linux-2.6.25-rc1_cs_patch/include/asm-arm/arch-pxa/regs-ssp.h
--- linux-2.6.25-rc1/include/asm-arm/arch-pxa/regs-ssp.h	2008-02-15 19:41:37.000000000 +0000
+++ linux-2.6.25-rc1_cs_patch/include/asm-arm/arch-pxa/regs-ssp.h	2008-02-15 19:47:40.000000000 +0000
@@ -85,6 +85,7 @@
 #define SSCR1_RSRE		(1 << 20)	/* Receive Service Request Enable */
 #define SSCR1_TINTE		(1 << 19)	/* Receiver Time-out Interrupt enable */
 #define SSCR1_PINTE		(1 << 18)	/* Peripheral Trailing Byte Interupt Enable */
+#define SSCR1_IFS		(1 << 16)	/* Invert Frame Signal */
 #define SSCR1_STRF		(1 << 15)	/* Select FIFO or EFWR */
 #define SSCR1_EFWR		(1 << 14)	/* Enable FIFO Write/Read */
 
-- 
Ned Forrester                                       nforrester-/d+BM93fTQY@public.gmane.org
Oceanographic Systems Lab                                  508-289-2226
Applied Ocean Physics and Engineering Dept.
Woods Hole Oceanographic Institution          Woods Hole, MA 02543, USA
http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212
http://www.whoi.edu/hpb/Site.do?id=1532
http://www.whoi.edu/page.do?pid=10079


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