linux-kernel - [PATCH v5 1/5] spi: cadence: Ensure data lines set to low during dummy-cycle period

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Date: Mon, 27 May 2024 01:42:12 -0700
From: Witold Sadowski <wsadowski@...vell.com>
To: <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <devicetree@...r.kernel.org>
CC: <broonie@...nel.org>, <robh@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <pthombar@...ence.com>, Witold Sadowski <wsadowski@...vell.com>
Subject: [PATCH v5 1/5] spi: cadence: Ensure data lines set to low during dummy-cycle period

During dummy-cycles xSPI will switch GPIO into Hi-Z mode. In that dummy
period voltage on data lines will slowly drop, what can cause
unintentional modebyte transmission. Value send to SPI memory chip will
depend on last address, and clock frequency.
To prevent unforeseen consequences of that behaviour, force send
single modebyte(0x00).
Modebyte will be send only if number of dummy-cycles is not equal
to 0. Code must also reduce dummycycle byte count by one - as one byte
is send as modebyte.

Signed-off-by: Witold Sadowski <wsadowski@...vell.com>
---
 drivers/spi/spi-cadence-xspi.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi-cadence-xspi.c b/drivers/spi/spi-cadence-xspi.c
index 8648b8eb080d..cdce2e280f66 100644
--- a/drivers/spi/spi-cadence-xspi.c
+++ b/drivers/spi/spi-cadence-xspi.c
@@ -145,6 +145,9 @@
 #define CDNS_XSPI_STIG_DONE_FLAG		BIT(0)
 #define CDNS_XSPI_TRD_STATUS			0x0104
 
+#define MODE_NO_OF_BYTES			GENMASK(25, 24)
+#define MODEBYTES_COUNT			1
+
 /* Helper macros for filling command registers */
 #define CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_1(op, data_phase) ( \
 	FIELD_PREP(CDNS_XSPI_CMD_INSTR_TYPE, (data_phase) ? \
@@ -157,9 +160,10 @@
 	FIELD_PREP(CDNS_XSPI_CMD_P1_R2_ADDR3, ((op)->addr.val >> 24) & 0xFF) | \
 	FIELD_PREP(CDNS_XSPI_CMD_P1_R2_ADDR4, ((op)->addr.val >> 32) & 0xFF))
 
-#define CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_3(op) ( \
+#define CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_3(op, modebytes) ( \
 	FIELD_PREP(CDNS_XSPI_CMD_P1_R3_ADDR5, ((op)->addr.val >> 40) & 0xFF) | \
 	FIELD_PREP(CDNS_XSPI_CMD_P1_R3_CMD, (op)->cmd.opcode) | \
+	FIELD_PREP(MODE_NO_OF_BYTES, modebytes) | \
 	FIELD_PREP(CDNS_XSPI_CMD_P1_R3_NUM_ADDR_BYTES, (op)->addr.nbytes))
 
 #define CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_4(op, chipsel) ( \
@@ -173,12 +177,12 @@
 #define CDNS_XSPI_CMD_FLD_DSEQ_CMD_2(op) \
 	FIELD_PREP(CDNS_XSPI_CMD_DSEQ_R2_DCNT_L, (op)->data.nbytes & 0xFFFF)
 
-#define CDNS_XSPI_CMD_FLD_DSEQ_CMD_3(op) ( \
+#define CDNS_XSPI_CMD_FLD_DSEQ_CMD_3(op, dummybytes) ( \
 	FIELD_PREP(CDNS_XSPI_CMD_DSEQ_R3_DCNT_H, \
 		((op)->data.nbytes >> 16) & 0xffff) | \
 	FIELD_PREP(CDNS_XSPI_CMD_DSEQ_R3_NUM_OF_DUMMY, \
 		  (op)->dummy.buswidth != 0 ? \
-		  (((op)->dummy.nbytes * 8) / (op)->dummy.buswidth) : \
+		  (((dummybytes) * 8) / (op)->dummy.buswidth) : \
 		  0))
 
 #define CDNS_XSPI_CMD_FLD_DSEQ_CMD_4(op, chipsel) ( \
@@ -351,6 +355,7 @@ static int cdns_xspi_send_stig_command(struct cdns_xspi_dev *cdns_xspi,
 	u32 cmd_regs[6];
 	u32 cmd_status;
 	int ret;
+	int dummybytes = op->dummy.nbytes;
 
 	ret = cdns_xspi_wait_for_controller_idle(cdns_xspi);
 	if (ret < 0)
@@ -365,7 +370,12 @@ static int cdns_xspi_send_stig_command(struct cdns_xspi_dev *cdns_xspi,
 	memset(cmd_regs, 0, sizeof(cmd_regs));
 	cmd_regs[1] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_1(op, data_phase);
 	cmd_regs[2] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_2(op);
-	cmd_regs[3] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_3(op);
+	if (dummybytes != 0) {
+		cmd_regs[3] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_3(op, 1);
+		dummybytes--;
+	} else {
+		cmd_regs[3] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_3(op, 0);
+	}
 	cmd_regs[4] = CDNS_XSPI_CMD_FLD_P1_INSTR_CMD_4(op,
 						       cdns_xspi->cur_cs);
 
@@ -375,7 +385,7 @@ static int cdns_xspi_send_stig_command(struct cdns_xspi_dev *cdns_xspi,
 		cmd_regs[0] = CDNS_XSPI_STIG_DONE_FLAG;
 		cmd_regs[1] = CDNS_XSPI_CMD_FLD_DSEQ_CMD_1(op);
 		cmd_regs[2] = CDNS_XSPI_CMD_FLD_DSEQ_CMD_2(op);
-		cmd_regs[3] = CDNS_XSPI_CMD_FLD_DSEQ_CMD_3(op);
+		cmd_regs[3] = CDNS_XSPI_CMD_FLD_DSEQ_CMD_3(op, dummybytes);
 		cmd_regs[4] = CDNS_XSPI_CMD_FLD_DSEQ_CMD_4(op,
 							   cdns_xspi->cur_cs);
 
-- 
2.43.0