spi: atmel-quadspi: Avoid overwriting delay register settings

Previously the MR and SCR registers were just set with the supposedly
required values, from cached register values (cached reg content
initialized to zero).

All parts fixed here did not consider the current register (cache)
content, which would make future support of cs_setup, cs_hold, and
cs_inactive impossible.

Setting SCBR in atmel_qspi_setup() erases a possible DLYBS setting from
atmel_qspi_set_cs_timing().  The DLYBS setting is applied by ORing over
the current setting, without resetting the bits first.  All writes to MR
did not consider possible settings of DLYCS and DLYBCT.
Signed-off-by: Alexander Dahl <ada@thorsis.com>
Fixes: f732646d ("spi: atmel-quadspi: Add support for configuring CS timing")
Link: https://patch.msgid.link/20240918082744.379610-2-ada@thorsis.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/atmel-quadspi.c

@@ -375,9 +375,9 @@ static int atmel_qspi_set_cfg(struct atmel_qspi *aq,
 	 * If the QSPI controller is set in regular SPI mode, set it in
 	 * Serial Memory Mode (SMM).
 	 */
-	if (aq->mr != QSPI_MR_SMM) {
-		atmel_qspi_write(QSPI_MR_SMM, aq, QSPI_MR);
-		aq->mr = QSPI_MR_SMM;
+	if (!(aq->mr & QSPI_MR_SMM)) {
+		aq->mr |= QSPI_MR_SMM;
+		atmel_qspi_write(aq->scr, aq, QSPI_MR);
 	}
 
 	/* Clear pending interrupts */
@@ -501,7 +501,8 @@ static int atmel_qspi_setup(struct spi_device *spi)
 	if (ret < 0)
 		return ret;
 
-	aq->scr = QSPI_SCR_SCBR(scbr);
+	aq->scr &= ~QSPI_SCR_SCBR_MASK;
+	aq->scr |= QSPI_SCR_SCBR(scbr);
 	atmel_qspi_write(aq->scr, aq, QSPI_SCR);
 
 	pm_runtime_mark_last_busy(ctrl->dev.parent);
@@ -534,6 +535,7 @@ static int atmel_qspi_set_cs_timing(struct spi_device *spi)
 	if (ret < 0)
 		return ret;
 
+	aq->scr &= ~QSPI_SCR_DLYBS_MASK;
 	aq->scr |= QSPI_SCR_DLYBS(cs_setup);
 	atmel_qspi_write(aq->scr, aq, QSPI_SCR);
 
@@ -549,8 +551,8 @@ static void atmel_qspi_init(struct atmel_qspi *aq)
 	atmel_qspi_write(QSPI_CR_SWRST, aq, QSPI_CR);
 
 	/* Set the QSPI controller by default in Serial Memory Mode */
-	atmel_qspi_write(QSPI_MR_SMM, aq, QSPI_MR);
-	aq->mr = QSPI_MR_SMM;
+	aq->mr |= QSPI_MR_SMM;
+	atmel_qspi_write(aq->mr, aq, QSPI_MR);
 
 	/* Enable the QSPI controller */
 	atmel_qspi_write(QSPI_CR_QSPIEN, aq, QSPI_CR);