[PATCH V4 2/2] mtd: rawnand: qcom: set BAM mode only if not set already

[Sivaprakash Murugesan <sivaprak@codeaurora.org>]

BAM is DMA controller on QCOM ipq platforms, BAM mode on NAND driver
is set by writing BAM_MODE_EN bit on NAND_CTRL register.

NAND_CTRL is an operational register and in BAM mode operational
registers are read only.

So, before enabling BAM mode by writing the NAND_CTRL register, check
if BAM mode was already enabled by the bootloader, and enable BAM mode
only if it is not enabled already.

Signed-off-by: Sivaprakash Murugesan <sivaprak@codeaurora.org>
---
 drivers/mtd/nand/raw/qcom_nandc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
index 78b5f21..a3ef428 100644
--- a/drivers/mtd/nand/raw/qcom_nandc.c
+++ b/drivers/mtd/nand/raw/qcom_nandc.c
@@ -2784,7 +2784,14 @@ static int qcom_nandc_setup(struct qcom_nand_controller *nandc)
 	/* enable ADM or BAM DMA */
 	if (nandc->props->is_bam) {
 		nand_ctrl = nandc_read(nandc, NAND_CTRL);
-		nandc_write(nandc, NAND_CTRL, nand_ctrl | BAM_MODE_EN);
+		/* NAND_CTRL is an operational registers, and CPU
+		 * access to operational registers are read only
+		 * in BAM mode. So update the NAND_CTRL register
+		 * only if it is not in BAM mode. In most cases BAM
+		 * mode will be enabled in bootloader
+		 */
+		if (!(nand_ctrl | BAM_MODE_EN))
+			nandc_write(nandc, NAND_CTRL, nand_ctrl | BAM_MODE_EN);
 	} else {
 		nandc_write(nandc, NAND_FLASH_CHIP_SELECT, DM_EN);
 	}
-- 
2.7.4


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