[PATCH v1] spi: spi-mtk-nor: Add recovery mechanism for dma read timeout

[Bayi Cheng <bayi.cheng@xxxxxxxxxxxx>]

From: bayi cheng <bayi.cheng@xxxxxxxxxxxx>

The state machine of MTK spi nor controller may be disturbed by some
glitch signals from the relevant BUS during dma read, Although the
possibility of causing the dma read to fail is next to nothing,
However, if error-handling is not implemented, which makes the feature
somewhat risky.

Add an error-handling mechanism here, reset the state machine and
re-read the data when an error occurs.

Signed-off-by: bayi cheng <bayi.cheng@xxxxxxxxxxxx>
---
Change in v1:
  -Reset the state machine when dma read fails and read again.
---
---
 drivers/spi/spi-mtk-nor.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-mtk-nor.c b/drivers/spi/spi-mtk-nor.c
index d167699a1a96..c77d79da9a4c 100644
--- a/drivers/spi/spi-mtk-nor.c
+++ b/drivers/spi/spi-mtk-nor.c
@@ -80,6 +80,9 @@
 #define MTK_NOR_REG_DMA_FADR		0x71c
 #define MTK_NOR_REG_DMA_DADR		0x720
 #define MTK_NOR_REG_DMA_END_DADR	0x724
+#define MTK_NOR_REG_CG_DIS		0x728
+#define MTK_NOR_SFC_SW_RST		BIT(2)
+
 #define MTK_NOR_REG_DMA_DADR_HB		0x738
 #define MTK_NOR_REG_DMA_END_DADR_HB	0x73c
 
@@ -616,7 +619,18 @@ static int mtk_nor_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 			mtk_nor_set_addr(sp, op);
 			return mtk_nor_read_pio(sp, op);
 		} else {
-			return mtk_nor_read_dma(sp, op);
+			ret = mtk_nor_read_dma(sp, op);
+			if (ret) {
+				dev_err(sp->dev, "try to read again\n");
+				mtk_nor_rmw(sp, MTK_NOR_REG_CG_DIS, 0, MTK_NOR_SFC_SW_RST);
+				mb(); /* flush previous writes */
+				mtk_nor_rmw(sp, MTK_NOR_REG_CG_DIS, MTK_NOR_SFC_SW_RST, 0);
+				mb(); /* flush previous writes */
+				writel(MTK_NOR_ENABLE_SF_CMD, sp->base + MTK_NOR_REG_WP);
+				mtk_nor_setup_bus(sp, op);
+				ret = mtk_nor_read_dma(sp, op);
+			}
+			return ret;
 		}
 	}
 
-- 
2.18.0