spi: spi-mtk-nor: Add recovery mechanism for dma read timeout

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@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221207055435.30557-1-bayi.cheng@mediatek.com
Signed-off-by: Mark Brown <broonie@kernel.org>

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
 
@@ -147,6 +150,15 @@ static inline int mtk_nor_cmd_exec(struct mtk_nor *sp, u32 cmd, ulong clk)
 	return ret;
 }
 
+static void mtk_nor_reset(struct mtk_nor *sp)
+{
+	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);
+}
+
 static void mtk_nor_set_addr(struct mtk_nor *sp, const struct spi_mem_op *op)
 {
 	u32 addr = op->addr.val;
@@ -609,7 +621,15 @@ 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 (unlikely(ret)) {
+				/* Handle rare bus glitch */
+				mtk_nor_reset(sp);
+				mtk_nor_setup_bus(sp, op);
+				return mtk_nor_read_dma(sp, op);
+			}
+
+			return ret;
 		}
 	}