mtd: rawnand: denali: fix a race condition when DMA is kicked

Based on Linux commit cf51e4b9c34407bf0c3d9b582b7837e047e1df47

Add the register read-back, commenting why this is necessary.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
index bbfa3b6..e0eb133 100644 (file)
--- a/drivers/mtd/nand/raw/denali.c
+++ b/drivers/mtd/nand/raw/denali.c
@@ -587,6 +587,12 @@ static int denali_dma_xfer(struct denali_nand_info *denali, void *buf,
        }
 
        iowrite32(DMA_ENABLE__FLAG, denali->reg + DMA_ENABLE);
+       /*
+        * The ->setup_dma() hook kicks DMA by using the data/command
+        * interface, which belongs to a different AXI port from the
+        * register interface.  Read back the register to avoid a race.
+        */
+       ioread32(denali->reg + DMA_ENABLE);
 
        denali_reset_irq(denali);
        denali->setup_dma(denali, dma_addr, page, write);