From cf51e4b9c34407bf0c3d9b582b7837e047e1df47 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Thu, 13 Sep 2018 14:58:49 +0900 Subject: [PATCH] mtd: rawnand: denali: fix a race condition when DMA is kicked I thought the read-back of the DMA_ENABLE register was unnecessary (at least it is working on my boards), then deleted it in commit 586a2c52909d ("mtd: nand: denali: squash denali_enable_dma() helper into caller"). Sorry, I was wrong - it caused a timing issue on Cyclone5 SoCFPGAs. Revive the register read-back, commenting why this is necessary. Fixes: 586a2c52909d ("mtd: nand: denali: squash denali_enable_dma() helper into caller") Cc: Reported-by: Steffen Trumtrar Signed-off-by: Masahiro Yamada Reviewed-by: Miquel Raynal Signed-off-by: Boris Brezillon --- drivers/mtd/nand/raw/denali.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c index 67b2065e7a19..b864b93dd289 100644 --- a/drivers/mtd/nand/raw/denali.c +++ b/drivers/mtd/nand/raw/denali.c @@ -596,6 +596,12 @@ 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);