Re: [PATCH] mtd: rawnand: fsmc: Make sure we wait tWB before polling the STATUS reg

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Boris,

On Thu,  3 May 2018 09:45:44 +0200, Boris Brezillon
<boris.brezillon@bootlin.com> wrote:

> NAND chips require a bit of time to take the NAND operation into account
> and set the BUSY bit in the STATUS reg. Make sure we don't poll the
> STATUS reg too early.
> 
> Fixes: 4da712e70294 ("mtd: nand: fsmc: use ->exec_op()")
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> ---
>  drivers/mtd/nand/raw/fsmc_nand.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/fsmc_nand.c b/drivers/mtd/nand/raw/fsmc_nand.c
> index 28c48dcc514e..0960665858b7 100644
> --- a/drivers/mtd/nand/raw/fsmc_nand.c
> +++ b/drivers/mtd/nand/raw/fsmc_nand.c
> @@ -18,6 +18,7 @@
>  
>  #include <linux/clk.h>
>  #include <linux/completion.h>
> +#include <linux/delay.h>
>  #include <linux/dmaengine.h>
>  #include <linux/dma-direction.h>
>  #include <linux/dma-mapping.h>
> @@ -695,6 +696,13 @@ static int fsmc_exec_op(struct nand_chip *chip, const struct nand_operation *op,
>  			pr_debug("  ->WAITRDY  [max %d ms]\n",
>  				 instr->ctx.waitrdy.timeout_ms);
>  
> +			/*
> +			 * Make sure we wait tWB before polling the STATUS
> +			 * register.
> +			 */
> +			if (op_id && op->instrs[op_id - 1].delay_ns)
> +				ndelay(op->instrs[op_id - 1].delay_ns);
> +
>  			ret = nand_soft_waitrdy(chip,
>  						instr->ctx.waitrdy.timeout_ms);
>  			break;

I'm afraid that we encounter this exact same issue with all the drivers
using nand_soft_waitrdy() whenever the controller does not already
wait for tWB. Could we force a tWB_max delay directly inside
nand_soft_waitrdy()?

Thanks,
Miquèl

-- 
Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com