linux-kernel - Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

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Date:   Thu, 9 Jan 2020 16:37:52 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Martin Devera <devik@...labs.cz>
Cc:     linux-kernel@...r.kernel.org, jan.pohanka@...z.cz,
        Christophe Kerello <christophe.kerello@...com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

Hi Martin,

Martin Devera <devik@...labs.cz> wrote on Tue, 10 Dec 2019 16:03:18
+0100:

> The used way to compute jiffies timeout brokes when
> jiffie difference is 1. Simply add 1 - it has no other
> side effects.
> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> exactly in this way.
> 
> Signed-off-by: Martin Devera <devik@...labs.cz>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index d527e448ce19..beab3a775cc7 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
>  	if (ret)
>  		return ret;
>  
> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
> +	/* +1 below is necessary because if we are now in the last fraction
> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
> +	 * small jiffy fraction - possibly leading to false timeout
> +	 */
> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
>  	do {
>  		ret = nand_read_data_op(chip, &status, sizeof(status), true);
>  		if (ret)

I don't really what you are fixing here, I suspect the root cause to be
a wrongly calculated timeout_ms in the calling driver.

It is the responsibility of the caller to use this function with a
relevant timeout_ms parameter. Maybe Christophe can help you here?


Thanks,
Miquèl