From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Martin DEVERA <devik@eaxlabs.cz>
Cc: linux-kernel@vger.kernel.org, jan.pohanka@merz.cz,
Christophe Kerello <christophe.kerello@st.com>,
Boris Brezillon <boris.brezillon@bootlin.com>,
Richard Weinberger <richard@nod.at>,
David Woodhouse <dwmw2@infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
Marek Vasut <marek.vasut@gmail.com>,
linux-mtd@lists.infradead.org
Subject: Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy
Date: Thu, 9 Jan 2020 18:22:42 +0100 [thread overview]
Message-ID: <20200109182242.03743cf7@xps13> (raw)
In-Reply-To: <73164aea-d889-21e4-4e7d-345ebd4e5197@eaxlabs.cz>
Hi Martin,
Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 17:17:30
+0100:
> On 1/9/20 4:37 PM, Miquel Raynal wrote:
> > Hi Martin,
> >
> > Martin Devera <devik@eaxlabs.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@eaxlabs.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?
> >
> Hi Miquel,
>
> assume that nand_soft_waitrdy is called with timeout_ms==1. I suppose it is
> valid case. Jiffies are 1000 for example (assume something more like 1000.99 -
> just before incrementing to 1001).
> We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001 (at least for my jiffies rate).
> nand_read_data_op is called for the first time and returns 0. During the call jiffies changes
> to 1001 thus "while loop" ends here (wrongly).
> Notice that routine was called with expected timeout 1ms but actual timeout used was something
> between 0...1ms (which I also measured by tracing & scope on the bus).
> Or is my analysis flawed somewhere ?
I agree with your analysis. Even if nand_soft_waitrdy will no longer be
used by the stm32 driver (Christophe sent a patch for that) I am fine
applying this change.
Could you add a comment to explain the '+1' and resend?
Thanks,
Miquèl
prev parent reply other threads:[~2020-01-09 17:22 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 15:03 [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy Martin Devera
2020-01-09 15:37 ` Miquel Raynal
2020-01-09 16:17 ` Martin DEVERA
2020-01-09 17:22 ` Miquel Raynal [this message]
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