From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Martin DEVERA <devik@eaxlabs.cz>, linux-mtd@lists.infradead.org
Subject: Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy
Date: Thu, 9 Jan 2020 19:02:40 +0100 [thread overview]
Message-ID: <20200109190240.6fee87fb@xps13> (raw)
In-Reply-To: <0501ddbd-9e0f-62ec-ab57-d092502680d5@eaxlabs.cz>
Hi Martin,
Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 18:43:46
+0100:
> On 1/9/20 6:22 PM, Miquel Raynal wrote:
> > 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?
> >
> Can you give me some guidance please ? Where should I add more comment to
> the git commit or to the C code ? I tried to comment both commit and code, probably
> you find the comments not clear enough ?
Sorry for not explaining: Could you add the example to the commit
message? The comment is fine, besides the fact that it should start
like this:
/*
* Bla bla bla
Also please change the commit title, maybe
mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough
Thanks,
Miquèl
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2020-01-09 18:03 UTC|newest]
Thread overview: 8+ 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
[not found] ` <0501ddbd-9e0f-62ec-ab57-d092502680d5@eaxlabs.cz>
2020-01-09 18:02 ` Miquel Raynal [this message]
2020-01-09 18:04 ` Miquel Raynal
2020-01-16 13:54 ` [PATCH] mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough Martin Devera
2020-03-10 18:34 ` Miquel Raynal
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200109190240.6fee87fb@xps13 \
--to=miquel.raynal@bootlin.com \
--cc=devik@eaxlabs.cz \
--cc=linux-mtd@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).