Date:   Thu, 14 Feb 2019 01:34:16 +0000
From:   "liujian (CE)" <liujian56@...wei.com>
To:     Tokunori Ikegami <ikegami.t@...il.com>,
        "'Sobon, Przemyslaw'" <psobon@...zon.com>,
        'Boris Brezillon' <boris.brezillon@...labora.com>
CC:     "keescook@...omium.org" <keescook@...omium.org>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "richard@....at" <richard@....at>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "joakim.tjernlund@...inera.com" <joakim.tjernlund@...inera.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "ikegami_to@...oo.co.jp" <ikegami_to@...oo.co.jp>
Subject: RE: Re: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c
 do_write_buffer




Best Regards,
liujian


> -----Original Message-----
> From: Tokunori Ikegami [mailto:ikegami.t@...il.com]
> Sent: Friday, February 08, 2019 10:24 PM
> To: 'Sobon, Przemyslaw' <psobon@...zon.com>; 'Boris Brezillon'
> <boris.brezillon@...labora.com>
> Cc: keescook@...omium.org; marek.vasut@...il.com; richard@....at;
> linux-kernel@...r.kernel.org; joakim.tjernlund@...inera.com;
> linux-mtd@...ts.infradead.org; computersforpeace@...il.com;
> dwmw2@...radead.org; liujian (CE) <liujian56@...wei.com>;
> ikegami_to@...oo.co.jp
> Subject: RE: Re: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> 
> Hi Przemek-san,
> 
> Thank you so much for your explanation.
> 
> > I have seen a case myself where a value was written, chip changed
> > state to "ready" but when I was reading the value was incorrect.
> 
> I also know the similar issues for the both buffer and word write.
> Both issues were able to reproduce the write error behavior.
>   Note: The word write issue is able to reproduce now also.
> 
> Those were resolved by using chip_good() instead to check the state.
> 
> > This can happen as result of intermittent issue with flash. It is hard
> > to fall into scenario when testing on limited number of devices but
> > with large enough population you can see that.
> 
> If possible I would like to know the issue detail and its cause also.
> 
> > Another situation
> > is when a flash chip reaches its maximum number of writes. So for
> > example a chip is designed for 100k writes to a page. Once you reach
> > that number of writes you can have invalid data written to flash but
> > chip itself reports everything was good and switches to "ready" state.
> 
> Yes I see.
> 
> Regards,
> Ikegami
> 
> > -----Original Message-----
> > From: linux-mtd [mailto:linux-mtd-bounces@...ts.infradead.org] On
> > Behalf Of Sobon, Przemyslaw
> > Sent: Friday, February 8, 2019 8:51 AM
> > To: ikegami_to@...oo.co.jp; Boris Brezillon
> > Cc: keescook@...omium.org; marek.vasut@...il.com;
> > ikegami@...ied-telesis.co.jp; richard@....at;
> > linux-kernel@...r.kernel.org; joakim.tjernlund@...inera.com;
> > linux-mtd@...ts.infradead.org; computersforpeace@...il.com;
> > dwmw2@...radead.org; Liu Jian
> > Subject: RE: Re: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c
> > do_write_buffer
> >
> > Hi Ikegami,
> >
> > I have seen a case myself where a value was written, chip changed
> > state to "ready" but when I was reading the value was incorrect.
> > This can happen as result of intermittent issue with flash. It is hard
> > to fall into scenario when testing on limited number of devices but
> > with large enough population you can see that. Another situation is
> > when a flash chip reaches its maximum number of writes. So for example
> > a chip is designed for 100k writes to a page. Once you reach that
> > number of writes you can have invalid data written to flash but chip
> > itself reports everything was good and switches to "ready" state.
> >
> > Hope this explanation is clear. Please let me know.
> >
> > Regards,
> > Przemek
> >
> > > -----Original Message-----
> > > From: ikegami_to@...oo.co.jp <ikegami_to@...oo.co.jp>
> > > Sent: Thursday, February 7, 2019 3:00 PM
> > >
> > > Hi Przemek-san,
> > >
> > > Could you please explain the case detail that the value is written
> > incorrectly?
> > > I think that the value is only written correctly except a bug.
> > >
> > > Regards,
> > > Ikegami
> > >
> > > --- boris.brezillon@...labora.com wrote --- :
> > > > Hi Sobon,
> > > >
> > > > On Tue, 5 Feb 2019 22:28:44 +0000
> > > > "Sobon, Przemyslaw" <psobon@...zon.com> wrote:
> > > >
> > > > > > From: Boris Brezillon <bbrezillon@...nel.org>
> > > > > > Sent: Sunday, February 3, 2019 12:35 AM
> > > > > > > +Przemyslaw
> > > > > > >
> > > > > > > On Fri, 1 Feb 2019 07:30:39 +0800 Liu Jian
> > > > > > > <liujian56@...wei.com> wrote:
> > > > > > >
> > > > > > > > In function do_write_buffer(), in the for loop, there is a
> > > > > > > > case
> > > > > > > > chip_ready() returns 1 while chip_good() returns 0, so it
> > > > > > > > never break the loop.
> > > > > > > > To fix this, chip_good() is enough and it should timeout
> > > > > > > > if
> > it
> > > > > > > > stay bad for a while.
> > > > > > >
> > > > > > > Looks like Przemyslaw reported and fixed the same problem.
> > > > > > >
> > > > > > > >
> > > > > > > > Fixes: dfeae1073583(mtd: cfi_cmdset_0002: Change write
> > > > > > > > buffer to check correct value)
> > > > > > >
> > > > > > > Can you put the Fixes tag on a single, and the format is
> > > > > > >
> > > > > > > Fixes: <hash> ("message")
> > > > > > >
> > > > > > > > Signed-off-by: Yi Huaijie <yihuaijie@...wei.com>
> > > > > > > > Signed-off-by: Liu Jian <liujian56@...wei.com>
> > > > > > >
> > > > > > > [1]http://patchwork.ozlabs.org/patch/1025566/
> > > > > > >

So, do I need to send a v2 patch? Or use Przemyslaw's new patch http://patchwork.ozlabs.org/patch/1038395/

> > > > > > > > ---
> > > > > > > >  drivers/mtd/chips/cfi_cmdset_0002.c | 6 +++---
> > > > > > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > > > > > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > > > > > index 72428b6..818e94b 100644
> > > > > > > > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > > > > > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > > > > > @@ -1876,14 +1876,14 @@ static int __xipram
> > do_write_buffer(struct map_info *map, struct flchip *chip,
> > > > > > > >              continue;
> > > > > > > >          }
> > > > > > > >
> > > > > > > > -        if (time_after(jiffies, timeo) && !chip_ready(map,
> > adr))
> > > > > > > > -            break;
> > > > > > > > -
> > > > > > > >          if (chip_good(map, adr, datum)) {
> > > > > > > >              xip_enable(map, chip, adr);
> > > > > > > >              goto op_done;
> > > > > > > >          }
> > > > > > > >
> > > > > > > > +        if (time_after(jiffies, timeo))
> > > > > > > > +            break;
> > > > > > > > +
> > > > > > > >          /* Latency issues. Drop the lock, wait a while
> > > > > > > > and
> > retry */
> > > > > > > >          UDELAY(map, chip, adr, 1);
> > > > > > > >      }
> > > > > > >
> > > > > >
> > > > > > BTW, the patch itself looks good to me. Ikegami, can you
> > > > > > confirm
> > it does the right thing?
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Boris
> > > > > >
> > > > >
> > > > > One comment to this patch. If value is written incorrectly
> > > > > quickly we will be stuck in the loop even though nothing is going to
> change.
> > > > > For example a value was written incorrectly after 1us, the loop
> > > > > was set to 1ms, function will return after 1ms, this solution is
> > > > > not optimized for performance. I considered same when working on
> > > > > this
> > change and decided to do it different way.
> > > >
> > > > Seems like you're right if we assume that checking for GOOD state
> > > > does not require a delay after the READY check, but if that's not
> > > > the case and an extra delay is actually required, you might end up
> > > > with a BAD status while it could have turned GOOD at some point
> > > > with the 'check only for GOOD state until we timeout' approach.
> > > >
> > > > TBH, I don't know how CFI flashes work, so I'll let you guys sort
> > > > this out.
> > > >
> > > > Regards,
> > > >
> > > > Boris
> > > >
> > > > ______________________________________________________
> > > > Linux MTD discussion mailing list
> > > > http://lists.infradead.org/mailman/listinfo/linux-mtd/
> > > >
> > >
> > >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/

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