Re: Re: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer

[<ikegami_to@yahoo.co.jp>]

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@collabora.com wrote --- :
> Hi Sobon,
> 
> On Tue, 5 Feb 2019 22:28:44 +0000
> "Sobon, Przemyslaw" <psobon@amazon.com> wrote:
> 
> > > From: Boris Brezillon <bbrezillon@kernel.org> 
> > > Sent: Sunday, February 3, 2019 12:35 AM  
> > > > +Przemyslaw
> > > > 
> > > > On Fri, 1 Feb 2019 07:30:39 +0800
> > > > Liu Jian <liujian56@huawei.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@huawei.com>
> > > > > Signed-off-by: Liu Jian <liujian56@huawei.com>  
> > > > 
> > > > [1]http://patchwork.ozlabs.org/patch/1025566/ 
> > > >   
> > > > > ---
> > > > >  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
> 
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> 


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