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

[Boris Brezillon <boris.brezillon@collabora.com>]

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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