Re: [PATCH] Check flag status register for Micron n25q512a

[Marek Vasut <marex@denx.de>]

On Thursday, March 06, 2014 at 11:03:50 AM, Harini Katakam wrote:
> Hi,
> 
> > -----Original Message-----
> > From: Jagan Teki [mailto:jagannadh.teki@gmail.com]
> > Sent: Thursday, March 06, 2014 2:56 PM
> > To: chuck@mds.com
> > Cc: Marek Vasut; linux-mtd@lists.infradead.org; Todd Legler (tlegler);
> > Harini Katakam
> > Subject: Re: [PATCH] Check flag status register for Micron n25q512a
> > 
> > Hi All,
> > 
> > On Wed, Mar 5, 2014 at 3:15 AM, Chuck Peplinski <chuck@mds.com> wrote:
> > > On 3/3/2014 6:29 PM, Marek Vasut wrote:
> > >>> FSR can apparently toggle without SR.
> > >> 
> > >> Is that documented anywhere ? How can that be ?
> > > 
> > > I'm looking at the data sheet for the part, n25q_512mb_1ce3v_65nm.pdf,
> > > from the Micron web site at
> > > http://www.micron.com/products/nor-flash/serial-nor-
> > 
> > flash#fullPart&236=10.
> > 
> > > The comment that led us in this direction is on page 62:
> > > 
> > > "ERASE Operations
> > > When the operation is in progress, the program or erase controller bit
> > > of the flag status register is set to 0. The flag status register must
> > > be polled for the operation status. When the operation completes, that
> > > bit is cleared to 1.
> > > Note that the flag status register must be polled even if operation
> > > times out."
> > > 
> > >> Hmmmm , I have a feeling that if you actually added wait_till_ready()
> > >> call at the end of _erase() and _write(), you would get the same
> > >> effect. This would in turn mean you are instead missing
> > >> wait_till_ready()
> > 
> > somewhere else.
> > 
> > >> Can you try using wait_till_ready() at the end of _erase() and
> > >> _write() please ?
> > > 
> > > That would be the standard code, right?  That's where we started and
> > > it did not work.
> > > 
> > > At some point I'll try some more tests.  I'm not blocked on this now,
> > > so it's not totally critical.
> > > One thing I notice:  The web site notes that this part stacks two 256M
> > > dies. Maybe that's why it is non-standard?
> > > Sure would be nice to hear from someone at Micron...
> > 
> > BTW: I have some information regarding this part.
> > 
> > We have tested this part both in u-boot and Linux where we could see an
> > issue while polling read_status, and then we moved to use flag_status
> > then we saw the consistent behavior.
> > 
> > Inputs we're got from Micron are:
> > 1. Micron (though not clearly documented), stated that flag_status is
> > clearly
> > 
> >     required to be polled, even though read_status reports the exact
> >     status. They are not willing to change the datasheet but plan on
> >     releasing an app note or something because this has led to a lot of
> >     confusion.
> > 
> > 2. At this moment, no one else has such weird design of needing an
> > flag_status poll.
> > 
> >     So checking for the device ID and polling flag_status looks like the
> >     only
> > 
> > option.
> > 
> > The same approach we tried as well.
> > 
> > CCing - Harini (tested flag_status on Linux) CCing - Todd Legler from
> > Micron.
> > 
> > Todd and Harini - Please share your inputs.
> 
> Micron devices with more than one die i.e. n25q_512mb and n25q_1gb
> have this additional check.
> Notes 14 and 15 under command definition table 18 describe this best.
> Although, it is stated that the WIP bit in status register is NOT of
> bit 7 in Flag status register, FSR still needs to be polled.
> 
> We had a discussion with Micron from which we learnt the following:
> 1. Program/erase operations in multi-die devices are not complete until
> Read FSR command receives a ready response form flash at least one time.
> 2. In addition, if you are doing a Write Non-volatile configuration
> register/ Write status register operation, the operation is only complete
> after FSR poll returns ready consecutively 2 or 4 times (as many times as
> the number of die). In this case, each time the chip select is toggled and
> Read FSR command is sent, response is sent by alternate die (1,2,1,2... or
> 1,2,3,4,1,2,3,4.....).
> 
> Todd, please add to this if you would like to elaborate.

Thanks for pointing this out.