[PATCH] Check flag status register for Micron n25q512a

[Jagan Teki]

Hi All,

On Wed, Mar 5, 2014 at 3:15 AM, Chuck Peplinski <chuck at 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.


thanks!
-- 
Jagan.