Re: [PATCH] Add support for flag status register on Micron chips

[Marek Vasut]

On Wednesday, April 09, 2014 at 08:14:49 PM, Graham Moore wrote:
> On Wed, Apr 9, 2014 at 6:09 AM, Gerhard Sittig <gsi@xxxxxxx> wrote:
> > On Wed, 2014-04-09 at 12:03 +0200, Marek Vasut wrote:
> >> On Tuesday, April 08, 2014 at 06:12:49 PM, grmoore@xxxxxxxxxx wrote:
> >> > From: Graham Moore <grmoore@xxxxxxxxxx>
> >> > 
> >> > This is a slightly different version of the patch that Insop Song
> >> > submitted
> >> > (http://marc.info/?i=201403012022.10111.marex%20()%20denx%20!%20de).
> >> > 
> >> > I talked to Insop, and he agreed I should submit this patch as a
> >> > follow-on to his.
> >> > 
> >> > This patch uses a flag in the m25p_ids[] array to determine which
> >> > chips need to use the FSR (Flag Status Register).
> >> > 
> >> > Rationale for using the FSR:
> >> > 
> >> > The Micron data sheets say we have to do this, at least for the
> >> > multi-die 512M and 1G parts (n25q512 and n25q00).  In practice, if we
> >> > don't check the FSR for program/erase status, and we rely solely on
> >> > the status register (SR), then we get corrupted data in the flash.
> 
> [...]
> 
> >> > Micron told us (Altera) that for multi-die chips based on the 65nm
> >> > 256MB die, we need to check the SR first, then check the FSR, which
> >> > is why the wait_for_fsr_ready function does that.  Future chips based
> >> > on 45 nm 512MB die will use the FSR only.
> > 
> > This sounds to me similar to polling the NAND's R/B pin until the
> > operation has completed, to then fetch the STATUS byte to
> > determine the execution's result.  Does this sound plausible?
> > For NOR, do you poll for the "busy" condition to deassert, and
> > check for success then?
> 
> Sounds plausible to me.  We poll the SR until not busy, then poll the
> FSR until it's not busy.  Success is when FSR busy is deasserted
> within the timeout.
> 
> Micron said we have to read the FSR "at least once", so we don't
> read it once for every die or anything like that.  I ran a quick
> test, and for both the 2-die and 4-die parts, the FSR shows not busy
> on the first read after SR not busy.

I'd love to know how this FSR-not-busy is exactly related to SR-not-busy, but I 
guess only Micron can tell :-/

Best regards,
Marek Vasut
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