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

[Marek Vasut <marex@denx.de>]

On Tuesday, April 08, 2014 at 06:12:49 PM, grmoore@altera.com wrote:
> From: Graham Moore <grmoore@altera.com>
> 
> 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.

I talked to Gerhard yesterday and he told me there is something like that on 
ONFI NAND. I think I now understand why that new register is in-place. 
Apparently, in the ONFI NAND case, there is a READY and TRUE-READY signal and 
one of those reflects that _all_ the dies have finished their operation. This is 
in my opinion seriously misdesigned as it breaks any kind of backward 
compatibility.

> 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.

Can these SPI flash makers screw the design even more? OT: Why don't we have a 
single standard for all the SF chips which won't need all these crappy quirks 
:-(

Best regards,
Marek Vasut