[RFC] spi-nor: fix cross die reads on Micron multi-die devices

[Boris Brezillon]

Adam, Bean,

On Wed, 20 Jan 2016 12:01:06 +0000
Adam Somerville <adamsomerville at gmail.com> wrote:

> Hi,
> 
> Thanks for looking at the this.
> 
> I can rewrite so it only affects N25Q devices, I hoped a simpler
> implementation would outweigh the small overhead incurred on non
> affected devices.

I tend to think the same way: not sure the performance penalty is worth
the pain.

Best Regards,

Boris

> 
> Do you know if there are any plans for MT25* based multi-die devices
> and if they would have the same issue?
> 
> Thanks,
> 
> Adam
> 
> On Wed, Jan 20, 2016 at 2:45 AM, Bean Huo 霍斌斌 (beanhuo)
> <beanhuo at micron.com> wrote:
> > Hi, Adam
> > This is true, but this only exist in Micron 65nm spi nor N25Q.
> > For our 45nm spi nor MT25Q , MT25TL and MT25Q, does exist this question.
> > So I think, can you differentiate between these in your patch?
> >
> >> From: Adam Somerville <adamsomerville at gmail.com>
> >>
> >> So as far as I can see there is a bug in the spi-nor driver when issuing die
> >> boundary crossing reads on Micron multi-die devices.
> >> Micron N25Q512A, N25Q00AA and probably any other Micron multi-die
> >> devices do not support a single read request that crosses a die boundary.
> >>
> >> The current behaviour is that the address on the device wraps back to the
> >> start of the first die, with any data returned beyond the boundary being from
> >> the start of the first die.
> >>



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com