[U-Boot] [RFC PATCH 4/4 v3] mtd: sf: Add CONFIG_SPI_N25Q256A_RESET for software-reset

[Marek Vasut <marex@denx.de>]

On Wednesday, October 01, 2014 at 09:04:48 PM, Jagan Teki wrote:
> On 2 October 2014 00:27, Stefan Roese <sr@denx.de> wrote:
> > On 01.10.2014 20:25, Marek Vasut wrote:
> >> On Wednesday, October 01, 2014 at 05:13:11 PM, Stefan Roese wrote:
> >>> This is needed for the SoCFPGA booting from SPI NOR flash
> >>> e.g. (N25Q256A). With these changes, the SoCrates can boot and
> >>> re-boot (reset) from SPI NOR flash without any problems.
> >> 
> >> Seems like your SPI NOR reset logic is buggy. Does any of [1] apply to
> >> your
> >> board please?
> >> 
> >> [1] http://www.rocketboards.org/foswiki/Documentation/SocBoardQspiBoot
> > 
> > Yes. This seems to be that case. But I can't change it right now. So this
> > "solution" with the soft-reset is better than nothing.
> 
> If this is some think that must require, any possibility to this
> resetting prior to u-boot?
> like preloader or in first stage boot loader or something.

You do understand, that this is a hardware bug on one particular board, right ? 
This can _not_ be reliably solved in software, not ever. I keep seeing people 
implementing one such workaround after the other in linux-mtd list, but sooner
or later, they discover that their workaround is not reliable. Without proper 
reset logic in place, a system simply cannot reliably reboot, since it has no
way to put all the hardware into defined state.

Also, the N25Qxxx chips are particularly crappy in this aspect, since they tend 
to happily get stuck in some weird undefined state during reboot. Proper reset
logic solves this issue, see the link above please.

Best regards,
Marek Vasut