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

[Pavel Machek <pavel@denx.de>]

On Thu 2014-10-02 04:47:23, Marek Vasut wrote:
> 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.

Well, if you have >16M flash and if you need bootrom to work with it.

AFAICT, as long as you avoid using SPI from bootrom (socrates will happily run
from SD card, for example), reliable operation should be possible. And you can still use
SPI from Linux and u-boot...
									Pavel