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

[Marek Vasut <marex@denx.de>]

On Thursday, October 02, 2014 at 10:40:52 AM, Pavel Machek wrote:
> 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...

SD has the same problem if you don't have proper reset logic for it ;-)

Best regards,
Marek Vasut