[U-Boot] [PATCH] sf: Add SPI_FLASH_4BYTE_MODE_ONLY option to support 4-byte mode

[Simon Goldschmidt]

Stefan Roese <sr at denx.de> schrieb am Mo., 6. Aug. 2018, 17:29:

>
>
> On 06.08.2018 17:27, Simon Goldschmidt wrote:
> >
> >
> > Stefan Roese <sr at denx.de <mailto:sr at denx.de>> schrieb am Mo., 6. Aug.
> > 2018, 17:23:
> >
> >     Hi Simon,
> >
> >     On 06.08.2018 17:15, Simon Goldschmidt wrote:
> >      >
> >      >
> >      > Stefan Roese <sr at denx.de <mailto:sr at denx.de> <mailto:sr at denx.de
> >     <mailto:sr at denx.de>>> schrieb am Mo., 6. Aug.
> >      > 2018, 16:34:
> >      >
> >      >     Some SPI NOR chips only support 4-byte mode addressing. Here
> >     the default
> >      >     3-byte mode does not work and leads to incorrect accesses.
> >     Setting this
> >      >     option enables the use of such SPI NOR chips, that only
> >     support this
> >      >     4-byte mode.
> >      >
> >      >
> >      > I think it would make more sense to enable 4-byte mode or 4-byte
> >     opcodes
> >      > on all chips with more than 16 mbyte rather than having to select
> at
> >      > compile time.
> >
> >     We need to be careful here. As setting the chip into 4-byte mode
> >     unconditionally (for bigger devices) will very likely cause boot
> >     problems with internal bootROMs expecting 3-byte mode.
> >
> >
> > I have a similar problem on socfpga where Linux 4.9 sets the chip into
> > 4-byte mode and SPL cannot use it on warm reboot. However, the bootROM
> > does not run on warm reboot on this platform.
>
> So in your "warm reboot" case, my option b) below would help, right?
>

Yes, I guess it would.

An even better idea would be to use stateless 4-byte opcodes. That's what
Linux does in more recent versions. But that would be a larger patch, I
guess. And with Jagan's bigger rework in his queue, I can't tell if this is
a good time to do so.


> b)
> Another idea would be to check the 3-byte / 4-byte mode of the SPI
> NOR device upon SPI NOR driver loading and use the selected mode
> accordingly. This could be done without compile time options but
> it would not help in general for users with bigger SPI NOR devices
> that support both modes.
>
> Thanks,
> Stefan
>