[U-Boot] [PATCH 00/16] SF: Migrate to Linux SPI NOR framework

[Jagan Teki]

On Sat, Dec 15, 2018 at 7:29 PM Jagan Teki <jagan at amarulasolutions.com> wrote:
>
> On Fri, Dec 14, 2018 at 10:12 PM Vignesh R <vigneshr at ti.com> wrote:
> >
> > >>
> > >>     > 2) For BAR support, lets place it as it is and support via
> > > spi-nor
> > >>
> > >     >     Problem is, it not desirable to use BAR as default because its not
> > >     >     stateless and does not work with all flash parts. OTOH, it
> > >     seems like 4
> > >     >     byte addressing (stateless dedicated opcode or with enter/exit
> > >     4 byte
> > >     >     mode) seems to be standard.
> > >     >     Also, Linux doesn't support BAR and haven't seen any request
> > >     for BAR
> > >     >     support. Why support additional feature and burden of
> > >     maintaining when
> > >     >     it may not be needed.
> > >     >
> > >     >     But if you insist, I just have to add BAR support back.
> > >     >
> > >     >
> > >     > But if we do that, could we please have a config option so that I can
> > >     > somehow ensure only 4 byte opcoses are used that don't change some
> > >     state
> > >     > in the chip?
> > >     >
> > >
> > >     I am afraid BAR support would be the default as Jagan suggests not to
> > >     change existing behavior. You would have to disable SPI_FLASH_BAR to use
> > >     4 Byte addressing opcodes.
> > >
> > >
> > > Honestly, I don't like the idea of making BAR the default. Why can't we
> > > go the Linux way and enable BAR (maybe then as default) for boards that
> > > need it only?
> > >
> >
> > Jagan, would that be acceptable?
>
> Better way to have some controller flag to check we go with 3-byte or
> 4-byte addressing if flash > 16MiB. anyway let me give some time, will
> come back for the better to way to go this. ofcourse CONFIG would
> require if BAR handling code occupy more foot-print, but we have to
> enable based some controller indication.

another approach can be do some sanity transfer if the flash > 16MiB
with 4-byte addressing failure can lead to enable BAR.