[U-Boot] [RFC PATCH v2 00/11] SF: Migrate to Linux SPI NOR framework

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Vignesh,

Vignesh R <vigneshr@ti.com> wrote on Mon, 10 Dec 2018 23:08:38 +0530:

> On 10-Dec-18 6:32 PM, Jagan Teki wrote:
> > On Thu, Dec 6, 2018 at 11:55 PM Vignesh R <vigneshr@ti.com> wrote:  
> >>
> >> Hi Jagan,
> >>
> >> On 06-Dec-18 10:44 PM, Jagan Teki wrote:  
> >>> On Tue, Dec 4, 2018 at 5:56 PM Vignesh R <vigneshr@ti.com> wrote:  
> >>>>
> >>>> U-Boot SPI NOR support (sf layer) is quite outdated as it does not
> >>>> support 4 byte addressing opcodes, SFDP table parsing and different types of
> >>>> quad mode enable sequences. Many newer flashes no longer support BANK
> >>>> registers used by sf layer to a access >16MB space.
> >>>> Also, many SPI controllers have special MMIO interfaces which provide
> >>>> accelerated read/write access but require knowledge of flash parameters
> >>>> to make use of it. Recent spi-mem layer provides a way to support such
> >>>> flashes but sf layer isn't using that.
> >>>> This patch series syncs SPI NOR framework from Linux v4.19. It also adds
> >>>> spi-mem support on top.
> >>>> So, we gain 4byte addressing support and SFDP support. This makes
> >>>> migrating to U-Boot MTD framework easier.  
> >>>
> >>> We(someone) has proposed this sync before, but we(at-least I) rely on
> >>> implementing via DM not direct sync to Linux.  
> >>
> >> As I said in my cover letter, U-Boot sf layer is unable to support newer
> >> flashes mainly due to lack of 4 byte addressing and proper support for
> >> MMIO capable SPI controllers.
> >> My idea of fixing this is to borrow _features_ from Linux SPI NOR "as
> >> is". All that's needed is stateless 4 byte addressing, SFDP
> >> parsing(optionally), Quad/Octal support and spi-mem like abstraction for
> >> MMIO capable Controllers. I see no point in re-coding them from ground up.
> >>
> >> Could you be more specific on what you would like to see here in DM way?
> >> I have no issues in adapting this code to any framework here in U-Boot.
> >> Linux has driver model and SPI NOR subsystem is a framework and
> >> therefore any code ported from Linux will inherently have those
> >> abstractions. The only difference I see wrt your code in branch below vs
> >> this series is SPI-NOR uclass. This can be easily achieved by moving
> >> nor->ops out of struct spi_nor into uclass abstraction.
> >> Upstream Linux is anyways merging m25p80 and spi-nor so I did not see a
> >> need for SPI NOR uclass. I am okay to change that if you insist on
> >> having it.  
> > 
> > Merging or syncing spi-nor features stuff from Linux is good, I'm not
> > stopping that. but this can be do by satisfying u-boot driver-model
> > with proper architectural model. I know you take care but I'm not sure
> > ie what can be manageable for long term.
> > 
> > Let's discuss the proper architectural model, so-that we can move
> > further to incorporate the changes accordingly. (thanks at last we
> > have a thread to discuss)
> > 
> > Linux m25p80 is moved to spi-nor right? so does controllers on spi-nor
> > should be reside in same area like drivers/mtd/spi-nor or it should be
> > part of spi-mem. The last mail with  Boris, noted all spi-nor can't be
> > fit into spi-mem(sorry I lost the thread)
> >   
> 
> Yes, ATM all drivers fit into spi/spi-mem APIs and don't see any need
> for new spi-nor uclass
> 
> 
> > Example: we have zynq qspi it support BAR(with >16MB flashes), dual
> > qspi ect so does it comes under spi-mem or spi-nor?
> >   
> 
> In current mainline U-Boot, I see _no_ users of flags:
> SF_DUAL_STACKED_FLASH and SF_DUAL_PARALLEL_FLASH
> (I don't see flash->dual_flash set to any of the above enums).
> But if we do need to support such flashes in future, current address
> translation logic can be added to spi-nor.c (based on a DT flag), along
> with a way to pass this info via spi-mem ops.
> I would suggest to look at spi-mem ops (and in Linux mainline as well),
> if there are any shortcomings we can discuss here.
> 
> > So, if no driver should be part of spi-nor and all can be handle
> > spi-mem even-though they have controller specific features, yes we can
> > skip SPI_NOR_UCLASS otherwise we need spi-nor uclass that can be child
> > uclass of MTD.
> >   
> 
> In fact, after this series is merged, UCLASS_SPI_FLASH can be dropped
> and we can move to spi-nor(and sf_dataflash.c) directly under
> UCLASS_MTD. But, mostly likely would need to provide a lightweight MTD
> for SPL (similar to spi-nor-tiny.c) before that can be done.

That would be great!


Thanks,
Miquèl