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

[Vignesh R]

On 10-Dec-18 6:32 PM, Jagan Teki wrote:
> On Thu, Dec 6, 2018 at 11:55 PM Vignesh R <vigneshr at 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 at 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 U-Boot SPI NOR support (sf layer) is quite outdated as it does not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.

Regards
Vignesh