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

[Vignesh R]

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 U-Boot SPI NOR support (sf layer) is quite outdated as it does not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.


> ofcourse other
> subsystems might have doing this but I literally don't propose to do
> that, since it may fire the u-boot implementation in future.
> 

Could you explain what might be possible issues in future? I will work
on it.

> If you really get things up further, try to check this DM based
> spi-nor here[1] and lets discuss on u-boot point-of-view. I've paused
> this because of non-dm code, but I'm thinking we even re-change this
> to fit MTD driver-model (this is my TODO, once spi dm migration done).
> 
AFAICS, Non DM code is not going away anytime soon. Meanwhile, IMHO,
lack of 4 byte addressing support is significantly hampering new
development (as evident from number of people trying to add 4 byte
addressing support.)

> [1] http://git.denx.de/?p=u-boot-spi.git;a=shortlog;h=refs/heads/next-working
> 

IIRC, last post of this branch was in January 2018. And looking at my
inbox, its seems that 4 byte addressing was broken in that series.
If you add 4 byte addressing + SFDP parsing logic + spi-mem support to
above branch, I am pretty sure you spi-nor.c would look almost the same
to whats there in this series.

Regards
Vignesh