[U-Boot] [RFC PATCH 00/20] SPI-NAND support

[Stefan Roese]

On 25.06.2018 16:55, Tom Rini wrote:
> On Mon, Jun 25, 2018 at 04:46:56PM +0200, Boris Brezillon wrote:
>> On Mon, 25 Jun 2018 19:58:37 +0530
>> Jagan Teki <jagan at amarulasolutions.com> wrote:
>>
>>>>>> - convert fsl-qspi to spi-mem
>>>>>
>>>>> We're not targeting the fsl-qspi controller here but a simple SPI
>>>>> controller that is already upstreamed. But yes, the fsl-qspi driver
>>>>> will have to be patched to support the spi-mem interface at some point.
>>>>
>>>> Can you point me that simple spi-mem controller driver?
>>
>> It's not a controller that implements spi-mem operations but a simple
>> SPI controller (one that knows how to do regular SPI transfers and
>> nothing more). But the spi-mem layer knows how to send spi_mem_op using
>> regular transfer and that's why it works without any modification at
>> the driver level.
>>
>>
>>>>>>
>>>>>> For spi-nor interface design, we have an example code here[2]
>>>>>>
>>>>>> I've paused this [2] series because of dm conversion of spi-drivers
>>>>>> otherwise I need add legacy code like mmc-legacy.c, so if we really
>>>>>> move to spi-mem design and okay with above design. I will try to move
>>>>>> the current spi flash to add MTD driver-model so-that we can add
>>>>>> spi-mem, spi-nand on top of it or we can work together to convert them
>>>>>> all.
>>>>>
>>>>> Why can't we do things iteratively. I mean, if the long term goal is to
>>>>> convert everything to the driver model, then this patchset is going in
>>>>> the right direction:
>>>>>   - addition of DM helpers to the MTD_UCLASS
>>>>>   - addition of the spi-mem interface properly integrated in the DM
>>>>>     model of the SPI framework
>>>>>   - addition of a SPI NAND driver, again properly integrated in the DM
>>>>>   - integration of DM-ready MTD drivers and old MTD drivers in a single
>>>>>     view exposed by the cmd/mtd.c command set
>>>>>
>>>>> I'd really like to limit the scope of this development to these topics,
>>>>> which doesn't prevent you from converting other part of u-boot to the
>>>>> spi-mem approach (SPI NOR is one example).
>>>>>
>>>>> I hope you understand our concerns and the fact that what you're asking
>>>>> us to do as a dependency of getting SPI NAND support + cmd/mtd.c merged
>>>>> is way more than we can actually provide.
>>>>
>>>> To answer all these questions, I think we need to decide whether we go
>>>> for MTD dm abstraction or existing MTD layer.
>>>>
>>>> When I say MTD dm abstraction, all mtd operation prototypes are in the
>>>> form of udevice unlike existing MTD has mtd_info. when I initially
>>>> supporting spi-nor (during Linux early spi-nor) I've reused existing
>>>> MTD and written something like what Miquel did using mtd_info ops [3].
>>>> but then developers on ML, proposed the new drivers should be form of
>>>> driver-model abstraction, so I've added mtd driver model ops [4].
>>>>
>>>> I understand the new MTD dm abstraction in U-Boot is not possible for
>>>> direct syncing from Linux, but we really want the u-boot way of
>>>> handling drivers and trying to copy code from Linux by removing
>>>> __UBOOT__ or any Linux specific macros. Since this is pretty much big
>>>> task, ie the reason I'm asking for single driver from each MTD device
>>>> so-that once the clear stack is ready other drivers can convert
>>>> one-by-one.
>>
>> I think I have to repeat my previous statement here. It would be very
>> unfortunate if u-boot decides to take this direction (see Richard's
>> reply), especially since I see absolutely no benefit in doing what you
>> suggest. Having MTD devices registered to the uboot DM is something I
>> can understand, deciding to no longer support the standard MTD API is
>> something I don't.
> 
> I agree.  We want U-Boot to be able to leverage as much as possible from
> the Linux kernel with as little re-working as possible.

I wholeheartedly agree on this.

Thanks,
Stefan