[U-Boot] [PATCH v10 00/27] dm: Generic MTD Subsystem, with SPI-NOR interface

[Jagan Teki]

On Thu, Dec 28, 2017 at 8:14 PM, Lukasz Majewski <lukma at denx.de> wrote:
> Hi Jagan,
>
>> Compared to previous series’s [1], [2], [3] and [4] this patch set
>> redefined most of the implementation suitable to fit into existing
>> driver-model.
>>
>> MTD is generic subsystem for underlying flash devices like nand,
>> parallel nor, spinor, dataflash etc. So to drive this theory with
>> driver model(with an example of block layer) mtd is common device
>> interaction for most of  memory technology flashes like nand,
>> parallel nor, spinor, dataflash etc, these are treated as interface
>> types wrt u-boot driver model.
>>
>> Once the respective interface driver bind happen, the uclass driver
>> will pass an 'interface type' to mtd layer to create device for it,
>> for example once spinor ULASS_SPI_NOR driver bind happen,
>> the uclass driver of spinor will pass MTD_IF_TYPE_SPI_NOR
>> interface type to create mtd device for spinor devices.
>>
>> SPI-NOR:
>> =======
>> Some of the SPI device drivers at drivers/spi not a real
>> spi controllers, Unlike normal/generic SPI controllers they
>> operates only with SPI-NOR flash devices. these were technically
>> termed as SPI-NOR controllers, Ex: drivers/spi/fsl_qspi.c
>>
>> The problem with these were resides at drivers/spi is entire
>> SPI layer becomes SPI-NOR flash oriented which is absolutely
>> a wrong indication where SPI layer getting effected more with
>> flash operations - So this SPI-NOR core will resolve this issue
>> by separating all SPI-NOR flash operations from spi layer and
>> creats a generic layer called SPI-NOR core which can be used to
>> interact SPI-NOR to SPI driver interface layer and the SPI-NOR
>> controller driver.
>
> I must admit that I'm a bit confused....
>
> If you don't mind I would like to ask for clarification of a few things:
>
>
>
>>
>> =======================================
>>              cmd/spinor.c
>
>                 ^^^^^ - this would be a new set of commands to comply
>                 with DM?

with this series yes, and we're working on supporting the same with non-dm.

>
>                 What about "sf" command which we use now to get access
>                 to SPI-NOR memory? A lot of boards already use "sf"
>                 command... which may be tricky to replace.

end-goal will be replace sf with spinor command and removal of 'sf'
will be done when the new spi-nor framework stable enough to handle
all scenarios which are spi-flash supporting as of now.

>
>> =======================================
>>              mtd-uclass.c
>                 ^^^^^ - here we will have a generic MTD layer (as it is
>                 in Linux)

it is not like in Linux, leaving ops names apart all the code is for
creating mtd device for underlying flash devices in the form of
interface type during bind. the interface types as of now is spi-nor
it can be nand, nor, dataflash etc in future if could be.

>
>> =======================================
>>            spi-nor-uclass.c
>> =======================================
>>               spi-nor.c
>                 ^^^^^^ - why do we need to have spi-nor.c ? Cannot we
>                 have its functionality in the spi-nor-uclass.c ?
>                 (I'm just curious)

spi-nor-uclass.c is an uclass driver for underlying UCLASS_SPI_NOR
drivers like m25p80, zynq_qspinor etc but the spi-nor.c is the actual
spi-nor core code which handle actual flash specific stuff. and also
syncing Linux stuff(if require) becomes easy with spi-nor.c as a
separate file.

>
>> =======================================
>> m25p80.c                zynq_qspinor.c
>   ^^^^^ - this is the     ^^^^^^^^ - [*]
> "generic" spi-nor
> driver used in Linux.
> I suppose that it will
> be reused here?

yes - name reused because, I do think the Linux and U-Boot development
on spi-nor will follow in-line at some point but the most of code is
following U-Boot driver-model.

>
>> =======================================
>> spi-uclass.c
>   ^^^^^^^ - why do we
> need this uclass?

This is an existing uclass spi driver for underlying UCLASS_SPI
drivers like drivers/spi/zynq_qspi.c etc

>
>> =======================================
>> zynq_qspi.c
>  ^^^^^ - This is probably
> the low-level driver for
> zynq QSPI IP block - why
> do we have zynq_qspinor.c file above [*]?
> What is the difference/need of such division?

Both the drivers are same, the reason for zynq_qspinor is for testing
framework work for two directions like
- spi driver interface side through m25p80
cmd/spinor->mtd->spi-nor-uclass->spi-nor->m25p80->zynq_qspi.c
- direct spi-nor controller side
spinor->mtd->spi-nor-uclass->spi-nor->zynq_qspinor

Will remove drivers/spi/zynq_qspi.c once all set.

Jagan.

-- 
Jagan Teki
Free Software Engineer | www.openedev.com
U-Boot, Linux | Upstream Maintainer
Hyderabad, India.