Re: [PATCH v5 2/3] spi: dt-bindings: Describe stacked/parallel memories modes

[<Tudor.Ambarus@microchip.com>]

On 12/22/21 10:05 AM, Miquel Raynal wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hello Tudor,

Hi!

> 
> Tudor.Ambarus@microchip.com wrote on Wed, 22 Dec 2021 07:52:44 +0000:
> 
>> On 12/21/21 7:00 PM, Miquel Raynal wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> Describe two new memories modes:
>>> - A stacked mode when the bus is common but the address space extended
>>>   with an additinals wires.
>>> - A parallel mode with parallel busses accessing parallel flashes where
>>>   the data is spread.
>>>
>>> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
>>> ---
>>>
>>> Hello Rob,
>>>
>>> I know the below does not pass the tests (at least the example patch 3
>>> does not pass) but I believe the issue is probably on the tooling side
>>> because the exact same thing with uing32-array instead is accepted. The
>>> problem comes from the minItems/maxItems lines. Without them, this is
>>> okay. The maxItems btw matches the "good enough value for now" idea.
>>>
>>> The errors I get are:
>>>
>>> $ make dt_binding_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/spi/spi-controller.yaml
>>>   LINT    Documentation/devicetree/bindings
>>>   CHKDT   Documentation/devicetree/bindings/processed-schema-examples.json
>>>   SCHEMA  Documentation/devicetree/bindings/processed-schema-examples.json
>>>   DTEX    Documentation/devicetree/bindings/spi/spi-controller.example.dts
>>>   DTC     Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml
>>>   CHECK   Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml
>>> /src/Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml: spi@80010000: flash@2:stacked-memories: [[268435456, 268435456]] is too short
>>>         From schema: /src/Documentation/devicetree/bindings/spi/spi-controller.yaml
>>> /src/Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml: spi@80010000: flash@2:stacked-memories: [[268435456, 268435456]] is too short
>>>         From schema: /src/Documentation/devicetree/bindings/spi/mxs-spi.yaml
>>> /src/Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml: spi@80010000: Unevaluated properties are not allowed ('#address-cells', '#size-cells', 'display@0', 'sensor@1', 'flash@2' were unexpected)
>>>         From schema: /src/Documentation/devicetree/bindings/spi/mxs-spi.yaml
>>> /src/Documentation/devicetree/bindings/spi/spi-controller.example.dt.yaml: flash@2: stacked-memories: [[268435456, 268435456]] is too short
>>>         From schema: /src/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
>>>
>>>
>>>  .../bindings/spi/spi-peripheral-props.yaml    | 25 +++++++++++++++++++
>>>  1 file changed, 25 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> index 5dd209206e88..fedb7ae98ff6 100644
>>> --- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> +++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> @@ -82,6 +82,31 @@ properties:
>>>      description:
>>>        Delay, in microseconds, after a write transfer.
>>>
>>> +  stacked-memories:
>>> +    description: Several SPI memories can be wired in stacked mode.
>>> +      This basically means that either a device features several chip
>>> +      selects, or that different devices must be seen as a single
>>> +      bigger chip. This basically doubles (or more) the total address
>>> +      space with only a single additional wire, while still needing
>>> +      to repeat the commands when crossing a chip boundary. The size of
>>> +      each chip should be provided as members of the array.
>>> +    $ref: /schemas/types.yaml#/definitions/uint64-array
>>> +    minItems: 2
>>> +    maxItems: 4
>>
>> Why do we define maxItems? Can't we remove this restriction?
> 
> Rob usually prefers to bound properties, that's why we often see "good
> enough values for now" in the bindings. If it's no longer the case it's

right, I saw it.

> fine to drop the maxItems property.

There's no such hardware limitation as far as I know, that's why I've
asked. Maybe Rob can advise.

Cheers,
ta

> 
>>> +
>>> +  parallel-memories:
>>> +    description: Several SPI memories can be wired in parallel mode.
>>> +      The devices are physically on a different buses but will always
>>> +      act synchronously as each data word is spread across the
>>> +      different memories (eg. even bits are stored in one memory, odd
>>> +      bits in the other). This basically doubles the address space and
>>> +      the throughput while greatly complexifying the wiring because as
>>> +      many busses as devices must be wired. The size of each chip should
>>> +      be provided as members of the array.
>>> +    $ref: /schemas/types.yaml#/definitions/uint64-array
>>> +    minItems: 2
>>> +    maxItems: 4
>>> +
>>>  # The controller specific properties go here.
>>>  allOf:
>>>    - $ref: cdns,qspi-nor-peripheral-props.yaml#
>>> --
>>> 2.27.0
>>>
>>
> 
> 
> Thanks,
> Miquèl
>