linux-kernel - Re: [PATCH 2/2] dt-binding: spi: Document Renesas R-Car RPC controller bindings

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Date:   Mon, 19 Nov 2018 23:11:31 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Mason Yang <masonccyang@...c.com.tw>, broonie@...nel.org,
        tpiepho@...inj.com, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Simon Horman <horms@...ge.net.au>, juliensu@...c.com.tw,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        zhengxunli@...c.com.tw
Subject: Re: [PATCH 2/2] dt-binding: spi: Document Renesas R-Car RPC
 controller bindings

On 11/19/2018 04:21 PM, Boris Brezillon wrote:
> On Mon, 19 Nov 2018 16:12:41 +0100
> Marek Vasut <marek.vasut@...il.com> wrote:
> 
>> On 11/19/2018 03:43 PM, Boris Brezillon wrote:
>>> On Mon, 19 Nov 2018 15:14:07 +0100
>>> Marek Vasut <marek.vasut@...il.com> wrote:
>>>   
>>>> On 11/19/2018 03:10 PM, Boris Brezillon wrote:  
>>>>> On Mon, 19 Nov 2018 14:49:31 +0100
>>>>> Marek Vasut <marek.vasut@...il.com> wrote:
>>>>>     
>>>>>> On 11/19/2018 11:01 AM, Mason Yang wrote:    
>>>>>>> Document the bindings used by the Renesas R-Car D3 RPC controller.
>>>>>>>
>>>>>>> Signed-off-by: Mason Yang <masonccyang@...c.com.tw>
>>>>>>> ---
>>>>>>>  .../devicetree/bindings/spi/spi-renesas-rpc.txt    | 33 ++++++++++++++++++++++
>>>>>>>  1 file changed, 33 insertions(+)
>>>>>>>  create mode 100644 Documentation/devicetree/bindings/spi/spi-renesas-rpc.txt
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/spi/spi-renesas-rpc.txt b/Documentation/devicetree/bindings/spi/spi-renesas-rpc.txt
>>>>>>> new file mode 100644
>>>>>>> index 0000000..8286cc8
>>>>>>> --- /dev/null
>>>>>>> +++ b/Documentation/devicetree/bindings/spi/spi-renesas-rpc.txt
>>>>>>> @@ -0,0 +1,33 @@
>>>>>>> +Renesas R-Car D3 RPC controller Device Tree Bindings
>>>>>>> +----------------------------------------------------
>>>>>>> +
>>>>>>> +Required properties:
>>>>>>> +- compatible: should be "renesas,rpc-r8a77995"
>>>>>>> +- #address-cells: should be 1
>>>>>>> +- #size-cells: should be 0
>>>>>>> +- reg: should contain 2 entries, one for the registers and one for the direct
>>>>>>> +       mapping area
>>>>>>> +- reg-names: should contain "rpc_regs" and "dirmap"
>>>>>>> +- interrupts: interrupt line connected to the RPC SPI controller      
>>>>>>
>>>>>> Do you also plan to support the RPC HF mode ? And if so, how would that
>>>>>> look in the bindings ?    
>>>>>
>>>>> Not sure this approach is still accepted, but that's how we solved the
>>>>> problem for the flexcom block [1].
>>>>>
>>>>> [1]https://elixir.bootlin.com/linux/v4.20-rc3/source/Documentation/devicetree/bindings/mfd/atmel-flexcom.txt    
>>>>
>>>> That looks pretty horrible.
>>>>
>>>> In U-Boot we check whether the device hanging under the controller node
>>>> is JEDEC SPI flash or CFI flash and based on that decide what the config
>>>> of the controller should be (SPI or HF). Not sure that's much better,but
>>>> at least it doesn't need extra nodes which do not really represent any
>>>> kind of real hardware.
>>>>  
>>>
>>> The subnodes are not needed, you can just have a property that tells in
>>> which mode the controller is supposed to operate, and the MFD would
>>> create a sub-device that points to the same device_node.  
>>
>> Do you even need a dedicated property ? I think you can decide purely on
>> what node is hanging under the controller (jedec spi nor or cfi nor).
> 
> Yes, that could work if they have well-known compatibles. As soon as
> people start using flash-specific compats (like some people do for
> their SPI NORs) it becomes a maintenance burden.

Which, on this controller, is very likely never gonna happen. Once it
does , we can add a custom property.

>>> Or we can have
>>> a single driver that decides what to declare (a spi_controller or flash
>>> controller), but you'd still have to decide where to place this
>>> driver...  
>>
>> I'd definitely prefer a single driver.
>>
> 
> Where would you put this driver? I really don't like the idea of having
> MTD drivers spread over the tree. Don't know what's Mark's opinion on
> this matter.

Well, it's both CFI (hyperflash) and SF (well, SPI flash) controller, so
where would this go ?

-- 
Best regards,
Marek Vasut