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 23:22:45 +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 11:19 PM, Boris Brezillon wrote:
> On Mon, 19 Nov 2018 23:11:31 +0100
> Marek Vasut <marek.vasut@...il.com> wrote:
> 
>> 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 ?
>>
> 
> The spi-mem layer is in drivers/spi/ so it could go in drivers/spi/
> (spi-mem controller) or drivers/mtd/ (CFI controller).

drivers/mtd is probably a better option, since it's not a generic SPI
controller.


-- 
Best regards,
Marek Vasut