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 23:29:00 +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 11:25 PM, Boris Brezillon wrote:
> On Mon, 19 Nov 2018 23:22:45 +0100
> Marek Vasut <marek.vasut@...il.com> wrote:
> 
>> 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.
>>
> 
> No, spi-mem controller drivers should go in drivers/spi/ even if they
> don't implement the generic SPI interface (it's allowed to only
> implement the spi_mem interface).

Except this is not only SPI MEM controller, this is also hyperflash
(that is, CFI) controller. It can drive both types of chips. Thus , I
think it fits better in drivers/mtd/ .

-- 
Best regards,
Marek Vasut