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 16:12:41 +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 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).

> 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.

-- 
Best regards,
Marek Vasut