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 16:21:27 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Marek Vasut <marek.vasut@...il.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 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.

> 
> > 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.