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 23:19:54 +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 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). Looks like you
didn't closely follow what has happened in the spi-nor subsystem
lately :P.