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 23:25:17 +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 23:22:45 +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).

>