linux-kernel - Re: [PATCH v4 06/10] dt-bindings: mtd: update STM32 FMC2 NAND controller documentation

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Message-ID: <3c860c17-f8dd-6130-861b-afccb9202093@st.com>
Date:   Fri, 15 May 2020 11:02:36 +0200
From:   Christophe Kerello <christophe.kerello@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Miquèl Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh R <vigneshr@...com>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <devicetree@...r.kernel.org>,
        Marek Vašut <marex@...x.de>
Subject: Re: [PATCH v4 06/10] dt-bindings: mtd: update STM32 FMC2 NAND
 controller documentation

Hi Rob,

On 5/14/20 7:55 PM, Rob Herring wrote:
> On Thu, May 14, 2020 at 11:35 AM Christophe Kerello
> <christophe.kerello@...com> wrote:
>>
>> Hi Rob,
>>
>> On 5/14/20 5:00 PM, Rob Herring wrote:
>>> On Wed, May 06, 2020 at 11:11:15AM +0200, Christophe Kerello wrote:
>>>> These bindings can be used on SOCs where the FMC2 NAND controller is
>>>> in standalone. In case that the FMC2 embeds 2 controllers (an external
>>>> bus controller and a raw NAND controller), the register base and the
>>>> clock will be defined in the parent node. It is the reason why the
>>>> register base address and the clock are now optional.
>>>>
>>>> Signed-off-by: Christophe Kerello <christophe.kerello@...com>
>>>> ---
>>>>    .../devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml   | 19 ++++++++++---------
>>>>    1 file changed, 10 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml b/Documentation/devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml
>>>> index b059267..68fac1a 100644
>>>> --- a/Documentation/devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml
>>>> +++ b/Documentation/devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml
>>>> @@ -18,13 +18,15 @@ properties:
>>>>
>>>>      reg:
>>>>        items:
>>>> -      - description: Registers
>>>> +      - description: Registers (optional)
>>>
>>> The only thing that can be optional are the last entries. You have to do
>>> a 'oneOf' with 6 entries and 7 entries.
>>
>> Ok, so the way to describe the reg property in my case should be:
>>          reg:
>>            oneOf:
>>              - description: FMC2 embeds the NFC controller in standalone.
>>                items:
>>                  - description: Registers
>>                  - description: Chip select 0 data
>>                  - description: Chip select 0 command
>>                  - description: Chip select 0 address space
>>                  - description: Chip select 1 data
>>                  - description: Chip select 1 command
>>                  - description: Chip select 1 address space
>>
>>              - description: FMC2 embeds the NFC controller and the EBI
>>                  controller.
>>                items:
>>                  - description: Chip select 0 data
>>                  - description: Chip select 0 command
>>                  - description: Chip select 0 address space
>>                  - description: Chip select 1 data
>>                  - description: Chip select 1 command
>>                  - description: Chip select 1 address space
>>
>>>
>>> And where's your new compatible string for this different h/w?
>>
>>   From NFC controller point of view, it is the same HW.
> 
> That's what everyone says until they have some quirk or integration
> difference to handle.
> 
>> In the case that we have 2 controllers embedded, the register base is
>> shared.
>> The NFC driver will check at probe time the compatible string of its
>> parent node.
>> In case that it is "st,stm32mp1-fmc2-ebi", then the driver will find the
>> register base in the parent node (EBI node), otherwise it will find it
>> in the NFC node.
>> Is it better to have 2 compatible strings (one for each reg description)
>> than checking the parent's compatible string and have only one
>> compatible string?
> 
> Why not just put the register base into the child node too? While
> overlapping 'reg' regions for siblings is bad, it's fine for child
> nodes. I guess since there are chip selects for the child nodes that
> may not work here.
> 
> It doesn't hurt to have another compatible. You can always make the
> old one a fallback. With different compatibles you can make sure reg
> has the right number of entries.
> 
> Rob
> 

I will add a new compatible string to handle the reg property.
It will be part of v5.

Regards,
Christophe Kerello.