linux-kernel - Re: [PATCH] mtd: nand: denali: allow to override max

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Message-ID: <CAK7LNATqVEMRwa+Ss4V9sBXYZwqKX=CpB_3Oox8bM6Yow0mkXA@mail.gmail.com>
Date:	Sat, 26 Mar 2016 13:27:50 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	linux-mtd@...ts.infradead.org,
	Graham Moore <grmoore@...nsource.altera.com>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	devicetree@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Richard Weinberger <richard@....at>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Brian Norris <computersforpeace@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] mtd: nand: denali: allow to override max_banks from DT property

2016-03-25 23:45 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> On Thu, 24 Mar 2016 21:24:37 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>> Commit 271707b1d817 ("mtd: nand: denali: max_banks calculation
>> changed in revision 5.1") supported the new encoding of the "n_banks"
>> bits of the "features" register, but there is an unfortunate case
>> that is not covered by that commit.
>>
>> Panasonic (its System LSI division is now Socionext) bought several
>> versions of this IP.  The IP released for Panasonic around Feb. 2012
>> is revision 5 and uses the old encoding for n_banks (2 << n_banks).
>> While the one released around Nov. 2012 is also revision 5, but it
>> uses the new encoding (1 << n_banks).
>>
>> The revision register cannot distinguish these two incompatible
>> hardware.  I guess this IP series is not well-organized.  I could not
>> find any alternative but giving max_banks from DT property.
>
> Hm, shouldn't that be addressed with a new compatible instead of adding
> a extra property?
>
>>
>> This commit works around the problem by allowing DT to set the
>> max_banks forcibly.  Of course, this DT property can be optional if
>> the auto detection based on the hardware registers works well.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>>
>>  Documentation/devicetree/bindings/mtd/denali-nand.txt | 4 ++++
>>  drivers/mtd/nand/denali.c                             | 3 ++-
>>  drivers/mtd/nand/denali_dt.c                          | 3 +++
>>  3 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/mtd/denali-nand.txt b/Documentation/devicetree/bindings/mtd/denali-nand.txt
>> index 785b825..78c250d 100644
>> --- a/Documentation/devicetree/bindings/mtd/denali-nand.txt
>> +++ b/Documentation/devicetree/bindings/mtd/denali-nand.txt
>> @@ -7,6 +7,10 @@ Required properties:
>>    - interrupts : The interrupt number.
>>    - dma-mask : DMA bit mask
>>
>> +Optional properties:
>> +  - max-banks : Maximum number of banks supported by hardware.  If not
>> +    specified, it is determined based on the "features" register of hardware.
>> +
>
> You might want to prefix that with "denali,".
>
>>  The device tree may optionally contain sub-nodes describing partitions of the
>>  address space. See partition.txt for more detail.


In which case, do we have to add a vendor prefix to DT properties?

I do not know a clear rule about this.


-- 
Best Regards
Masahiro Yamada