linux-kernel - Re: [PATCH v2 2/2] doc: dt: mtd: add a DT property to enable the use of 4byte-address op codes

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Date:	Wed, 23 Mar 2016 16:08:58 +0100
From:	Cyrille Pitchen <cyrille.pitchen@...el.com>
To:	Rob Herring <robh+dt@...nel.org>,
	Brian Norris <computersforpeace@...il.com>
CC:	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"Nicolas Ferre" <nicolas.ferre@...el.com>,
	boris brezillon <boris.brezillon@...e-electrons.com>,
	Marek Vašut <marex@...x.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>
Subject: Re: [PATCH v2 2/2] doc: dt: mtd: add a DT property to enable the use
 of 4byte-address op codes

Hi Rob,

sorry I've sent v3 at the same time as you answered to v2.
I'll take your comments into account for v4.

Brian, any preference between 4byte-opcodes or m25p-4byte-opcodes?

Best regards,

Cyrille

Le 23/03/2016 13:49, Rob Herring a écrit :
> On Tue, Mar 22, 2016 at 10:13 AM, Cyrille Pitchen
> <cyrille.pitchen@...el.com> wrote:
>> This patch adds a new optional DT property which enables an alternative
>> way of supporting memory size above 16MiB (128Mib). This new mechanism
>> translates the regular 3byte-address op codes into their 4byte-address
>> version whereas the old/default mecanism makes the SPI memory enter its
>> 4byte-address mode, which has annoying side effects for early bootloaders.
>>
>> We cannot discover at run time whether the SPI NOR memory supports the
>> 4byte-address op codes. For instance both Macronix MX25L25635E and
>> MX25L25673G share the same JEDEC ID (C22019 without any extension byte).
>> However the first one doesn't support 4byte-address op codes whereas the
>> second one does.
>>
>> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
>> ---
>>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
>> index 2c91c03e7eb0..8be610482089 100644
>> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
>> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
>> @@ -66,6 +66,17 @@ Optional properties:
>>                     Refer to your chips' datasheet to check if this is supported
>>                     by your chip.
>>
>> +- m25p,4byte-opcodes: For memory size above 16MiB (128Mib), use the dedicated
> 
> m25p is not a vendor. So drop it or m25p-4byte-opcodes.
> 
>> +                      4byte-address opcodes instead of entering the 4byte
>> +                      address mode. This mode changes the internal state of the
>> +                      chip so may conflict with some early boot loaders, which
>> +                      expect to use the regular (Fast) Read opcodes with 3byte
>> +                      address.
>> +                      However 4byte-address opcodes are not supported by all
>> +                      chips and support for them can not be detected at runtime.
> 
> s/can not/cannot/
> 
>> +                      Refer to you chip's datasheet to check if this is
>> +                      supported by your chip.
>> +
>>  Example:
>>
>>         flash: m25p80@0 {
>> --
>> 1.8.2.2
>>