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

[Cyrille Pitchen]

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 at atmel.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 at atmel.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 at 0 {
>> --
>> 1.8.2.2
>>