linux-kernel - Re: [PATCH 3/3] mtd: spi-nand: add devicetree binding

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Date:	Thu, 8 Jan 2015 12:12:20 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...tec.com>
To:	"Peter Pan 潘栋 (peterpandong)" 
	<peterpandong@...ron.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"Brian Norris" <computersforpeace@...il.com>
CC:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Qi Wang 王起 (qiwang)" 
	<qiwang@...ron.com>,
	"Frank Liu 刘群 (frankliu)" 
	<frankliu@...ron.com>,
	"Melanie Zhang 张燕 (melaniezhang)" <melaniezhang@...ron.com>
Subject: Re: [PATCH 3/3] mtd: spi-nand: add devicetree binding



On 01/08/2015 02:04 AM, Peter Pan 潘栋 (peterpandong) wrote:
>>> This commit adds the devicetree binding document that specifies the
>>> spi nand devices support.
>>>
>>> Signed-off-by: Peter Pan <peterpandong@...ron.com>
>>> ---
>>>  Documentation/devicetree/bindings/mtd/spi-nand.txt | 22
>> ++++++++++++++++++++++
>>>  1 file changed, 22 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/mtd/spi-
>> nand.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/mtd/spi-nand.txt
>> b/Documentation/devicetree/bindings/mtd/spi-nand.txt
>>> new file mode 100644
>>> index 0000000..9dd3efd
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/mtd/spi-nand.txt
>>> @@ -0,0 +1,22 @@
>>> +* NAND driver for MT29F, GD5F and similar SPI NAND flash chips
>>> +
>>> +Required properties:
>>> +- #address-cells, #size-cells : Must be present if the device has
>> sub-nodes
>>> +  representing partitions.
>>> +- compatible : Should be the manufacturer and the name of the chip.
>> Bear in mind
>>>
>>
>> Unless I'm mistaken, we don't need the chip ID here, as SPI NAND allows
>> to autodetect the device. Any reason why we can't just use a generic
>> compatible "spi-nand" here?
>> --
>> Ezequiel
> 
> In fact, I don't know how to autodetect the SPI NAND device. Micron device and
> Gigadevice device have different read ID functions. The Chip ID here is used to
> determine which function to use.
> 

Isn't the difference between the Read ID very minor? One of the vendor
needs a 2-byte ID read, and the other one needs a 3-byte ID read.

So you can just try with 2-byte, and if that fails (no vendor ID is
found on the first byte), you can try with the 3-byte command.

It's not the most elegant solution, but it's not super awful either.
-- 
Ezequiel
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