linux-kernel - Re: [PATCH 2/2] memory: ti-aemif: add bindings for AEMIF driver

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Date:	Fri, 29 Nov 2013 10:10:44 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>
CC:	Kumar Gala <galak@...nel.crashing.org>,
	"ivan.khoronzhuk" <ivan.khoronzhuk@...com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	devicetree <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <rob.herring@...xeda.com>,
	<linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] memory: ti-aemif: add bindings for AEMIF driver

On Friday 29 November 2013 10:00 AM, Grygorii Strashko wrote:
> Hi Kumar Gala,
> 
> On 11/22/2013 11:06 PM, Kumar Gala wrote:
>>
>> On Nov 20, 2013, at 1:03 PM, ivan.khoronzhuk <ivan.khoronzhuk@...com> wrote:
>>
>>> On 11/20/2013 08:21 PM, Jean-Christophe PLAGNIOL-VILLARD wrote:
>>>>> +				the chip select signal.
>>>>> +				Minimum value is 1 (0 treated as 1).
>>>>> +
>>>>> +- ti,cs-wsetup:		write setup width, ns
>>>>> +				Time between the beginning of a memory cycle
>>>>> +				and the activation of write strobe.
>>>>> +				Minimum value is 1 (0 treated as 1).
>>>>> +
>>>>> +- ti,cs-wstrobe:	write strobe width, ns
>>>>> +				Time between the activation and deactivation of
>>>>> +				the write strobe.
>>>>> +				Minimum value is 1 (0 treated as 1).
>>>>> +
>>>>> +- ti,cs-whold:		write hold width, ns
>>>>> +				Time between the deactivation of the write
>>>>> +				strobe and the end of the cycle (which may be
>>>>> +				either an address change or the deactivation of
>>>>> +				the chip select signal.
>>>>> +				Minimum value is 1 (0 treated as 1).
>>>>> +
>>>>> +If any of the above parameters are absent, current parameter value will be taken
>>>>> +from the corresponding HW reg.
>>>>> +
>>>>> +The name for cs node must be in format csN, where N is the cs number.
>>>>
>>>> this is wired we should use reg instead to represent the cs as done for SPI
>>>> or a an other property
>>>>
>>>> Best Regards,
>>>> J.
>>>>
>>>
>>> Ok, I will add new property cs-chipselect like following :
>>>
>>> ti,cs-chipselect:	number of chipselect. Indicates on the
>>> 			aemif driver which chipselect is used
>>> 			for accessing the memory.
>>> 			For compatibles "ti,davinci-aemif" and
>>> 			"ti,keystone-aemif" it can be in range [0-3].
>>> 			For compatible "ti,omap-L138-aemif" range is [2-5].
>>>
>>> Is it OK?
>>
>> Why do you need this? As it was mentioned just use reg:
>>
>> So you’d have something like:
>>
>> memory-controller@...00A00 {
>> 	…
>> 	nand:cs2@2 {
>> 		reg = <2 0 0>;
>> 		ranges;
>> 		...
>>
>> 	}:
>> };
> 
> I'd prefer to continue with "ti,cs-chipselect" (this is more human friendly definition, as for me),
> but if you insist - it can be changed as:
> memory-controller@...00A00 {
> 	compatible = "ti,keystone-aemif";
> ...
> 
> 	cs2 {
> 		compatible = "ti,aemif-cs";
> 		reg = <2>;
> ...
> 	}
> 
> 	cs0 {
> 		compatible = "ti,aemif-cs";
> 		reg = <0>;
> ...
> 	}
> 
>>
>> However, I’m confused by the example in which you have:
>>
>> +		nand@0,0x8000000 {
>> +			compatible = "ti,davinci-nand";
>> +			reg = <0 0x8000000 0x4000000
>> +			       1 0x0000000 0x0000100>;
>> +
>> +			.. see davinci-nand.txt
>> +		};
>>
>> What chipselects is this on 0 & 1?
> 
> As I described in https://lkml.org/lkml/2013/11/26/282 we are not encoding CS number in reg
>  - it's memory partition number.
> 
> Also, I'd like to note that we *DO NOT introduce* NAND device bindings here.
> The Davinci NAND bindings was introduced and accepted more then one year ago, and
> we've just updated its a bit (keeping full compatibility) and reused
> (see https://lkml.org/lkml/2013/11/21/182). 
> And the CS number is encoded for Davinci NAND node using standalone property
> "ti,davinci-chipselect" and we need to provide (2) two memory ranges to it,
> as result we can't encode CS number in "reg" for AEMIF child devices (NAND/NOR/etc),
> as it will break bindings compatibility.
> 
> In this document, NAND node is used just as an example of child node.
> 
The above should have been really captured in the commit log to get a better
picture. No way on earth, a reviewer can figure out whether this is new bindings
or copy of bindings already used.

Regards,
Santosh

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