linux-kernel - Re: [PATCH 4/5] pwm: pwm-tipwmss: Update documentation to use empty range property

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Date:	Thu, 17 Mar 2016 11:56:29 -0500
From:	"Franklin S Cooper Jr." <fcooper@...com>
To:	Rob Herring <robh@...nel.org>
CC:	<thierry.reding@...il.com>, <pawel.moll@....com>,
	<mark.rutland@....com>, <ijc+devicetree@...lion.org.uk>,
	<galak@...eaurora.org>, <bcousson@...libre.com>,
	<tony@...mide.com>, <linux@....linux.org.uk>, <t-kristo@...com>,
	<mturquette@...libre.com>, <sboyd@...eaurora.org>,
	<linux-pwm@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-clk@...r.kernel.org>
Subject: Re: [PATCH 4/5] pwm: pwm-tipwmss: Update documentation to use empty
 range property



On 03/17/2016 10:01 AM, Rob Herring wrote:
> On Mon, Mar 07, 2016 at 01:51:57PM -0600, Franklin S Cooper Jr wrote:
>> Since the PWMSS and its subdevices (eCAP and ePWM) use the same address
>> space then the range property should be empty. Update the documentation
>> to show the correct usage.
> Why does it matter? An empty ranges is generally not preferred.

Someone pointed out that ranges should probably be empty. I
double checked it with what is in the ePAPR doc and based on
the definition it should be set to empty. I also checked
against the am33xx.dtsi and saw that both USB and ethernet
uses an empty value for ranges.

Can you elaborate on why this isn't preferable?

>
>> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
>> ---
>>  Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt | 12 ++++--------
>>  1 file changed, 4 insertions(+), 8 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt b/Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt
>> index f7eae77..672fa71 100644
>> --- a/Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt
>> +++ b/Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt
>> @@ -7,11 +7,9 @@ Required properties:
>>  		  Should set to 1.
>>  - size-cells: specify number of u32 entries needed to specify child nodes size
>>  		in reg property. Should set to 1.
>> -- ranges: describes the address mapping of a memory-mapped bus. Should set to
>> -	   physical address map of child's base address, physical address within
>> -	   parent's address  space and length of the address map. For am33xx,
>> -	   3 set of child register maps present, ECAP register space, EQEP
>> -	   register space, EHRPWM register space.
>> +- ranges: describes the address mapping of a memory-mapped bus. Its value
>> +	  should be empty since no address translation is needed between the
>> +	  parent and the child.
>>  
>>  Also child nodes should also populated under PWMSS DT node.
>>  
>> @@ -23,9 +21,7 @@ pwmss0: pwmss@...00000 {
>>  	#address-cells = <1>;
>>  	#size-cells = <1>;
>>  	status = "disabled";
>> -	ranges = <0x48300100 0x48300100 0x80   /* ECAP */
>> -		  0x48300180 0x48300180 0x80   /* EQEP */
>> -		  0x48300200 0x48300200 0x80>; /* EHRPWM */
>> +	ranges;
>>  
>>  	/* child nodes go here */
>>  };
>> -- 
>> 2.7.0
>>