linux-kernel - Re: [PATCH 1/6] ARM: dts: dra7-evm: Make VDDA_1V8

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Date:	Wed, 2 Jul 2014 17:37:00 +0300
From:	Roger Quadros <rogerq@...com>
To:	Nishanth Menon <nm@...com>, <tony@...mide.com>, <kishon@...com>,
	<balbi@...com>
CC:	<nsekhar@...com>, <george.cherian@...com>,
	<linux-omap@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Rajendra Nayak <rnayak@...com>,
	Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH 1/6] ARM: dts: dra7-evm: Make VDDA_1V8_PHY supply always
 on

On 07/02/2014 04:05 PM, Nishanth Menon wrote:
> On 07/02/2014 07:03 AM, Roger Quadros wrote:
>> After clarification from the hardware team it was found that
>> this 1.8V PHY supply can't be switched OFF when SoC is Active.
>> It can only be switched off when in PORz (power on reset).
> 
> I dont think folks know the reasoning why hardware team decided that
> the voltage rail cannot be switched off -> I suggest adding the
> following information as well.
> 
> Since isolation is not present in the design for these PHY IPs to
> allow for the PHY rail to be switched off, there is a very high risk
> of IP reliability and additional leakage paths which can result in
> additional power consumption.
> 
> Only scenario where this rail can be switched off is part of Power on
> reset sequencing, but it needs to be kept always-on during operation.

This sort of information should be in the TRM instead, but doesn't harm to be in the commit message so I'll do that.
Thanks.

cheers,
-roger
> 
>>
>> This patch is required for proper functionality of USB, SATA
>> and PCIe on DRA7-evm.
>>
>> CC: Rajendra Nayak <rnayak@...com>
>> CC: Tero Kristo <t-kristo@...com>
>> Signed-off-by: Roger Quadros <rogerq@...com>
>> ---
>>  arch/arm/boot/dts/dra7-evm.dts | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm/boot/dts/dra7-evm.dts b/arch/arm/boot/dts/dra7-evm.dts
>> index 4adc280..8308954 100644
>> --- a/arch/arm/boot/dts/dra7-evm.dts
>> +++ b/arch/arm/boot/dts/dra7-evm.dts
>> @@ -240,6 +240,7 @@
>>  					regulator-name = "ldo3";
>>  					regulator-min-microvolt = <1800000>;
>>  					regulator-max-microvolt = <1800000>;
>> +					regulator-always-on;
>>  					regulator-boot-on;
>>  				};
>>  
>>
> 
> 

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