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

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Date:	Wed, 2 Jul 2014 08:05:51 -0500
From:	Nishanth Menon <nm@...com>
To:	Roger Quadros <rogerq@...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 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 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;
>  				};
>  
> 


-- 
Regards,
Nishanth Menon
--
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