linux-kernel - RE: [PATCH v1 2/2] arm64: dts: exynos: keep LDO12 always-on

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Message-ID: <02e601d653ad$a5734190$f059c4b0$@samsung.com>
Date:   Mon, 6 Jul 2020 21:23:49 +0530
From:   "Alim Akhtar" <alim.akhtar@...sung.com>
To:     "'Krzysztof Kozlowski'" <krzk@...nel.org>
Cc:     <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-samsung-soc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <robh+dt@...nel.org>
Subject: RE: [PATCH v1 2/2] arm64: dts: exynos: keep LDO12 always-on

Hi Krzysztof,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk@...nel.org>
> Sent: 05 July 2020 23:53
> To: Alim Akhtar <alim.akhtar@...sung.com>
> Cc: devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> samsung-soc@...r.kernel.org; linux-kernel@...r.kernel.org;
> robh+dt@...nel.org
> Subject: Re: [PATCH v1 2/2] arm64: dts: exynos: keep LDO12 always-on
> 
> On Sun, Jul 05, 2020 at 12:39:18PM +0530, Alim Akhtar wrote:
> > LDO12 on exynos7 supply power to VDDQ_UFS20_RESET, in case this
> > regulator is OFF, UFS host controller can not send command to UFS
> > device. To keep this supply ON, set regulator-always-on property for
> > this ldo.
> 
> Why UFS does not take any supplies? This looks like a workaround for the case
> of not implementing any consumer.
> 
This particular supply is not part of UFS HCI spec and binding documentation, as per binding only one supply for host controller and three others for UFS device are needed. My best guess is, VDDQ_UFS20_RESET supply to reset logic block inside HCI, which might be specific to this controller version (I did not find any such supply in the latest host controller though).

> Best regards,
> Krzysztof
> 
> 
> >
> > Signed-off-by: Alim Akhtar <alim.akhtar@...sung.com>
> > ---
> >  arch/arm64/boot/dts/exynos/exynos7-espresso.dts | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/exynos/exynos7-espresso.dts
> > b/arch/arm64/boot/dts/exynos/exynos7-espresso.dts
> > index bb86950032d3..92fecc539c6c 100644
> > --- a/arch/arm64/boot/dts/exynos/exynos7-espresso.dts
> > +++ b/arch/arm64/boot/dts/exynos/exynos7-espresso.dts
> > @@ -194,6 +194,7 @@
> >  				regulator-min-microvolt = <1000000>;
> >  				regulator-max-microvolt = <1300000>;
> >  				regulator-enable-ramp-delay = <125>;
> > +				regulator-always-on;
> >  			};
> >
> >  			ldo13_reg: LDO13 {
> > --
> > 2.17.1
> >