Re: [PATCH] arm64: dts: imx8mp: Describe VDD_ARM run and standby voltage for Data Modul i.MX8M Plus eDM SBC

[Shawn Guo <shawnguo@kernel.org>]

On Mon, Oct 09, 2023 at 04:03:01PM +0200, Marek Vasut wrote:
> On 10/9/23 14:36, Shawn Guo wrote:
> > On Sun, Oct 08, 2023 at 08:37:34PM +0200, Marek Vasut wrote:
> > > On 9/24/23 16:21, Shawn Guo wrote:
> > > > On Thu, Aug 31, 2023 at 08:18:50PM +0200, Marek Vasut wrote:
> > > > > Describe VDD_ARM (BUCK2) run and standby voltage in DT.
> > > > > 
> > > > > Signed-off-by: Marek Vasut <marex@denx.de>
> > > > > ---
> > > > > Cc: Conor Dooley <conor+dt@kernel.org>
> > > > > Cc: Fabio Estevam <festevam@gmail.com>
> > > > > Cc: Frieder Schrempf <frieder.schrempf@kontron.de>
> > > > > Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> > > > > Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
> > > > > Cc: Magnus Damm <magnus.damm@gmail.com>
> > > > > Cc: Marek Vasut <marex@denx.de>
> > > > > Cc: NXP Linux Team <linux-imx@nxp.com>
> > > > > Cc: Peng Fan <peng.fan@nxp.com>
> > > > > Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
> > > > > Cc: Rob Herring <robh+dt@kernel.org>
> > > > > Cc: Sascha Hauer <s.hauer@pengutronix.de>
> > > > > Cc: Shawn Guo <shawnguo@kernel.org>
> > > > > Cc: devicetree@vger.kernel.org
> > > > > Cc: linux-arm-kernel@lists.infradead.org
> > > > > ---
> > > > >    arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts | 2 ++
> > > > >    1 file changed, 2 insertions(+)
> > > > > 
> > > > > diff --git a/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts b/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts
> > > > > index 13674dc64be9d..d98a040860a48 100644
> > > > > --- a/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts
> > > > > +++ b/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts
> > > > > @@ -362,6 +362,8 @@ buck1: BUCK1 {	/* VDD_SOC (dual-phase with BUCK3) */
> > > > >    			};
> > > > >    			buck2: BUCK2 {	/* VDD_ARM */
> > > > > +				nxp,dvs-run-voltage = <950000>;
> > > > > +				nxp,dvs-standby-voltage = <850000>;
> > > > 
> > > > Buck2 is not turned off in DSM on i.MX8MP?
> > > 
> > > It is turned off in SUSPEND/SNVS/OFF , not in IDLE/RUN .
> > 
> > Right.  But nxp,dvs-standby-voltage specifies the voltage when PMIC
> > is in STANDBY mode.  My understanding is that the SoC will be in SUSPEND
> > state while PMIC is in STANDBY mode.
> 
> I agree
> 
> > Is it possible that the SoC in
> > IDLE/RUN while PMIC is in STANDBY mode at all?
> 
> No, I don't think so, but there's still the PMIC part:
> 
> https://www.nxp.com/docs/en/data-sheet/PCA9450.pdf
> 
> 7.3.7 STANDBY mode
> "
> PCA9450 transitions to STANDBY mode from RUN mode when
> both PMIC_ON_REQ and PMIC_STBY_REQ are driven high. BUCK1
> and BUCK3 output voltage is set to BUCK1OUT_DVS1 and
> BUCK3OUT_DVS1 and BUCK2 are turned off when DVS_CTRL bit
> in each BUCKx_CTRL register is configured to 1.
> "
> 
> Specifically
> "
> BUCK2 are turned off when DVS_CTRL bit in each
> BUCKx_CTRL register is configured to 1.
> "
> 
> 8.2.19 0x13 BUCK2CTRL
> "
> 4
> DVS_CTRL
> DVS Control configuration
> 0b = BUCK voltage is determined by BUCK2VOUT_DVS0 register regardless of
> PMIC_STBY_REQ
> 1b = DVS control through PMIC_STBY_REQ
> "
> 
> Notice that the reset-default is '0b' , so unless the PMIC is reconfigured,
> the BUCK2 will stay powered on even in STANDBY/SUSPEND.

Hmm, isn't B2_ENMODE controlling on/off of BUCK2?

BUCK2 enable mode
00b = OFF
01b = ON by PMIC_ON_REQ = H
10b = ON by PMIC_ON_REQ = H && PMIC_STBY_REQ = L (default)
11b = Always ON

So unless you reconfigure the field, BUCK2 will be off when PMIC_STBY_REQ
goes high, right?

Shawn