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

[Marek Vasut <marex@denx.de>]

On 10/10/23 02:58, Shawn Guo wrote:
> 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?

I think so.

But since the buck2 in DVS behavior is user-configurable, and this can 
be configured by the bootloader, I would say that it is a good idea to 
keep the buck2 DVS value defined in the DT, rather than keep it undefined.

Also note that this board is a development kit, so we just don't know 
what users might do with it.