Re: [PATCH] ARM: i.MX8MP-EVK: increase VDD_ARM to OD voltage

[Lucas Stach <l.stach@pengutronix.de>]

Am Dienstag, dem 07.02.2023 um 10:54 +0100 schrieb Ahmad Fatoum:
> Hello Lucas,
> 
> On 06.02.23 21:59, Lucas Stach wrote:
> > The Linux kernel or whatever is started from Barebox might switch the
> > ARM frequency to OD level, without first reprogramming the PMIC as
> > required. This might lead to system instability. To avoid this,
> > increase VDD_ARM to OD level. When the kernel handles the PMIC properly
> > it will drop the voltage back to ND level when appropriate.
> > 
> > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> >  arch/arm/boards/nxp-imx8mp-evk/lowlevel.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/arm/boards/nxp-imx8mp-evk/lowlevel.c b/arch/arm/boards/nxp-imx8mp-evk/lowlevel.c
> > index 3cb24df1ca3f..d6fc32e65b61 100644
> > --- a/arch/arm/boards/nxp-imx8mp-evk/lowlevel.c
> > +++ b/arch/arm/boards/nxp-imx8mp-evk/lowlevel.c
> > @@ -61,6 +61,12 @@ static struct pmic_config pca9450_cfg[] = {
> >  	{ PCA9450_BUCK1OUT_DVS0, 0x1C },
> >  	{ PCA9450_BUCK1OUT_DVS1, 0x14 },
> >  	{ PCA9450_BUCK1CTRL, 0x59 },
> > +	/*
> > +	 * Increase VDD_ARM to 0.95V to avoid issues in case software after
> > +	 * Barebox switches to the OD ARM frequency without reprogramming the
> > +	 * PMIC first.
> > +	 */
> > +	{ PCA9450_BUCK2OUT_DVS0, 0x1C },
> 
> We use the same PMIC on nxp-imx8mn-evk and newer nxp-imx8mm-evk
> as well. Should we do this there too? Do we need to change something
> for the i.MX8M boards using Rohm PMICs?
> 
Yep, I just checked: both 8MM and 8MN use the same 0.95V ARM voltage
for the OD mode. While I think it's not much a problem in practice as
the kernel does handle the PMIC before trying to switch ARM frequency
in all usual setups, better safe than sorry and put the ARM voltage
into OD on all system.

I'll send separate patches for that.

Regards,
Lucas