Messages in this thread | | | Subject | Re: [PATCH] ARM: dts: imx6sx-sdb: Remove cpufreq OPP override | From | Leonard Crestez <> | Date | Thu, 4 May 2017 12:42:23 +0300 |
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On Wed, 2017-05-03 at 21:33 +0200, Marek Vasut wrote: > On 05/03/2017 07:58 PM, Leonard Crestez wrote: > > On Wed, 2017-05-03 at 17:59 +0200, Marek Vasut wrote: > > > On 05/03/2017 04:58 PM, Leonard Crestez wrote: > > > > On Wed, 2017-05-03 at 16:26 +0200, Marek Vasut wrote:
> > > > > 2) It actually fixes a problem with the voltage rails such that the DVFS > > > > > works without leaving the system in unstable or dead state. You do > > > > > need the second part of my patch if you drop the OPP hackery, without > > > > > it the power framework cannot correctly configure the core voltages, > > > > > so the patch from Leonard makes things worse.
> > > > No, I think there is a misunderstanding here. The second part of your > > > > patch will cause cpufreq poking at LDOs to indirectly adjust the input > > > > from the PMIC to the minimum required (this is LDO target + > > > > min_dropout_uv). Without it by default VDD_ARM_SOC_IN will remain fixed > > > > as 1375mV from boot.
> > > Who sets / guarantees that default value for ARM and SOC rails ?
> > I think it's from the PMIC hardware itself (but maybe uboot plays with > > it). VDD_ARM_SOC_IN on this board is tied to SW1AB from MMPF0200: > > > > http://www.nxp.com/assets/documents/data/en/data-sheets/MMPF0200.pdf > > > > It seems reasonable to rely on such voltages set externally.
> Isn't it an established rule that Linux should not depend on bootloader > settings ? Or did that change ?
I don't actually know. Is there a hard and fast rule about this, even when it comes to voltages?
In theory it is possible for a bootloader to set a low cpu frequency and low voltage and then have the chip fail when the cpufreq driver attempts to go higher. Setting vin-supply on reg_arm/reg_soc would fix that.
> Well the regulator(s) cannot be correctly configured if the kernel > doesn't have the correct power distribution described in the DT .
It depends on your definition of "correctness". It it certainly possible to get a functional system while only partially describing regulator relationships.
I think there is a further misunderstanding here. I have a problem where imx6sx-sdb rev C boards crash on boot with upstream (but are reported to work fine with rev B). Removing the OPP overrides fixes this specific issue.
I don't object to the second part of your patch, setting correct supply links is a good thing for various reasons. It is just not necessary for fixing the concrete crash mentioned above (and I tested this). It should probably go in a separate patch.
It might seem a pedantic difference but it's good to accurately describe the effect of patches in commit messages. For example it might help somebody looking to backport various fixes.
-- Regards, Leonard
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