linux-kernel - Re: [PATCH v3 1/3] ARM: dts: da850: add cpu node and operating points to DT

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Date:   Mon, 15 Apr 2019 15:51:13 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
CC:     Kevin Hilman <khilman@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Lechner <david@...hnology.com>,
        Adam Ford <aford173@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v3 1/3] ARM: dts: da850: add cpu node and operating points
 to DT

On 12/04/19 9:01 PM, Bartosz Golaszewski wrote:
> pt., 12 kwi 2019 o 15:53 Sekhar Nori <nsekhar@...com> napisał(a):
>>
>> On 12/04/19 5:41 PM, Bartosz Golaszewski wrote:
>>> pt., 12 kwi 2019 o 13:26 Sekhar Nori <nsekhar@...com> napisał(a):
>>>>
>>>> Hi Bartosz,
>>>>
>>>> On 08/04/19 1:29 PM, Bartosz Golaszewski wrote:
>>>>> From: David Lechner <david@...hnology.com>
>>>>>
>>>>> This adds a cpu node and operating points to the common da850.dtsi file.
>>>>>
>>>>> Additionally, a regulator is added to the LEGO EV3 board along with
>>>>> some board-specific CPU configuration.
>>>>>
>>>>> Regulators need to be hooked up on other boards to get them working.
>>>>>
>>>>> Signed-off-by: David Lechner <david@...hnology.com>
>>>>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>>>
>>>> I remember you mentioning about some problems using OCHI and cpufreq
>>>> together. Are those resolved now? CPU PLL on DA850 can affect other
>>>> peripheral clock frequencies too. So enabling it should really be a
>>>> per-board decision.
>>>>
>>>
>>> The problems are still there. I've never been able to find the
>>> culprit, but it also occurs on TI BSP in the same way (a couple
>>> cpufreq transitions will make the controller unresponsive).
>>
>> Is that on LCDK as well? As I recall cpufreq was never enabled on LCDK
>> in TI BSP.
>>
> 
> Yes, I just verified that the bug occurs on LCDK with patches from this series.
> 
>> If the OHCI problem is present on LCDK, then there is a user visible
>> regression on mainline after this patch. Lets enable cpufreq in LCDK
>> only if all working peripherals keep working afterwards.
>>
> 
> The OHCI driver doesn't register any cpufreq transition notifier
> callbacks. I can't really find anything in the datasheet, but I'm
> wondering if we shouldn't do something similar to what the driver for
> davinci i2c controller does. I'll try a couple things tomorrow.

Even if OHCI issue is fixed, with a fixed regulator like on LCDK, I am
not sure the benefits of just frequency scaling will be justifiable enough.

Fixing the OHCI issue may help in other boards like da850-evm use it
though. So that will be a good thing.

How do you feel about keeping all OPPs disabled by default in da850.dtsi
and enabling only the ones that make sense for a board in <board>.dts?

Empty OPP table is illegal, so this does mean that every board must
enable at least one OPP.

Thanks,
Sekhar