linux-kernel - Re: [PATCH v16 3/7] soc: mediatek: SVS: introduce MTK SVS engine

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Date:   Thu, 13 May 2021 20:33:14 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Roger Lu <roger.lu@...iatek.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Enric Balletbo Serra <eballetbo@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Nicolas Boichat <drinkcat@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Fan Chen <fan.chen@...iatek.com>,
        HenryC Chen <HenryC.Chen@...iatek.com>,
        YT Lee <yt.lee@...iatek.com>,
        Xiaoqing Liu <Xiaoqing.Liu@...iatek.com>,
        Charles Yang <Charles.Yang@...iatek.com>,
        Angus Lin <Angus.Lin@...iatek.com>,
        Mark Rutland <mark.rutland@....com>,
        Nishanth Menon <nm@...com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v16 3/7] soc: mediatek: SVS: introduce MTK SVS engine

On 5/13/21 8:10 PM, Roger Lu wrote:
> Hi Guenter,
> 
> Sorry for the late reply and thanks for the notice.
> 
> On Wed, 2021-05-05 at 21:51 -0700, Guenter Roeck wrote:
>> On Wed, Apr 28, 2021 at 02:54:36PM +0800, Roger Lu wrote:
>>> The Smart Voltage Scaling(SVS) engine is a piece of hardware
>>> which calculates suitable SVS bank voltages to OPP voltage table.
>>> Then, DVFS driver could apply those SVS bank voltages to PMIC/Buck
>>> when receiving OPP_EVENT_ADJUST_VOLTAGE.
>>>
>>> Signed-off-by: Roger Lu <roger.lu@...iatek.com>
>>> ---
>>>   drivers/soc/mediatek/Kconfig   |   10 +
>>>   drivers/soc/mediatek/Makefile  |    1 +
>>>   drivers/soc/mediatek/mtk-svs.c | 1723
>>> ++++++++++++++++++++++++++++++++
>>>   3 files changed, 1734 insertions(+)
>>>   create mode 100644 drivers/soc/mediatek/mtk-svs.c
>>>
>>
>> [ ... ]
>>
>>> +
>>> +	svsp_irq = irq_of_parse_and_map(svsp->dev->of_node, 0);
>>> +	ret = devm_request_threaded_irq(svsp->dev, svsp_irq, NULL,
>>> svs_isr,
>>> +					svsp->irqflags, svsp->name,
>>> svsp);
>>
>> 0-day reports:
>>
>> drivers/soc/mediatek/mtk-svs.c:1663:7-32: ERROR:
>> 	Threaded IRQ with no primary handler requested without
>> IRQF_ONESHOT
>>
>> I would be a bit concerned about this. There is no primary (hard)
>> interrupt handler, meaning the hard interrupt may be re-enabled after
>> the default hard interrupt handler runs. This might result in endless
>> interrupts.
> 
> Oh, we add IRQF_ONESHOT in "svs_get_svs_mt8183_platform_data()" for
> threaded irq. So, please kindly let us know if we need to set more
> flags or any other potential risks we should be aware. Thanks in
> advance.
> 

After reviewing the code, I think this was actually a false alarm,
at least if svsp->irqflags always includes IRQF_ONESHOT.
The code is kind of unusual, though. Unless I am missing something,
svsp->irqflags is only set in one place and it is always set
to IRQF_TRIGGER_LOW | IRQF_ONESHOT. If there is a remote chance
that the flag is ever different, it would have been better (and less
confusing) to specify IRQF_ONESHOT directly when requesting the
interrupt (because it is always needed, no matter which SOC).
If the flags are always the same, there is no reason for having
the svsp->irqflags variable in the first place.

Thanks,
Guenter