linux-kernel - Re: [PATCH V1 05/15] spmi: pmic-arb: cleanup unrequested irqs

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Date:   Wed, 14 Jun 2017 20:34:46 +0530
From:   kgunda@...eaurora.org
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Abhijeet Dharmapurikar <adharmap@...eaurora.org>,
        Subbaraman Narayanamurthy <subbaram@...eaurora.org>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        David Collins <collinsd@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        adharmap@...cinc.com, aghayal@....qualcomm.com,
        linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH V1 05/15] spmi: pmic-arb: cleanup unrequested irqs

On 2017-06-13 07:41, Stephen Boyd wrote:
> On 06/06, kgunda@...eaurora.org wrote:
>> On 2017-05-31 07:27, Stephen Boyd wrote:
>> >On 05/30, Kiran Gunda wrote:
>> >>From: Abhijeet Dharmapurikar <adharmap@...eaurora.org>
>> >>
>> >>We see a unmapped irqs trigger right around bootup. This could
>> >>likely be because the bootloader exited leaving the interrupts
>> >>in an unknown or unhandled state.  Ack and mask the interrupt
>> >>if one is found. A request_irq later will unmask it and also
>> >>setup proper mapping structures.
>> >
>> >Do we have systems where this is causing an interrupt storm due
>> >to a level high interrupt or something? Just plain acking and
>> >masking irqs at boot if we don't have an irq descriptor created
>> >yet doesn't sound like a good idea, because we'll lose all
>> >interrupts that happen before this driver probes?
>> >
>> Yes. There were instances of an interrupt storm without this patch.
>> There is an RT_STATUS register in the  peripheral address space which
>> maintains the real time state and can be read by the client driver
>> before it registers for the irq. Few client drivers such as charger
>> already doing this.
> 
> So you're saying that drivers need to read RT_STATUS to know if
> they have a pending interrupt before requesting it? That sounds
> bogus.
In  many cases a PMIC module driver does need to know the initial state 
of
the hardware during driver initialization and the RT_STATUS register 
indicates
this (irrespective of the IRQ_EN status).  The  reset value of IRQ_EN = 
0 and if
an event occurs before we request an IRQ, there is no way to know the 
initial state
even after we request this irq as there will be no pending interrupt 
because the
HW default value of IRQ_EN = 0. This can be known only through reading 
the RT_STATUS.

I understand your concern of clearing the IRQ before we request it does 
not seem
a clean way, do you have any other recommendation of this could be 
handled ?