> Quoting [email protected] (2019-06-11 03:41:26)
>> On 2019-06-10 22:51, Stephen Boyd wrote:
>> > Quoting Linus Walleij (2019-06-07 14:08:10)
>> >> On Fri, May 31, 2019 at 8:52 AM Tengfei Fan
>> <[email protected]> >> wrote:
>> >> >> > The gpio interrupt status bit is getting set after the
>> >> > irq is disabled and causing an immediate interrupt after
>> >> > enablling the irq, so clear status bit on irq_unmask.
>> >> >
>> >> > Signed-off-by: Tengfei Fan <[email protected]>
>> >> >> This looks pretty serious, can one of the Qcom maintainers ACK
>> >> this?
>> >> >> Should it be sent to fixes and even stable?
>> >> >> Fixes: tag?
>> >> > > How is the interrupt status bit getting set after the irq is
>> disabled?
>> > It looks like this is a level type interrupt? I thought that after
>> > commit b55326dc969e ("pinctrl: msm: Really mask level interrupts to
>> > prevent latching") this wouldn't be a problem. Am I wrong, or is qcom
>> > just clearing out patches on drivers and this is the last one that
>> > needs
>> > to be upstreamed?
>>
>> Your patch(commit b55326dc969e) can cover our issue, and my patch is
>> no longer needed.
>> Your patch isn't included in our code, so I submitted this patch.
>
> Alright cool. Sounds like this patch can be dropped then and you can
> pick up the patch from upstream into your vendor kernel.
>
Hi Stephen, there is one use case with is not covered by commit
b55326dc969e (
"pinctrl: msm: Really mask level interrupts to prevent latching"). That
happens when
gpio line is toggled between i/o mode and interrupt mode :
1. GPIO is configured as irq line. Peripheral raises interrupt.
2. IRQ handler runs and disables the irq line (through wq work).
3. GPIO is configured for input and and data is received from the
peripheral.
4. Now, when GPIO is re-enabled as irq, we see spurious irq, and there
isn't
any data received on the gpio line, when it is read back after
configuring as input.
This can happen for both edge and level interrupts.
Patch https://lkml.org/lkml/2019/6/17/226 tries to cover this use case.
Can you please
provide your comments?
Thanks
Neeraj
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On Mon, Jun 17, 2019 at 12:35 PM Neeraj Upadhyay <[email protected]> wrote:
> Hi Stephen, there is one use case with is not covered by commit
> b55326dc969e (
>
> "pinctrl: msm: Really mask level interrupts to prevent latching"). That
> happens when
>
> gpio line is toggled between i/o mode and interrupt mode :
>
> 1. GPIO is configured as irq line. Peripheral raises interrupt.
>
> 2. IRQ handler runs and disables the irq line (through wq work).
>
> 3. GPIO is configured for input and and data is received from the
> peripheral.
There is no distinction between using a GPIO line as input
and using it for IRQ. All input GPIOs can be used for IRQs,
if the hardware supports it (has an irqchip).
> 4. Now, when GPIO is re-enabled as irq, we see spurious irq, and there
> isn't
>
> any data received on the gpio line, when it is read back after
> configuring as input.
That's an interesting usecase. Hans Verkuil reworked the
GPIO irq support very elegantly exactly to support this type
of usecase (irq switch on and off dynamically), where he
was even switching the line into output mode between
the IRQ trains. (one-wire transcactions for CEC).
> Patch https://lkml.org/lkml/2019/6/17/226 tries to cover this use case.
> Can you please provide your comments?
What this patch does is clear all pending IRQs at irq
unmask. This is usually safe, unless there may be cases
where you *want* to catch any pending IRQs. I guess
normally you don't so it should be safe?
The corner case is when you start some transaction
or whatever that gets ACKed by an IRQ and you actually
get the IRQ back before you had time to execute the code
enabling the IRQ.
That would be racy and bad code, as you should clearly
enable the IRQ first, then start the transaction. So I think
this patch is safe.
But let's see what Bjorn says.
Yours,
Linus Walleij
Thanks for the review, Linus.
On 6/17/19 5:20 PM, Linus Walleij wrote:
> On Mon, Jun 17, 2019 at 12:35 PM Neeraj Upadhyay <[email protected]> wrote:
>
>> Hi Stephen, there is one use case with is not covered by commit
>> b55326dc969e (
>>
>> "pinctrl: msm: Really mask level interrupts to prevent latching"). That
>> happens when
>>
>> gpio line is toggled between i/o mode and interrupt mode :
>>
>> 1. GPIO is configured as irq line. Peripheral raises interrupt.
>>
>> 2. IRQ handler runs and disables the irq line (through wq work).
>>
>> 3. GPIO is configured for input and and data is received from the
>> peripheral.
> There is no distinction between using a GPIO line as input
> and using it for IRQ. All input GPIOs can be used for IRQs,
> if the hardware supports it (has an irqchip).
Ok
>
>> 4. Now, when GPIO is re-enabled as irq, we see spurious irq, and there
>> isn't
>>
>> any data received on the gpio line, when it is read back after
>> configuring as input.
> That's an interesting usecase. Hans Verkuil reworked the
> GPIO irq support very elegantly exactly to support this type
> of usecase (irq switch on and off dynamically), where he
> was even switching the line into output mode between
> the IRQ trains. (one-wire transcactions for CEC).
>
>> Patch https://lkml.org/lkml/2019/6/17/226 tries to cover this use case.
>> Can you please provide your comments?
> What this patch does is clear all pending IRQs at irq
> unmask. This is usually safe, unless there may be cases
> where you *want* to catch any pending IRQs. I guess
> normally you don't so it should be safe?
We want to clear pending status at irq enable. Afaik, no,
we don't normally track these pending irqs. So, should be
fine here.
>
> The corner case is when you start some transaction
> or whatever that gets ACKed by an IRQ and you actually
> get the IRQ back before you had time to execute the code
> enabling the IRQ.
>
> That would be racy and bad code, as you should clearly
> enable the IRQ first, then start the transaction. So I think
> this patch is safe.
>
> But let's see what Bjorn says.
>
> Yours,
> Linus Walleij
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member of the Code Aurora Forum, hosted by The Linux Foundation