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From: Daniel Mack <>
To: Maarten Brock <>
Subject: Re: [PATCH 4/4] sc16is7xx: Use threaded IRQ
Date: Tue, 19 May 2020 19:37:52 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 5/19/20 6:32 PM, Maarten Brock wrote:
> On 2020-05-18 18:57, Daniel Mack wrote:

>> It's a controller that sits behind another hardware bus itself, so
>> polling is expensive. If the controller would need to check for level
>> IRQs it would need to poll, and then we could as well just poll the UART
>> directly, that's just as good :)
> That depends on the IRQ coming out of the interrupt controller. If that is
> a level interrupt itself, then it is easy to see if all interrupts are
> handled. Further polling zooms in on the devices that require attention.

Yeah, I'm familiar with the concept, but it's not like that here,

>> But again - the UART driver works perfectly fine with edge IRQs as long
>> as the interrupt is not shared.
> If you would require multiple sc16is7xx devices on I2C would you like to
> connect multiple interrupt lines? Or just SCL,SDA and *one* IRQ?
> OTOH for SPI you would require multiple CS already.

Right. Nevertheless, we can allow sharing the IRQ line for level-trigger
capable IRQ controllers, you're right.

>> What many drivers do is try with one setting, and if that fails because
>> the interrupt controller returns an error, they fall back to something
>> else. We could do the same here of course, but it'd be another patch on
>> top, as it's unrelated to the concrete change the patch we're commenting
>> on is bringing in.
>> So what I can add is logic that first tries with IRQF_LOW|IRQF_SHARED,
>> and if that fails, we fall back to IRQF_FALLING and retry. WDYT?
> That sounds like a decent plan.

Okay, I'll add a patch to the series then and resend.

Thanks for your feedback!

      reply	other threads:[~2020-05-19 17:37 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-08 14:37 [PATCH 0/4] sc16is7xx: Add IrDA mode and threaded IRQ Daniel Mack
2020-05-08 14:37 ` [PATCH 1/4] dt-bindings: sc16is7xx: Add flag to activate IrDA mode Daniel Mack
2020-05-18 18:08   ` Rob Herring
2020-05-18 18:41     ` Daniel Mack
2020-05-19 12:01       ` Maarten Brock
2020-05-08 14:37 ` [PATCH 2/4] " Daniel Mack
2020-05-08 14:37 ` [PATCH 3/4] sc16is7xx: Always use falling edge IRQ Daniel Mack
2020-05-09 12:41   ` Maarten Brock
2020-05-08 14:37 ` [PATCH 4/4] sc16is7xx: Use threaded IRQ Daniel Mack
2020-05-09 12:55   ` Maarten Brock
2020-05-17 20:44     ` Daniel Mack
2020-05-18 11:14       ` Maarten Brock
2020-05-18 16:57         ` Daniel Mack
2020-05-19 16:32           ` Maarten Brock
2020-05-19 17:37             ` Daniel Mack [this message]

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