linux-kernel - Re: [PATCH v2] dmaengine: axi-dmac: Request IRQ with IRQF

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Message-ID: <CAJYdmeO=k06MJi1L8++BC_zPqeb-BkrT=a7GOOCUE17Tk093NA@mail.gmail.com>
Date:   Fri, 27 Apr 2018 08:15:32 -0700
From:   Moritz Fischer <moritz.fischer.private@...il.com>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dmaengine@...r.kernel.org, dan.j.williams@...el.com
Subject: Re: [PATCH v2] dmaengine: axi-dmac: Request IRQ with IRQF_SHARED

Hi Vinod,

On Fri, Apr 27, 2018 at 12:08 AM, Vinod Koul <vinod.koul@...el.com> wrote:
> On Fri, Apr 27, 2018 at 08:53:39AM +0200, Lars-Peter Clausen wrote:
>> On 04/27/2018 07:11 AM, Vinod Koul wrote:
>> > On Thu, Apr 26, 2018 at 10:40:00AM -0700, Moritz Fischer wrote:
>> >> Request IRQ with IRQF_SHARED flag. This works since the interrupt
>> >> handler already checks if there is an actual IRQ pending and returns
>> >> IRQ_NONE otherwise.
>> >
>> > hmmm what are we trying to fix here? Is your device on a shared line or not?
>>
>> IRQF_SHARED does not mean that the IRQ is on a shared line. It means that
>> the driver can handle it if the IRQ is on a shared line. Since the driver
>> can handle it setting the flag is a good idea since this enables usecases
>> where the line is shared.
>
> Yes that is correct indeed, but what is the motivation for the change.
>
> If you never expect this to be in shared environment why to do this?
> Sorry but "it works" is not a good enough reason for this change, to enable
> usecases where the line is shared is a good reason :)

Remember, this is an FPGA soft core. I happen to have a design [1] where it
is hooked up with multiple of them on one IRQ line, so to make this work,
I need this change.

Thanks,

Moritz

[1] https://www.ettus.com/product/details/USRP-N310