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

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Message-ID: <20180428051043.GG6014@localhost>
Date:   Sat, 28 Apr 2018 10:40:43 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Moritz Fischer <moritz.fischer.private@...il.com>,
        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

On Fri, Apr 27, 2018 at 05:18:29PM +0200, Lars-Peter Clausen wrote:
> On 04/27/2018 05:15 PM, Moritz Fischer wrote:
> > 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.
> 
> I think what Vinod is asking for is a change to the commit message saying
> that "this change enables the driver to be used with devices where the
> interrupt line is shared".

Correct, changelog need to reflect why a change was made, down the line
people need to know the reasons, sometimes it might be even you..

-- 
~Vinod