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

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Date:   Sat, 28 Apr 2018 12:31:11 -0700
From:   Moritz Fischer <mdf@...nel.org>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        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 Sat, Apr 28, 2018 at 10:40:43AM +0530, Vinod Koul wrote:
> 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..

Ok, communication is hard :) Will resubmit with fixed commit message,

Thanks for your feedback,

Moritz