linux-kernel - Re: Tearing down DMA transfer setup after DMA client has finished

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Date:   Fri, 9 Dec 2016 23:23:49 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Måns Rullgård <mans@...sr.com>
Cc:     Sebastian Frias <sf84@...oste.net>, Mason <slash.tmp@...e.fr>,
        Russell King <linux@....linux.org.uk>,
        dmaengine@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Dan Williams <dan.j.williams@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Jon Mason <jdmason@...zu.us>, Mark Brown <broonie@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lee Jones <lee.jones@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Arnd Bergmann <arnd@...db.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>
Subject: Re: Tearing down DMA transfer setup after DMA client has finished

On Fri, Dec 09, 2016 at 05:28:01PM +0000, Måns Rullgård wrote:
> Vinod Koul <vinod.koul@...el.com> writes:
> 
> > On Fri, Dec 09, 2016 at 11:25:57AM +0100, Sebastian Frias wrote:
> >> 
> >> What concrete solution do you propose?
> >
> > I have already proposed two solutions.
> >
> > A) Request a channel only when you need it. Obviously we can't do virtual
> > channels with this (though we should still use virt-channels framework).
> > The sbox setup and teardown can be done as part of channel request and
> > freeup. PL08x already does this.
> >
> > Downside is that we can only have as many consumers at a time as channels.
> >
> > I have not heard any technical reason for not doing this apart from drivers
> > grab the channel at probe, which is incorrect and needs to be fixed
> > irrespective of the problem at hand.
> >
> > This is my preferred option.
> 
> Sorry, but this is not acceptable.

without outlining why..

> 
> > B) Create a custom driver specific API. This API for example:
> > 	sbox_setup(bool enable, ...)
> > can be called by client to explicitly setup and clear up the sbox setting.
> >
> > This way we can have transactions muxed.
> >
> > I have not heard any arguments on why we shouldn't do this except Russell's
> > comment that A) solves this.
> 
> Driver-specific interfaces are not the solution.  That way lies chaos
> and madness.

Yes fair enough. So would API change which 99% world doesnt need.

> This would all be so much easier if you all would just shut up for a
> moment and let me fix it properly.

Oh please go away, noone is asking you to reply!

-- 
~Vinod