linux-kernel - Re: [PATCH v7 2/8] dt-bindings: Introduce interconnect provider bindings

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Date:   Thu, 30 Aug 2018 09:47:04 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Georgi Djakov <georgi.djakov@...aro.org>
Cc:     Rob Herring <robh@...nel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Michael Turquette <mturquette@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        Evan Green <evgreen@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Alexandre Bailon <abailon@...libre.com>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v7 2/8] dt-bindings: Introduce interconnect provider
 bindings

Hi,

On Wed, Aug 29, 2018 at 03:33:29PM +0300, Georgi Djakov wrote:
> On 08/27/2018 06:11 PM, Maxime Ripard wrote:
> > On Fri, Aug 24, 2018 at 10:35:23AM -0500, Rob Herring wrote:
> >> On Fri, Aug 24, 2018 at 9:51 AM Georgi Djakov <georgi.djakov@...aro.org> wrote:
> >>>
> >>> Hi Maxime,
> >>>
> >>> On 08/20/2018 06:32 PM, Maxime Ripard wrote:
> >>>> Hi Georgi,
> >>>>
> >>>> On Tue, Aug 07, 2018 at 05:54:38PM +0300, Georgi Djakov wrote:
> >>>>>> There is also a patch series from Maxime Ripard that's addressing the
> >>>>>> same general area. See "dt-bindings: Add a dma-parent property". We
> >>>>>> don't need multiple ways to address describing the device to memory
> >>>>>> paths, so you all had better work out a common solution.
> >>>>>
> >>>>> Looks like this fits exactly into the interconnect API concept. I see
> >>>>> MBUS as interconnect provider and display/camera as consumers, that
> >>>>> report their bandwidth needs. I am also planning to add support for
> >>>>> priority.
> >>>>
> >>>> Thanks for working on this. After looking at your serie, the one thing
> >>>> I'm a bit uncertain about (and the most important one to us) is how we
> >>>> would be able to tell through which interconnect the DMA are done.
> >>>>
> >>>> This is important to us since our topology is actually quite simple as
> >>>> you've seen, but the RAM is not mapped on that bus and on the CPU's,
> >>>> so we need to apply an offset to each buffer being DMA'd.
> >>>
> >>> Ok, i see - your problem is not about bandwidth scaling but about using
> >>> different memory ranges by the driver to access the same location. So
> >>> this is not really the same and your problem is different. Also the
> >>> interconnect bindings are describing a path and endpoints. However i am
> >>> open to any ideas.
> >>
> >> It may be different things you need, but both are related to the path
> >> between a bus master and memory. We can't have each 'problem'
> >> described in a different way. Well, we could as long as each platform
> >> has different problems, but that's unlikely.
> >>
> >> It could turn out that the only commonality is property naming
> >> convention, but that's still better than 2 independent solutions.
> > 
> > Yeah, I really don't think the two issues are unrelated. Can we maybe
> > have a particular interconnect-names value to mark the interconnect
> > being used to perform DMA?
> 
> We can call one of the paths "dma" and use it to perform DMA for the
> current device. I don't see a problem with this. The name of the path is
> descriptive and makes sense. And by doing we avoid adding more DT
> properties, which would be an other option.

That works for me. If Rob is fine with it too, I'll send an updated
version of my serie based on yours.

Thanks!
Maxime



-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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