linux-kernel - Re: [PATCH 2/3] k3dma: add support to reserved minimum channels

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Date:   Fri, 6 Jul 2018 11:39:38 +0530
From:   Vinod <vkoul@...nel.org>
To:     Guodong Xu <guodong.xu@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, dan.j.williams@...el.com,
        liyu65@...ilicon.com, Suzhuangluan <suzhuangluan@...ilicon.com>,
        "xuhongtao (A)" <xuhongtao8@...ilicon.com>,
        zhongkaihua <zhongkaihua@...wei.com>,
        Xuezhiliang <xuezhiliang@...ilicon.com>,
        "xupeng (Q)" <xupeng7@...wei.com>, sunliang10@...wei.com,
        "Fengbaopeng (kevin, Kirin Solution Dept)" 
        <fengbaopeng@...ilicon.com>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] k3dma: add support to reserved minimum channels

On 06-07-18, 11:05, Guodong Xu wrote:
> On Thu, Jun 28, 2018 at 2:02 PM Vinod <vkoul@...nel.org> wrote:
> >
> > On 22-06-18, 11:24, Guodong Xu wrote:
> > > From: Li Yu <liyu65@...ilicon.com>
> > >
> > > On k3 series of SoC, DMA controller reserves some channels for
> > > other on-chip coprocessors. By adding support to dma_min_chan, kernel
> > > will not be able to use these reserved channels.
> > >
> > > One example is on Hi3660 platform, channel 0 is reserved to lpm3.
> > >
> > > Please also refer to Documentation/devicetree/bindings/dma/k3dma.txt
> >
> > and if some other platform has channel X marked for co-processor, maybe
> > a last channel or something in middle, how will this work then?
> >
> Hi， Vinod
> 
> Sorry for delayed response. We checked with Kirin hardware design
> team, so far their design strategy is all Kirin SoC series reserve
> only from minimum side, saying channel 0, then 1, then 2. That impacts
> the current SoC in upstreaming, Kirin960 (Hi3660), and next versions
> in Kirin SoC, Kirin970 and 980, which may hit upstream later.

And what guarantees that they will not change their mind..

> > I am thinking this should be a mask, rather than min.
> >
> 
> So, since this driver k3dma.c is only used by Kirin SoC DMA
> controllers, I would prefer to keep the current design dma_min_chan
> unchanged.
> 
> What do you think?

I would still prefer bitmask to expose the channels you are supposed to
use

-- 
~Vinod