From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Subject: Re: [PATCH 3/3] dmaengine: tegra-adma: Add support for Tegra210 ADMA
Date: Fri, 25 Sep 2015 17:47:44 +0200
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References: <1443193000-457-1-git-send-email-jonathanh@nvidia.com> <56056589.9010704@nvidia.com> <56056A8F.5010103@nvidia.com>
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To: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Cc: Laxman Dewangan <ldewangan-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>, Vinod Koul <vinod.koul-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>, Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Alexandre Courbot <gnurou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>, Ian Campbell <ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>, Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: devicetree@vger.kernel.org

On Friday 25 September 2015 16:38:55 Jon Hunter wrote:
> On 25/09/15 16:17, Jon Hunter wrote:
> > 
> > On 25/09/15 16:03, Arnd Bergmann wrote:
> >> On Friday 25 September 2015 15:56:40 Jon Hunter wrote:
> >>> +       case DMA_MEM_TO_DEV:
> >>> +               burst_size = fls(tdc->config.dst_maxburst);
> >>> +               ch_regs->config = ADMA_CH_CONFIG_SRC_BUF(num_bufs - 1);
> >>> +               ch_regs->ctrl = ADMA_CH_CTRL_XFER_DIR(ADMA_MEM_TO_AHUB) |
> >>> +                               ADMA_CH_CTRL_TX_REQ(tdc->config.slave_id);
> >>> +               ch_regs->src_addr = buf_addr;
> >>> +               break;
> >>> +
> >>> +       case DMA_DEV_TO_MEM:
> >>> +               burst_size = fls(tdc->config.src_maxburst);
> >>> +               ch_regs->config = ADMA_CH_CONFIG_TRG_BUF(num_bufs - 1);
> >>> +               ch_regs->ctrl = ADMA_CH_CTRL_XFER_DIR(ADMA_AHUB_TO_MEM) |
> >>> +                               ADMA_CH_CTRL_RX_REQ(tdc->config.slave_id);
> >>> +               ch_regs->trg_addr = buf_addr;
> >>> +               break;
> >>
> >> Do not use the 'slave_id' field here to identify the slave device, that
> >> concept is broken. Instead, put the slave identification into the
> >> dma specifier in DT and read it out in your xlate function.
> > 
> > Why is it broken?
> > 
> > What happens if I don't know the slave-id? In other words, the slave-id
> > can be dynamically allocated and associated with a given slave.
> 
> I guess thinking about it some more, the driver could assign an id
> itself to a given channel and I could avoid using slave_id here. There
> are 22 channels and 10 tx and 10 rx requests.

This sounds roughly right. So you could pick the ch_regs->ctrl value
when you allocate the tegra_adma_chan structure, and then map it to
the slave in the xlate() function.

> However, I could also
> statically assign a mapping in DT for the clients if that is preferred.

That's not what I was looking for, the DT should contain the information
that the DMA master uses to identify a device, not a setting that it
can freely choose.

	Arnd