From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 3/3] dmaengine: tegra-adma: Add support for Tegra210 ADMA
Date: Fri, 25 Sep 2015 16:38:55 +0100
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To: Arnd Bergmann <arnd-r2nGTMty4D4@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 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. However, I could also
statically assign a mapping in DT for the clients if that is preferred.

Jon