Re: [PATCH 3/3] dmaengine: tegra-adma: Add support for Tegra210 ADMA

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 09/25/2015 09:38 AM, 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. However, I could also
> statically assign a mapping in DT for the clients if that is preferred.

The channel IDs should be dynamically assigned at run-time.

DT should provide the slave ID (if there is one) for each client.

The two concepts are completely orthogonal.