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

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.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