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

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

On 29/09/15 09:13, Jon Hunter wrote:
> 
> On 28/09/15 17:36, Stephen Warren wrote:
>> On 09/28/2015 08:57 AM, Jon Hunter wrote:
>>>
>>> On 25/09/15 16:47, Arnd Bergmann wrote:
>>>> 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.
>>>
>>> Actually, what I mentioned about would not work as it is not the DMA
>>> that should assign the requests to the channel.
>>>
>>> I think that I have poorly described the hardware and how it works, so
>>> let me try and explain a bit more.
>>>
>>>  From a hardware perspective it looks like the following ...
>>>
>>> memory <-> adma <-> adma-if <-> xbar <-> clients
>>>
>>> where:
>>> - memory is the system memory
>>> - adma is the dma controller
>>> - adma-if is the dma interface to a crossbar
>>> - xbar is the crossbar
>>> - clients are various audio interfaces, such as i2s, etc
>>>
>>> The adma-if is essentially a mux with 10 tx and 10 rx ports. Any of the
>>> 22 adma channels can be mapped to any of the 10 tx or rx ports. The
>>> request signal used by the adma is determined by which port it is
>>> configured to use. However, what makes this even more configurable is
>>> the xbar is also a mux that can route adma-if ports to the various
>>> clients.
>>>
>>> So potentially, you could use any adma channel and any port to route
>>> audio to any of the clients. However, the adma-if needs to know which
>>> adma channel is mapped to which port
>>
>> It does? I'm pretty sure it didn't in earlier chips; what changed?
> 
> I *believe* that T210 is the first one to have the ADMA controller where
> as previous chips used the APB-DMA controller. Looking at the APB-DMA on
> T124 I can see that there is a fixed REQ_SEL value for each of the APBIF
> (equivalent of the ADMA-IF on T210).

Actually, I think that T210 is the same as the previous chips. Because
of the xbar you could potentially have various different routing
possibilities between the DMA, CIF and client. However, the request
signal between the DMA and CIF is fixed.

Sorry, I think my brain melted while traversing the audio subsystem.

Jon