[PATCH v2 2/2] dmaengine: Add hisilicon k3 DMA engine driver

[zhangfei gao]

On Wed, Aug 21, 2013 at 12:58 PM, Vinod Koul <vinod.koul at intel.com> wrote:
> On Tue, Aug 20, 2013 at 09:36:50PM +0800, zhangfei gao wrote:
>> > and how do you handle when the desc is running on a phy.
>>
>> Currently k3dma is used with uart.
>>
>> drivers/tty/serial/amba-pl011.c
>> pl011_dma_rx_irq: dmaengine_pause -> device_tx_status
>> First pause channel, then get residue.
>> k3_dma_tx_status:
>> a) if desc in issue queue, then it still not started, return total size.
>> b) otherwise get the residue via counting descriptor.
>> pl011 get the residue and recaculate the pending.
> Okay thanks, While looks like for uart this is usage (note this driver doesnt not
> call resume. So for that you dont need resume to be implemented.
>
> Also, the driver will call the residue and then terminate always. So again I dont
> see a point of yours with what your are doing with descriptors.
>
> And since you support PAUSE/RESUME, if someone tries to use this with sound,
> this will break as sound will call pause and then resume. No resubmitting or
> terminating.

In k3v2 platform, k3dma is shared dma, used by peripherals, like uart, ssp.
While audio has special dma, can not used by others, even not use
dmaengine, which expose to system.
PAUSE & RESUME is added ONLY because we found amba-pl011 need when enable dma.

>
>> Have pass the stress test with amba-pl011.
> See the example of amba-pl08x.c, I think Linux W had this in mind when he added
> this and other exapmple of PAUSE and RESUME implemented in drivers
>
> Also, again you PAUSE a channel not a trancation, so it doesnt not really matter
> where the descriptor is. In phy or somehwere else! We shouldnt care

Excuse me for my bad English.
I am really lost and don't know what to do now.
Are you concern:
1. Why need else in case DMA_PAUSE, no need?
2. device_tx_status is not called in audio and directly
dmaengine_pause -> dmaengine_resume?
3. ?

Besides, where I should take example of amba-pl08x.c, pl08x_control,
case DMA_PAUSE & DMA_RESUME or pl08x_dma_tx_status?

Some difference I see is k3dma.c only has one tasklet for all channels,
The tasklet will check pending channel and alloc physical channel.
While the issue_pending does not really alloc physical channel to
support more request then physical channel.
So when suspend we have to consider remove the channel from chan_pending.

When trying use virt-dma, have study drivers/dma/sa11x0-dma.c as good reference.

Sorry for my bad understanding.