[PATCH v6 04/15] DMA: PL330: Add DMA_CYCLIC capability

[Jassi Brar]

On Tue, Aug 23, 2011 at 12:38 PM, Boojin Kim <boojin.kim at samsung.com> wrote:
> Jassi Brar [mailto:jassisinghbrar at gmail.com]
>> Sent: Tuesday, August 23, 2011 2:42 PM
>> To: Boojin Kim
>> Cc: linux-arm-kernel at lists.infradead.org; linux-samsung-
>> soc at vger.kernel.org; Vinod Koul; Kukjin Kim; Dan Williams; Mark Brown;
>> Grant Likely; Russell King
>> Subject: Re: [PATCH v6 04/15] DMA: PL330: Add DMA_CYCLIC capability
>>
>> On Mon, Aug 22, 2011 at 5:33 PM, Boojin Kim <boojin.kim at samsung.com>
>> wrote:
>> >>
>> >> > +static struct dma_async_tx_descriptor *pl330_prep_dma_cyclic(
>> >> > +               struct dma_chan *chan, dma_addr_t dma_addr, size_t
>> len,
>> >> > +               size_t period_len, enum dma_data_direction
>> direction)
>> >> > +{
>> >> > +       struct dma_pl330_desc *desc;
>> >> > +       struct dma_pl330_chan *pch = to_pchan(chan);
>> >> > +       dma_addr_t dst;
>> >> > +       dma_addr_t src;
>> >> > +
>> >> > +       desc = pl330_get_desc(pch);
>> >> > +       if (!desc) {
>> >> > +               dev_err(pch->dmac->pif.dev, "%s:%d Unable to fetch
>> >> desc\n",
>> >> > +                       __func__, __LINE__);
>> >> > +               return NULL;
>> >> > +       }
>> >> > +
>> >> > +       switch (direction) {
>> >> > +       case DMA_TO_DEVICE:
>> >> > +               desc->rqcfg.src_inc = 1;
>> >> > +               desc->rqcfg.dst_inc = 0;
>> >> > +               src = dma_addr;
>> >> > +               dst = pch->fifo_addr;
>> >> > +               break;
>> >> > +       case DMA_FROM_DEVICE:
>> >> > +               desc->rqcfg.src_inc = 0;
>> >> > +               desc->rqcfg.dst_inc = 1;
>> >> > +               src = pch->fifo_addr;
>> >> > +               dst = dma_addr;
>> >> > +               break;
>> >> > +       default:
>> >> > +               dev_err(pch->dmac->pif.dev, "%s:%d Invalid dma
>> >> direction\n",
>> >> > +               __func__, __LINE__);
>> >> > +               return NULL;
>> >> > +       }
>> >> > +
>> >> > +       desc->rqcfg.brst_size = pch->burst_sz;
>> >> > +       desc->rqcfg.brst_len = 1;
>> >> > +
>> >> > +       if (!pch->cyclic)
>> >> > +               pch->cyclic = CYCLIC_PREP;
>> >> The need for check here seems suspicious.
>> >> Is it really needed? If not, please remove it.
>> > It's required because Cyclic operation is passed from CYCLIC_PREP to
>> > CYCLIC_TRIGGER.
>> I don't see why you need to differentiate between PREP and TRIGGER in
>> cyclic mode. I think, you should simply have 'bool cyclic' instead of
>> enum.
> On cyclic mode, Pl330_tasklet() operation is changed according to the value of
> 'cyclic'.
> In case of CYCLIC_PREP, Pl330_tasklet()operation is same with normal
> operation.
By 'normal' you mean non-cyclic, right?  That doesn't seem correct to do.
Once the desc has been marked cyclic by device_prep_dma_cyclic(), you
shouldn't treat it like a non-cyclic anymore.


> The sequence is following.
> device_prep_dma_cyclic() -> set CYCLIC_PREP -> device_issue_pending() ->
> Pl330_tasklet() with CYCLIC_PREP -> set CYCLIC_TRIGGER -> PL330 IRQ ->
> Pl330_tasklet() with CYCLIC_TRIGGER.
"device_issue_pending() ->Pl330_tasklet() with CYCLIC_PREP" is no different
from "device_issue_pending() ->Pl330_tasklet() with CYCLIC_TRIGGER"
because the list of 'done' xfers would be null yet.