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

On Tue, Aug 23, 2011 at 12:38 PM, Boojin Kim [off-list ref] wrote:

Jassi Brar [mailto:jassisinghbrar at gmail.com]

quoted

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 [off-list ref]
wrote:

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+static struct dma_async_tx_descriptor *pl330_prep_dma_cyclic(
+ ? ? ? ? ? ? ? struct dma_chan *chan, dma_addr_t dma_addr, size_t

len,

quoted

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+ ? ? ? ? ? ? ? size_t period_len, enum dma_data_direction

direction)

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+{
+ ? ? ? 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",

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+ ? ? ? ? ? ? ? ? ? ? ? __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",

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+ ? ? ? ? ? ? ? __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.