[PATCH 7/7] dw_dmac: introduce software emulation of LLP transfers

Andy Shevchenko
2012-09-17T07:39:57Z

Some controllers have the reduced functionality where the LLP multi block
transfers are not supported. This patch introduces a support of such
controllers. In case of memory copy or scatter-gather lists it emulates LLP
transfers via bunch of the regular single block ones.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
drivers/dma/dw_dmac.c | 83 +++++++++++++++++++++++++++++++++++++-------
drivers/dma/dw_dmac_regs.h | 5 +++
2 files changed, 75 insertions(+), 13 deletions(-)

diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
index 00958ad..fa23711 100644
--- a/drivers/dma/dw_dmac.c
+++ b/drivers/dma/dw_dmac.c
@@ -229,10 +229,29 @@ static inline void dwc_chan_disable(struct dw_dma *dw, struct dw_dma_chan *dwc)

/*----------------------------------------------------------------------*/

+/* Perform single block transfer */
+static inline void dwc_do_single_block(struct dw_dma_chan *dwc,
+ struct dw_desc *desc)
+{
+ struct dw_dma *dw = to_dw_dma(dwc->chan.device);
+ u32 ctllo;
+
+ /* Software emulation of LLP mode relies on interrupts to continue
+ * multi block transfer. */
+ ctllo = desc->lli.ctllo | DWC_CTLL_INT_EN;
+
+ channel_writel(dwc, SAR, desc->lli.sar);
+ channel_writel(dwc, DAR, desc->lli.dar);
+ channel_writel(dwc, CTL_LO, ctllo);
+ channel_writel(dwc, CTL_HI, desc->lli.ctlhi);
+ channel_set_bit(dw, CH_EN, dwc->mask);
+}
+
/* Called with dwc->lock held and bh disabled */
static void dwc_dostart(struct dw_dma_chan *dwc, struct dw_desc *first)
{
struct dw_dma *dw = to_dw_dma(dwc->chan.device);
+ unsigned long was_soft_llp;

/* ASSERT: channel is idle */
if (dma_readl(dw, CH_EN) & dwc->mask) {
@@ -244,6 +263,26 @@ static void dwc_dostart(struct dw_dma_chan *dwc, struct dw_desc *first)
return;
}

+ if (dwc->nollp) {
+ was_soft_llp = test_and_set_bit(DW_DMA_IS_SOFT_LLP,
+ &dwc->flags);
+ if (was_soft_llp) {
+ dev_err(chan2dev(&dwc->chan),
+ "BUG: Attempted to start new LLP transfer "
+ "inside ongoing one\n");
+ return;
+ }
+
+ dwc_initialize(dwc);
+
+ dwc->tx_list = &first->tx_list;
+ dwc->tx_node_active = first->tx_list.next;
+
+ dwc_do_single_block(dwc, first);
+
+ return;
+ }
+
dwc_initialize(dwc);

channel_writel(dwc, LLP, first->txd.phys);
@@ -555,8 +594,36 @@ static void dw_dma_tasklet(unsigned long data)
dwc_handle_cyclic(dw, dwc, status_err, status_xfer);
else if (status_err & (1 << i))
dwc_handle_error(dw, dwc);
- else if (status_xfer & (1 << i))
+ else if (status_xfer & (1 << i)) {
+ unsigned long flags;
+
+ spin_lock_irqsave(&dwc->lock, flags);
+ if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
+ if (dwc->tx_node_active != dwc->tx_list) {
+ struct dw_desc *desc =
+ list_entry(dwc->tx_node_active,
+ struct dw_desc,
+ desc_node);
+
+ dma_writel(dw, CLEAR.XFER, dwc->mask);
+
+ /* move pointer to next descriptor */
+ dwc->tx_node_active =
+ dwc->tx_node_active->next;
+
+ dwc_do_single_block(dwc, desc);
+
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ continue;
+ } else {
+ /* we are done here */
+ clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
+ }
+ }
+ spin_unlock_irqrestore(&dwc->lock, flags);
+
dwc_scan_descriptors(dw, dwc);
+ }
}

/*
@@ -647,12 +714,6 @@ dwc_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
unsigned int dst_width;
u32 ctllo;

- if (dwc->nollp) {
- dev_dbg(chan2dev(&dwc->chan),
- "channel doesn't support LLP transfers\n");
- return NULL;
- }
-
dev_vdbg(chan2dev(chan),
"%s: d0x%llx s0x%llx l0x%zx f0x%lx\n", __func__,
(unsigned long long)dest, (unsigned long long)src,
@@ -747,12 +808,6 @@ dwc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
if (unlikely(!dws || !sg_len))
return NULL;

- if (dwc->nollp) {
- dev_dbg(chan2dev(&dwc->chan),
- "channel doesn't support LLP transfers\n");
- return NULL;
- }
-
prev = first = NULL;

switch (direction) {
@@ -972,6 +1027,8 @@ static int dwc_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
} else if (cmd == DMA_TERMINATE_ALL) {
spin_lock_irqsave(&dwc->lock, flags);

+ clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
+
dwc_chan_disable(dw, dwc);

dwc->paused = false;
diff --git a/drivers/dma/dw_dmac_regs.h b/drivers/dma/dw_dmac_regs.h
index b66a716..297ab18 100644
--- a/drivers/dma/dw_dmac_regs.h
+++ b/drivers/dma/dw_dmac_regs.h
@@ -174,6 +174,7 @@ struct dw_dma_regs {

enum dw_dmac_flags {
DW_DMA_IS_CYCLIC = 0,
+ DW_DMA_IS_SOFT_LLP = 1,
};

struct dw_dma_chan {
@@ -184,6 +185,10 @@ struct dw_dma_chan {
bool paused;
bool initialized;

+ /* software emulation of the LLP transfers */
+ struct list_head *tx_list;
+ struct list_head *tx_node_active;
+
spinlock_t lock;

/* these other elements are all protected by lock */
--
1.7.10.4