dw_dmac: introduce software emulation of LLP transfers

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>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

2 files changed, 101 insertions, 4 deletions

diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
index cdc0a1fe2c64..9ca9ca41b83e 100644
--- a/drivers/dma/dw_dmac.c
+++ b/drivers/dma/dw_dmac.c
@@ -232,10 +232,29 @@ 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) {
@@ -247,6 +266,26 @@ 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);
@@ -558,8 +597,36 @@ 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);
+                }
         }
 
         /*
@@ -962,6 +1029,8 @@ 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;
@@ -1204,6 +1273,13 @@ struct dw_cyclic_desc *dw_dma_cyclic_prep(struct dma_chan *chan,
         unsigned long                   flags;
 
         spin_lock_irqsave(&dwc->lock, flags);
+        if (dwc->nollp) {
+                spin_unlock_irqrestore(&dwc->lock, flags);
+                dev_dbg(chan2dev(&dwc->chan),
+                                "channel doesn't support LLP transfers\n");
+                return ERR_PTR(-EINVAL);
+        }
+
         if (!list_empty(&dwc->queue) || !list_empty(&dwc->active_list)) {
                 spin_unlock_irqrestore(&dwc->lock, flags);
                 dev_dbg(chan2dev(&dwc->chan),
@@ -1471,6 +1547,7 @@ static int __devinit dw_probe(struct platform_device *pdev)
         INIT_LIST_HEAD(&dw->dma.channels);
         for (i = 0; i < nr_channels; i++) {
                 struct dw_dma_chan      *dwc = &dw->chan[i];
+                int                     r = nr_channels - i - 1;
 
                 dwc->chan.device = &dw->dma;
                 dma_cookie_init(&dwc->chan);
@@ -1482,7 +1559,7 @@ static int __devinit dw_probe(struct platform_device *pdev)
 
                 /* 7 is highest priority & 0 is lowest. */
                 if (pdata->chan_priority == CHAN_PRIORITY_ASCENDING)
-                        dwc->priority = nr_channels - i - 1;
+                        dwc->priority = r;
                 else
                         dwc->priority = i;
 
@@ -1499,14 +1576,28 @@ static int __devinit dw_probe(struct platform_device *pdev)
                 dwc->dw = dw;
 
                 /* hardware configuration */
-                if (autocfg)
+                if (autocfg) {
+                        unsigned int dwc_params;
+
+                        dwc_params = dma_read_byaddr(regs + r * sizeof(u32),
+                                                     DWC_PARAMS);
+
                         /* Decode maximum block size for given channel. The
                          * stored 4 bit value represents blocks from 0x00 for 3
                          * up to 0x0a for 4095. */
                         dwc->block_size =
                                 (4 << ((max_blk_size >> 4 * i) & 0xf)) - 1;
-                else
+                        dwc->nollp =
+                                (dwc_params >> DWC_PARAMS_MBLK_EN & 0x1) == 0;
+                } else {
                         dwc->block_size = pdata->block_size;
+
+                        /* Check if channel supports multi block transfer */
+                        channel_writel(dwc, LLP, 0xfffffffc);
+                        dwc->nollp =
+                                (channel_readl(dwc, LLP) & 0xfffffffc) == 0;
+                        channel_writel(dwc, LLP, 0);
+                }
         }
 
         /* Clear all interrupts on all channels. */
diff --git a/drivers/dma/dw_dmac_regs.h b/drivers/dma/dw_dmac_regs.h
index 06f03914f022..ff39fa6cd2bc 100644
--- a/drivers/dma/dw_dmac_regs.h
+++ b/drivers/dma/dw_dmac_regs.h
@@ -172,6 +172,7 @@ struct dw_dma_regs {
 
 enum dw_dmac_flags {
         DW_DMA_IS_CYCLIC = 0,
+        DW_DMA_IS_SOFT_LLP = 1,
 };
 
 struct dw_dma_chan {
@@ -182,6 +183,10 @@ 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 */
@@ -195,6 +200,7 @@ struct dw_dma_chan {
 
         /* hardware configuration */
         unsigned int            block_size;
+        bool                    nollp;
 
         /* configuration passed via DMA_SLAVE_CONFIG */
         struct dma_slave_config dma_sconfig;