ARM: tegra: Pause DMA when reading transfer count

In order to read an accurate channel transfer count
from the APB DMA engine, the DMA controller must be
paused first.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

1 files changed, 74 insertions, 42 deletions

diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c
index 122e46770d9..998c55ddca4 100644
--- a/arch/arm/mach-tegra/dma.c
+++ b/arch/arm/mach-tegra/dma.c
@@ -135,6 +135,7 @@ struct tegra_dma_channel {
 
 static bool tegra_dma_initialized;
 static DEFINE_MUTEX(tegra_dma_lock);
+static DEFINE_SPINLOCK(enable_lock);
 
 static DECLARE_BITMAP(channel_usage, NV_DMA_MAX_CHANNELS);
 static struct tegra_dma_channel dma_channels[NV_DMA_MAX_CHANNELS];
@@ -200,18 +201,82 @@ static int tegra_dma_cancel(struct tegra_dma_channel *ch)
         return 0;
 }
 
+static unsigned int get_channel_status(struct tegra_dma_channel *ch,
+                        struct tegra_dma_req *req, bool is_stop_dma)
+{
+        void __iomem *addr = IO_ADDRESS(TEGRA_APB_DMA_BASE);
+        unsigned int status;
+
+        if (is_stop_dma) {
+                /*
+                 * STOP the DMA and get the transfer count.
+                 * Getting the transfer count is tricky.
+                 *  - Globally disable DMA on all channels
+                 *  - Read the channel's status register to know the number
+                 *    of pending bytes to be transfered.
+                 *  - Stop the dma channel
+                 *  - Globally re-enable DMA to resume other transfers
+                 */
+                spin_lock(&enable_lock);
+                writel(0, addr + APB_DMA_GEN);
+                udelay(20);
+                status = readl(ch->addr + APB_DMA_CHAN_STA);
+                tegra_dma_stop(ch);
+                writel(GEN_ENABLE, addr + APB_DMA_GEN);
+                spin_unlock(&enable_lock);
+                if (status & STA_ISE_EOC) {
+                        pr_err("Got Dma Int here clearing");
+                        writel(status, ch->addr + APB_DMA_CHAN_STA);
+                }
+                req->status = TEGRA_DMA_REQ_ERROR_ABORTED;
+        } else {
+                status = readl(ch->addr + APB_DMA_CHAN_STA);
+        }
+        return status;
+}
+
+/* should be called with the channel lock held */
+static unsigned int dma_active_count(struct tegra_dma_channel *ch,
+        struct tegra_dma_req *req, unsigned int status)
+{
+        unsigned int to_transfer;
+        unsigned int req_transfer_count;
+        unsigned int bytes_transferred;
+
+        to_transfer = ((status & STA_COUNT_MASK) >> STA_COUNT_SHIFT) + 1;
+        req_transfer_count = ch->req_transfer_count + 1;
+        bytes_transferred = req_transfer_count;
+        if (status & STA_BUSY)
+                bytes_transferred -= to_transfer;
+        /*
+         * In continuous transfer mode, DMA only tracks the count of the
+         * half DMA buffer. So, if the DMA already finished half the DMA
+         * then add the half buffer to the completed count.
+         */
+        if (ch->mode & TEGRA_DMA_MODE_CONTINOUS) {
+                if (req->buffer_status == TEGRA_DMA_REQ_BUF_STATUS_HALF_FULL)
+                        bytes_transferred += req_transfer_count;
+                if (status & STA_ISE_EOC)
+                        bytes_transferred += req_transfer_count;
+        }
+        bytes_transferred *= 4;
+        return bytes_transferred;
+}
+
 int tegra_dma_dequeue_req(struct tegra_dma_channel *ch,
         struct tegra_dma_req *_req)
 {
-        unsigned int csr;
         unsigned int status;
         struct tegra_dma_req *req = NULL;
         int found = 0;
         unsigned long irq_flags;
-        int to_transfer;
-        int req_transfer_count;
+        int stop = 0;
 
         spin_lock_irqsave(&ch->lock, irq_flags);
+
+        if (list_entry(ch->list.next, struct tegra_dma_req, node) == _req)
+                stop = 1;
+
         list_for_each_entry(req, &ch->list, node) {
                 if (req == _req) {
                         list_del(&req->node);
@@ -224,47 +289,12 @@ int tegra_dma_dequeue_req(struct tegra_dma_channel *ch,
                 return 0;
         }
 
-        /* STOP the DMA and get the transfer count.
-         * Getting the transfer count is tricky.
-         *  - Change the source selector to invalid to stop the DMA from
-         *    FIFO to memory.
-         *  - Read the status register to know the number of pending
-         *    bytes to be transferred.
-         *  - Finally stop or program the DMA to the next buffer in the
-         *    list.
-         */
-        csr = readl(ch->addr + APB_DMA_CHAN_CSR);
-        csr &= ~CSR_REQ_SEL_MASK;
-        csr |= CSR_REQ_SEL_INVALID;
-        writel(csr, ch->addr + APB_DMA_CHAN_CSR);
-
-        /* Get the transfer count */
-        status = readl(ch->addr + APB_DMA_CHAN_STA);
-        to_transfer = (status & STA_COUNT_MASK) >> STA_COUNT_SHIFT;
-        req_transfer_count = ch->req_transfer_count;
-        req_transfer_count += 1;
-        to_transfer += 1;
+        if (!stop)
+                goto skip_stop_dma;
 
-        req->bytes_transferred = req_transfer_count;
+        status = get_channel_status(ch, req, true);
+        req->bytes_transferred = dma_active_count(ch, req, status);
 
-        if (status & STA_BUSY)
-                req->bytes_transferred -= to_transfer;
-
-        /* In continuous transfer mode, DMA only tracks the count of the
-         * half DMA buffer. So, if the DMA already finished half the DMA
-         * then add the half buffer to the completed count.
-         *
-         *      FIXME: There can be a race here. What if the req to
-         *      dequue happens at the same time as the DMA just moved to
-         *      the new buffer and SW didn't yet received the interrupt?
-         */
-        if (ch->mode & TEGRA_DMA_MODE_CONTINOUS)
-                if (req->buffer_status == TEGRA_DMA_REQ_BUF_STATUS_HALF_FULL)
-                        req->bytes_transferred += req_transfer_count;
-
-        req->bytes_transferred *= 4;
-
-        tegra_dma_stop(ch);
         if (!list_empty(&ch->list)) {
                 /* if the list is not empty, queue the next request */
                 struct tegra_dma_req *next_req;
@@ -272,6 +302,8 @@ int tegra_dma_dequeue_req(struct tegra_dma_channel *ch,
                         typeof(*next_req), node);
                 tegra_dma_update_hw(ch, next_req);
         }
+
+skip_stop_dma:
         req->status = -TEGRA_DMA_REQ_ERROR_ABORTED;
 
         spin_unlock_irqrestore(&ch->lock, irq_flags);