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Subject[PATCH V1] ARM: tegra: Pause DMA when reading transfer count
Date
From: Laxman Dewangan <ldewangan@nvidia.com>

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>

---
arch/arm/mach-tegra/dma.c | 116 ++++++++++++++++++++++++++++----------------
1 files changed, 74 insertions(+), 42 deletions(-)
diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c
index c0cf967..c3529cf 100644
--- a/arch/arm/mach-tegra/dma.c
+++ b/arch/arm/mach-tegra/dma.c
@@ -133,6 +133,7 @@ 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];
@@ -198,18 +199,82 @@ 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);
@@ -222,47 +287,12 @@ 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;
@@ -270,6 +300,8 @@ 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);
--
1.7.1.1


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