GSI hardware generates an interrupt for each transfer completion.
For multiple messages within a single transfer, this results in
N interrupts for N messages, leading to significant software
interrupt latency.
To mitigate this latency, utilize Block Event Interrupt (BEI) mechanism.
Enabling BEI instructs the GSI hardware to prevent interrupt generation
and BEI is disabled when an interrupt is necessary.
When using BEI, consider splitting a single multi-message transfer into
chunks of 8 internally. Interrupts are not expected for the first 7 message
completions, only the last message triggers an interrupt,indicating
the completion of 8 messages.
This BEI mechanism enhances overall transfer efficiency.
Signed-off-by: Jyothi Kumar Seerapu <quic_jseerapu@xxxxxxxxxxx>
---
v2-> v3:
- Renamed gpi_multi_desc_process to gpi_multi_xfer_timeout_handler
- MIN_NUM_OF_MSGS_MULTI_DESC changed from 4 to 2
- Added documentation for newly added changes in "qcom-gpi-dma.h" file
- Updated commit description.
v1 -> v2:
- Changed dma_addr type from array of pointers to array.
- To support BEI functionality with the TRE size of 64 defined in GPI driver,
updated QCOM_GPI_MAX_NUM_MSGS to 16 and NUM_MSGS_PER_IRQ to 4.
drivers/dma/qcom/gpi.c | 48 ++++++++++++++++++++
include/linux/dma/qcom-gpi-dma.h | 76 ++++++++++++++++++++++++++++++++
2 files changed, 124 insertions(+)
diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
index 52a7c8f2498f..5442b65b1638 100644
--- a/drivers/dma/qcom/gpi.c
+++ b/drivers/dma/qcom/gpi.c
@@ -1693,6 +1693,9 @@ static int gpi_create_i2c_tre(struct gchan *chan, struct gpi_desc *desc,
tre->dword[3] = u32_encode_bits(TRE_TYPE_DMA, TRE_FLAGS_TYPE);
tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IEOT);
+
+ if (i2c->flags & QCOM_GPI_BLOCK_EVENT_IRQ)
+ tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_BEI);
}
for (i = 0; i < tre_idx; i++)
@@ -2098,6 +2101,51 @@ static int gpi_find_avail_gpii(struct gpi_dev *gpi_dev, u32 seid)
return -EIO;
}
+/**
+ * gpi_multi_xfer_timeout_handler() - Handle multi message transfer timeout
+ * @dev: pointer to the corresponding dev node
+ * @multi_xfer: pointer to the gpi_multi_xfer
+ * @num_xfers: total number of transfers
+ * @transfer_timeout_msecs: transfer timeout value
+ * @transfer_comp: completion object of the transfer
+ *
+ * This function is used to wait for the processed transfers based on
+ * the interrupts generated upon transfer completion.
+ * Return: On success returns 0, otherwise return error code (-ETIMEDOUT)
+ */
+int gpi_multi_xfer_timeout_handler(struct device *dev, struct gpi_multi_xfer *multi_xfer,
+ u32 num_xfers, u32 transfer_timeout_msecs,
+ struct completion *transfer_comp)
+{
+ int i;
+ u32 max_irq_cnt, time_left;
+
+ max_irq_cnt = num_xfers / NUM_MSGS_PER_IRQ;
+ if (num_xfers % NUM_MSGS_PER_IRQ)
+ max_irq_cnt++;
+
+ /*
+ * Wait for the interrupts of the processed transfers in multiple
+ * of 8 and for the last transfer. If the hardware is fast and
+ * already processed all the transfers then no need to wait.
+ */
+ for (i = 0; i < max_irq_cnt; i++) {
+ reinit_completion(transfer_comp);
+ if (max_irq_cnt != multi_xfer->irq_cnt) {
+ time_left = wait_for_completion_timeout(transfer_comp,
+ transfer_timeout_msecs);
+ if (!time_left) {
+ dev_err(dev, "%s: Transfer timeout\n", __func__);
+ return -ETIMEDOUT;
+ }
+ }
+ if (num_xfers > multi_xfer->msg_idx_cnt)
+ return 0;
+ }
+ return 0;
+}
+EXPORT_SYMBOL_GPL(gpi_multi_xfer_timeout_handler);
+
/* gpi_of_dma_xlate: open client requested channel */
static struct dma_chan *gpi_of_dma_xlate(struct of_phandle_args *args,
struct of_dma *of_dma)
diff --git a/include/linux/dma/qcom-gpi-dma.h b/include/linux/dma/qcom-gpi-dma.h
index 6680dd1a43c6..f001a8ac1887 100644
--- a/include/linux/dma/qcom-gpi-dma.h
+++ b/include/linux/dma/qcom-gpi-dma.h
@@ -15,6 +15,38 @@ enum spi_transfer_cmd {
SPI_DUPLEX,
};
+/**
+ * define QCOM_GPI_BLOCK_EVENT_IRQ - Block event interrupt support
+ *
+ * This is used to enable/disable the Block event interrupt mechanism.
+ */
+#define QCOM_GPI_BLOCK_EVENT_IRQ BIT(0)
+
+/**
+ * define QCOM_GPI_MAX_NUM_MSGS - maximum number of messages support
+ *
+ * This indicates maximum number of messages can allocate and
+ * submit to hardware. To handle more messages beyond this,
+ * need to unmap the processed messages.
+ */
+#define QCOM_GPI_MAX_NUM_MSGS 16
+
+/**
+ * define NUM_MSGS_PER_IRQ - interrupt per messages completion
+ *
+ * This indicates that trigger an interrupt, after the completion of 8 messages.
+ */
+#define NUM_MSGS_PER_IRQ 8
+
+/**
+ * define MIN_NUM_OF_MSGS_MULTI_DESC - \
+ * minimum number of messages to support Block evenet interrupt
+ *
+ * This indicates minimum number of messages in a trenafer required to
+ * process it using block event interrupt mechanism.
+ */
+#define MIN_NUM_OF_MSGS_MULTI_DESC 2
+
/**
* struct gpi_spi_config - spi config for peripheral
*
@@ -51,6 +83,29 @@ enum i2c_op {
I2C_READ,
};
