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Message-ID: <54iirnbdmcvbg2zpkajuwqjdb6mxlehpvtnq2hmxd4beuh4ish@mbuttdzzvebv>
Date: Mon, 11 Nov 2024 22:33:51 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
Cc: Vinod Koul <vkoul@...nel.org>, Andi Shyti <andi.shyti@...nel.org>,
Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>,
linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-i2c@...r.kernel.org, linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linaro-mm-sig@...ts.linaro.org, quic_msavaliy@...cinc.com, quic_vtanuku@...cinc.com
Subject: Re: [PATCH v2 RESEND 3/3] i2c: i2c-qcom-geni: Add Block event
interrupt support
On Mon, Nov 11, 2024 at 07:32:44PM +0530, Jyothi Kumar Seerapu wrote:
> The I2C driver gets an interrupt upon transfer completion.
> For multiple messages in a single transfer, N interrupts will be
> received for N messages, leading to significant software interrupt
> latency. To mitigate this latency, utilize Block Event Interrupt (BEI)
Please rewrite this to the tone that the reader doesn't know what Block
Event Interrupt is, or that it exists.
> only when an interrupt is necessary. This means large transfers can be
> split into multiple chunks of 8 messages internally, without expecting
> interrupts for the first 7 message completions, only the last one will
> trigger an interrupt indicating 8 messages completed.
>
> By implementing BEI, multi-message transfers can be divided into
> chunks of 8 messages, improving overall transfer time.
You already wrote this in the paragraph above.
Where is this number 8 coming from btw?
> This optimization reduces transfer time from 168 ms to 48 ms for a
> series of 200 I2C write messages in a single transfer, with a
> clock frequency support of 100 kHz.
>
> BEI optimizations are currently implemented for I2C write transfers only,
> as there is no use case for multiple I2C read messages in a single transfer
> at this time.
>
> Signed-off-by: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
> ---
>
> v1 -> v2:
> - Moved gi2c_gpi_xfer->msg_idx_cnt to separate local variable.
> - Updated goto labels for error scenarios in geni_i2c_gpi function
> - memset tx_multi_xfer to 0.
> - Removed passing current msg index to geni_i2c_gpi.
> - Fixed kernel test robot reported compilation issues.
>
> drivers/i2c/busses/i2c-qcom-geni.c | 203 +++++++++++++++++++++++++----
> 1 file changed, 178 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index 7a22e1f46e60..04a7d926dadc 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -100,6 +100,10 @@ struct geni_i2c_dev {
> struct dma_chan *rx_c;
> bool gpi_mode;
> bool abort_done;
> + bool is_tx_multi_xfer;
> + u32 num_msgs;
> + u32 tx_irq_cnt;
> + struct gpi_i2c_config *gpi_config;
> };
>
> struct geni_i2c_desc {
> @@ -500,6 +504,7 @@ static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> static void i2c_gpi_cb_result(void *cb, const struct dmaengine_result *result)
> {
> struct geni_i2c_dev *gi2c = cb;
> + struct gpi_multi_xfer *tx_multi_xfer;
>
> if (result->result != DMA_TRANS_NOERROR) {
> dev_err(gi2c->se.dev, "DMA txn failed:%d\n", result->result);
> @@ -508,7 +513,21 @@ static void i2c_gpi_cb_result(void *cb, const struct dmaengine_result *result)
> dev_dbg(gi2c->se.dev, "DMA xfer has pending: %d\n", result->residue);
> }
>
> - complete(&gi2c->done);
> + if (gi2c->is_tx_multi_xfer) {
Wouldn't it be cleaner to treat the !is_tx_multi_xfer case as a
multi-xfer of length 1?
> + tx_multi_xfer = &gi2c->gpi_config->multi_xfer;
> +
> + /*
> + * Send Completion for last message or multiple of NUM_MSGS_PER_IRQ.
> + */
> + if ((tx_multi_xfer->irq_msg_cnt == gi2c->num_msgs - 1) ||
> + (!((tx_multi_xfer->irq_msg_cnt + 1) % NUM_MSGS_PER_IRQ))) {
> + tx_multi_xfer->irq_cnt++;
> + complete(&gi2c->done);
Why? You're removing the wait_for_completion_timeout() from
geni_i2c_gpi_xfer() when is_tx_multi_xfer is set.
> + }
> + tx_multi_xfer->irq_msg_cnt++;
> + } else {
> + complete(&gi2c->done);
> + }
> }
>
> static void geni_i2c_gpi_unmap(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> @@ -526,7 +545,42 @@ static void geni_i2c_gpi_unmap(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> }
> }
>
> -static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> +/**
> + * gpi_i2c_multi_desc_unmap() - unmaps the buffers post multi message TX transfers
> + * @dev: pointer to the corresponding dev node
> + * @gi2c: i2c dev handle
> + * @msgs: i2c messages array
> + * @peripheral: pointer to the gpi_i2c_config
> + */
> +static void gpi_i2c_multi_desc_unmap(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[],
> + struct gpi_i2c_config *peripheral)
> +{
> + u32 msg_xfer_cnt, wr_idx = 0;
> + struct gpi_multi_xfer *tx_multi_xfer = &peripheral->multi_xfer;
> +
> + /*
> + * In error case, need to unmap all messages based on the msg_idx_cnt.
> + * Non-error case unmap all the processed messages.
What is the benefit of this optimization, compared to keeping things
simple and just unmap all buffers at the end of geni_i2c_gpi_xfer()?
> + */
> + if (gi2c->err)
> + msg_xfer_cnt = tx_multi_xfer->msg_idx_cnt;
> + else
> + msg_xfer_cnt = tx_multi_xfer->irq_cnt * NUM_MSGS_PER_IRQ;
> +
> + /* Unmap the processed DMA buffers based on the received interrupt count */
> + for (; tx_multi_xfer->unmap_msg_cnt < msg_xfer_cnt; tx_multi_xfer->unmap_msg_cnt++) {
> + if (tx_multi_xfer->unmap_msg_cnt == gi2c->num_msgs)
> + break;
> + wr_idx = tx_multi_xfer->unmap_msg_cnt % QCOM_GPI_MAX_NUM_MSGS;
> + geni_i2c_gpi_unmap(gi2c, &msgs[tx_multi_xfer->unmap_msg_cnt],
> + tx_multi_xfer->dma_buf[wr_idx],
> + tx_multi_xfer->dma_addr[wr_idx],
> + NULL, (dma_addr_t)NULL);
> + tx_multi_xfer->freed_msg_cnt++;
> + }
> +}
> +
> +static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[],
> struct dma_slave_config *config, dma_addr_t *dma_addr_p,
> void **buf, unsigned int op, struct dma_chan *dma_chan)
> {
> @@ -538,26 +592,48 @@ static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> enum dma_transfer_direction dma_dirn;
> struct dma_async_tx_descriptor *desc;
> int ret;
> + struct gpi_multi_xfer *gi2c_gpi_xfer;
> + dma_cookie_t cookie;
> + u32 msg_idx;
>
> peripheral = config->peripheral_config;
> -
> - dma_buf = i2c_get_dma_safe_msg_buf(msg, 1);
> - if (!dma_buf)
> - return -ENOMEM;
> + gi2c_gpi_xfer = &peripheral->multi_xfer;
> + dma_buf = gi2c_gpi_xfer->dma_buf[gi2c_gpi_xfer->buf_idx];
> + addr = gi2c_gpi_xfer->dma_addr[gi2c_gpi_xfer->buf_idx];
> + msg_idx = gi2c_gpi_xfer->msg_idx_cnt;
> +
> + dma_buf = i2c_get_dma_safe_msg_buf(&msgs[msg_idx], 1);
> + if (!dma_buf) {
> + ret = -ENOMEM;
> + goto out;
> + }
>
> if (op == I2C_WRITE)
> map_dirn = DMA_TO_DEVICE;
> else
> map_dirn = DMA_FROM_DEVICE;
>
> - addr = dma_map_single(gi2c->se.dev->parent, dma_buf, msg->len, map_dirn);
> + addr = dma_map_single(gi2c->se.dev->parent, dma_buf,
> + msgs[msg_idx].len, map_dirn);
> if (dma_mapping_error(gi2c->se.dev->parent, addr)) {
> - i2c_put_dma_safe_msg_buf(dma_buf, msg, false);
> - return -ENOMEM;
> + i2c_put_dma_safe_msg_buf(dma_buf, &msgs[msg_idx], false);
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + if (gi2c->is_tx_multi_xfer) {
> + if (((msg_idx + 1) % NUM_MSGS_PER_IRQ))
> + peripheral->flags |= QCOM_GPI_BLOCK_EVENT_IRQ;
> + else
> + peripheral->flags &= ~QCOM_GPI_BLOCK_EVENT_IRQ;
> +
> + /* BEI bit to be cleared for last TRE */
> + if (msg_idx == gi2c->num_msgs - 1)
> + peripheral->flags &= ~QCOM_GPI_BLOCK_EVENT_IRQ;
> }
>
> /* set the length as message for rx txn */
> - peripheral->rx_len = msg->len;
> + peripheral->rx_len = msgs[msg_idx].len;
> peripheral->op = op;
>
> ret = dmaengine_slave_config(dma_chan, config);
> @@ -575,7 +651,8 @@ static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> else
> dma_dirn = DMA_DEV_TO_MEM;
>
> - desc = dmaengine_prep_slave_single(dma_chan, addr, msg->len, dma_dirn, flags);
> + desc = dmaengine_prep_slave_single(dma_chan, addr, msgs[msg_idx].len,
> + dma_dirn, flags);
> if (!desc) {
> dev_err(gi2c->se.dev, "prep_slave_sg failed\n");
> ret = -EIO;
> @@ -585,15 +662,48 @@ static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> desc->callback_result = i2c_gpi_cb_result;
> desc->callback_param = gi2c;
>
> - dmaengine_submit(desc);
> - *buf = dma_buf;
> - *dma_addr_p = addr;
> + if (!((msgs[msg_idx].flags & I2C_M_RD) && op == I2C_WRITE)) {
> + gi2c_gpi_xfer->msg_idx_cnt++;
> + gi2c_gpi_xfer->buf_idx = (msg_idx + 1) % QCOM_GPI_MAX_NUM_MSGS;
> + }
> + cookie = dmaengine_submit(desc);
> + if (dma_submit_error(cookie)) {
> + dev_err(gi2c->se.dev,
> + "%s: dmaengine_submit failed (%d)\n", __func__, cookie);
> + ret = -EINVAL;
> + goto err_config;
> + }
>
> + if (gi2c->is_tx_multi_xfer) {
> + dma_async_issue_pending(gi2c->tx_c);
> + if ((msg_idx == (gi2c->num_msgs - 1)) ||
> + (gi2c_gpi_xfer->msg_idx_cnt >=
> + QCOM_GPI_MAX_NUM_MSGS + gi2c_gpi_xfer->freed_msg_cnt)) {
> + ret = gpi_multi_desc_process(gi2c->se.dev, gi2c_gpi_xfer,
A function call straight into the GPI driver? I'm not entirely familiar
with the details of the dmaengine API, but this doesn't look correct.
> + gi2c->num_msgs, XFER_TIMEOUT,
> + &gi2c->done);
> + if (ret) {
> + dev_err(gi2c->se.dev,
> + "I2C multi write msg transfer timeout: %d\n",
> + ret);
> + gi2c->err = ret;
> + goto err_config;
> + }
> + }
> + } else {
> + /* Non multi descriptor message transfer */
> + *buf = dma_buf;
> + *dma_addr_p = addr;
> + }
> return 0;
>
> err_config:
> - dma_unmap_single(gi2c->se.dev->parent, addr, msg->len, map_dirn);
> - i2c_put_dma_safe_msg_buf(dma_buf, msg, false);
> + dma_unmap_single(gi2c->se.dev->parent, addr,
> + msgs[msg_idx].len, map_dirn);
> + i2c_put_dma_safe_msg_buf(dma_buf, &msgs[msg_idx], false);
> +
> +out:
> + gi2c->err = ret;
> return ret;
> }
>
> @@ -605,6 +715,7 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> unsigned long time_left;
> dma_addr_t tx_addr, rx_addr;
> void *tx_buf = NULL, *rx_buf = NULL;
> + struct gpi_multi_xfer *tx_multi_xfer;
> const struct geni_i2c_clk_fld *itr = gi2c->clk_fld;
>
> config.peripheral_config = &peripheral;
> @@ -618,6 +729,34 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> peripheral.set_config = 1;
> peripheral.multi_msg = false;
>
> + gi2c->gpi_config = &peripheral;
> + gi2c->num_msgs = num;
> + gi2c->is_tx_multi_xfer = false;
> + gi2c->tx_irq_cnt = 0;
> +
> + tx_multi_xfer = &peripheral.multi_xfer;
> + memset(tx_multi_xfer, 0, sizeof(struct gpi_multi_xfer));
> +
> + /*
> + * If number of write messages are four and higher then
Why four?
> + * configure hardware for multi descriptor transfers with BEI.
> + */
> + if (num >= MIN_NUM_OF_MSGS_MULTI_DESC) {
> + gi2c->is_tx_multi_xfer = true;
> + for (i = 0; i < num; i++) {
> + if (msgs[i].flags & I2C_M_RD) {
> + /*
> + * Multi descriptor transfer with BEI
> + * support is enabled for write transfers.
> + * Add BEI optimization support for read
> + * transfers later.
Prefix this comment with "TODO:"
> + */
> + gi2c->is_tx_multi_xfer = false;
> + break;
> + }
> + }
> + }
> +
> for (i = 0; i < num; i++) {
> gi2c->cur = &msgs[i];
> gi2c->err = 0;
> @@ -628,14 +767,16 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> peripheral.stretch = 1;
>
> peripheral.addr = msgs[i].addr;
> + if (i > 0 && (!(msgs[i].flags & I2C_M_RD)))
> + peripheral.multi_msg = false;
>
> - ret = geni_i2c_gpi(gi2c, &msgs[i], &config,
> + ret = geni_i2c_gpi(gi2c, msgs, &config,
> &tx_addr, &tx_buf, I2C_WRITE, gi2c->tx_c);
> if (ret)
> goto err;
>
> if (msgs[i].flags & I2C_M_RD) {
> - ret = geni_i2c_gpi(gi2c, &msgs[i], &config,
> + ret = geni_i2c_gpi(gi2c, msgs, &config,
> &rx_addr, &rx_buf, I2C_READ, gi2c->rx_c);
> if (ret)
> goto err;
> @@ -643,18 +784,26 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> dma_async_issue_pending(gi2c->rx_c);
> }
>
> - dma_async_issue_pending(gi2c->tx_c);
> -
> - time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT);
> - if (!time_left)
> - gi2c->err = -ETIMEDOUT;
> + if (!gi2c->is_tx_multi_xfer) {
> + dma_async_issue_pending(gi2c->tx_c);
> + time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT);
By making this conditional on !is_tx_multi_xfer transfers, what makes
the loop wait for the transfer to complete before you below unmap the
buffers?
> + if (!time_left) {
> + dev_err(gi2c->se.dev, "%s:I2C timeout\n", __func__);
> + gi2c->err = -ETIMEDOUT;
> + }
> + }
>
> if (gi2c->err) {
> ret = gi2c->err;
> goto err;
> }
>
> - geni_i2c_gpi_unmap(gi2c, &msgs[i], tx_buf, tx_addr, rx_buf, rx_addr);
> + if (!gi2c->is_tx_multi_xfer) {
> + geni_i2c_gpi_unmap(gi2c, &msgs[i], tx_buf, tx_addr, rx_buf, rx_addr);
> + } else if (gi2c->tx_irq_cnt != tx_multi_xfer->irq_cnt) {
> + gi2c->tx_irq_cnt = tx_multi_xfer->irq_cnt;
> + gpi_i2c_multi_desc_unmap(gi2c, msgs, &peripheral);
> + }
> }
>
> return num;
> @@ -663,7 +812,11 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> dev_err(gi2c->se.dev, "GPI transfer failed: %d\n", ret);
> dmaengine_terminate_sync(gi2c->rx_c);
> dmaengine_terminate_sync(gi2c->tx_c);
> - geni_i2c_gpi_unmap(gi2c, &msgs[i], tx_buf, tx_addr, rx_buf, rx_addr);
> + if (gi2c->is_tx_multi_xfer)
> + gpi_i2c_multi_desc_unmap(gi2c, msgs, &peripheral);
> + else
> + geni_i2c_gpi_unmap(gi2c, &msgs[i], tx_buf, tx_addr, rx_buf, rx_addr);
> +
As above, it would be nice if multi-xfer was just a special case with a
single buffer; rather than inflating the cyclomatic complexity.
Regards,
Bjorn
> return ret;
> }
>
> --
> 2.17.1
>
>
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