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SubjectRe: [PATCH 09/12] i2c: qup: fix buffer overflow for multiple msg of maximum xfer len
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Hey Abhishek,


On 2/3/2018 12:58 AM, Abhishek Sahu wrote:
> The BAM mode requires buffer for start tag data and tx, rx SG
> list. Currently, this is being taken for maximum transfer length
> (65K). But an I2C transfer can have multiple messages and each
> message can be of this maximum length so the buffer overflow will
> happen in this case. Since increasing buffer length won’t be
> feasible since an I2C transfer can contain any number of messages
> so this patch does following changes to make i2c transfers working
> for multiple messages case.
>
> 1. Calculate the required buffers for 2 maximum length messages
> (65K * 2).
> 2. Split the descriptor formation and descriptor scheduling.
> The idea is to fit as many messages in one DMA transfers for 65K
> threshold value (max_xfer_sg_len). Whenever the sg_cnt is
> crossing this, then schedule the BAM transfer and subsequent
> transfer will again start from zero.
>
> Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
> ---
> drivers/i2c/busses/i2c-qup.c | 199 +++++++++++++++++++++++++------------------
> 1 file changed, 118 insertions(+), 81 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> index 6df65ea..ba717bb 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -155,6 +155,7 @@ struct qup_i2c_bam {
> struct qup_i2c_tag tag;
> struct dma_chan *dma;
> struct scatterlist *sg;
> + unsigned int sg_cnt;
> };
>
> struct qup_i2c_dev {
> @@ -195,6 +196,8 @@ struct qup_i2c_dev {
> bool use_dma;
> /* The threshold length above which DMA will be used */
> unsigned int dma_threshold;
> + unsigned int max_xfer_sg_len;
> + unsigned int tag_buf_pos;
> struct dma_pool *dpool;
> struct qup_i2c_tag start_tag;
> struct qup_i2c_bam brx;
> @@ -699,86 +702,86 @@ static int qup_i2c_req_dma(struct qup_i2c_dev *qup)
> return 0;
> }
>
> -static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
> - int num)
> +static int qup_i2c_bam_make_desc(struct qup_i2c_dev *qup, struct i2c_msg *msg)
> +{
> + int ret = 0, limit = QUP_READ_LIMIT;
> + u32 len = 0, blocks, rem;
> + u32 i = 0, tlen, tx_len = 0;
> + u8 *tags;
> +
> + qup_i2c_set_blk_data(qup, msg);
> +
> + blocks = qup->blk.count;
> + rem = msg->len - (blocks - 1) * limit;
> +
> + if (msg->flags & I2C_M_RD) {
> + while (qup->blk.pos < blocks) {
> + tlen = (i == (blocks - 1)) ? rem : limit;
> + tags = &qup->start_tag.start[qup->tag_buf_pos + len];
> + len += qup_i2c_set_tags(tags, qup, msg);
> + qup->blk.data_len -= tlen;
> +
> + /* scratch buf to read the start and len tags */
> + ret = qup_sg_set_buf(&qup->brx.sg[qup->brx.sg_cnt++],
> + &qup->brx.tag.start[0],
> + 2, qup, DMA_FROM_DEVICE);
> +
> + if (ret)
> + return ret;
> +
> + ret = qup_sg_set_buf(&qup->brx.sg[qup->brx.sg_cnt++],
> + &msg->buf[limit * i],
> + tlen, qup,
> + DMA_FROM_DEVICE);
> + if (ret)
> + return ret;
> +
> + i++;
> + qup->blk.pos = i;
> + }
> + ret = qup_sg_set_buf(&qup->btx.sg[qup->btx.sg_cnt++],
> + &qup->start_tag.start[qup->tag_buf_pos],
> + len, qup, DMA_TO_DEVICE);
> + if (ret)
> + return ret;
> +
> + qup->tag_buf_pos += len;
> + } else {
> + while (qup->blk.pos < blocks) {
> + tlen = (i == (blocks - 1)) ? rem : limit;
> + tags = &qup->start_tag.start[qup->tag_buf_pos + tx_len];
> + len = qup_i2c_set_tags(tags, qup, msg);
> + qup->blk.data_len -= tlen;
> +
> + ret = qup_sg_set_buf(&qup->btx.sg[qup->btx.sg_cnt++],
> + tags, len,
> + qup, DMA_TO_DEVICE);
> + if (ret)
> + return ret;
> +
> + tx_len += len;
> + ret = qup_sg_set_buf(&qup->btx.sg[qup->btx.sg_cnt++],
> + &msg->buf[limit * i],
> + tlen, qup, DMA_TO_DEVICE);
> + if (ret)
> + return ret;
> + i++;
> + qup->blk.pos = i;
> + }
> +
> + qup->tag_buf_pos += tx_len;
> + }
> +
> + return 0;
> +}
> +
> +static int qup_i2c_bam_schedule_desc(struct qup_i2c_dev *qup)
> {
> struct dma_async_tx_descriptor *txd, *rxd = NULL;
> - int ret = 0, idx = 0, limit = QUP_READ_LIMIT;
> + int ret = 0;
> dma_cookie_t cookie_rx, cookie_tx;
> - u32 len, blocks, rem;
> - u32 i, tlen, tx_len, tx_buf = 0, rx_buf = 0, off = 0;
> - u8 *tags;
> -
> - while (idx < num) {
> - tx_len = 0, len = 0, i = 0;
> -
> - qup->is_last = (idx == (num - 1));
> -
> - qup_i2c_set_blk_data(qup, msg);
> -
> - blocks = qup->blk.count;
> - rem = msg->len - (blocks - 1) * limit;
> -
> - if (msg->flags & I2C_M_RD) {
> - while (qup->blk.pos < blocks) {
> - tlen = (i == (blocks - 1)) ? rem : limit;
> - tags = &qup->start_tag.start[off + len];
> - len += qup_i2c_set_tags(tags, qup, msg);
> - qup->blk.data_len -= tlen;
> -
> - /* scratch buf to read the start and len tags */
> - ret = qup_sg_set_buf(&qup->brx.sg[rx_buf++],
> - &qup->brx.tag.start[0],
> - 2, qup, DMA_FROM_DEVICE);
> -
> - if (ret)
> - return ret;
> -
> - ret = qup_sg_set_buf(&qup->brx.sg[rx_buf++],
> - &msg->buf[limit * i],
> - tlen, qup,
> - DMA_FROM_DEVICE);
> - if (ret)
> - return ret;
> -
> - i++;
> - qup->blk.pos = i;
> - }
> - ret = qup_sg_set_buf(&qup->btx.sg[tx_buf++],
> - &qup->start_tag.start[off],
> - len, qup, DMA_TO_DEVICE);
> - if (ret)
> - return ret;
> -
> - off += len;
> - } else {
> - while (qup->blk.pos < blocks) {
> - tlen = (i == (blocks - 1)) ? rem : limit;
> - tags = &qup->start_tag.start[off + tx_len];
> - len = qup_i2c_set_tags(tags, qup, msg);
> - qup->blk.data_len -= tlen;
> -
> - ret = qup_sg_set_buf(&qup->btx.sg[tx_buf++],
> - tags, len,
> - qup, DMA_TO_DEVICE);
> - if (ret)
> - return ret;
> -
> - tx_len += len;
> - ret = qup_sg_set_buf(&qup->btx.sg[tx_buf++],
> - &msg->buf[limit * i],
> - tlen, qup, DMA_TO_DEVICE);
> - if (ret)
> - return ret;
> - i++;
> - qup->blk.pos = i;
> - }
> - off += tx_len;
> -
> - }
> - idx++;
> - msg++;
> - }
> + u32 len = 0;
> + u32 tx_buf = qup->btx.sg_cnt, rx_buf = qup->brx.sg_cnt;
>
> /* schedule the EOT and FLUSH I2C tags */
> len = 1;
> @@ -878,11 +881,19 @@ static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
> return ret;
> }
>
> +static void qup_i2c_bam_clear_tag_buffers(struct qup_i2c_dev *qup)
> +{
> + qup->btx.sg_cnt = 0;
> + qup->brx.sg_cnt = 0;
> + qup->tag_buf_pos = 0;
> +}
> +
> static int qup_i2c_bam_xfer(struct i2c_adapter *adap, struct i2c_msg *msg,
> int num)
> {
> struct qup_i2c_dev *qup = i2c_get_adapdata(adap);
> int ret = 0;
> + int idx = 0;
>
> enable_irq(qup->irq);
> ret = qup_i2c_req_dma(qup);
> @@ -905,9 +916,34 @@ static int qup_i2c_bam_xfer(struct i2c_adapter *adap, struct i2c_msg *msg,
> goto out;
>
> writel(qup->clk_ctl, qup->base + QUP_I2C_CLK_CTL);
> + qup_i2c_bam_clear_tag_buffers(qup);
> +
> + for (idx = 0; idx < num; idx++) {
> + qup->msg = msg + idx;
> + qup->is_last = idx == (num - 1);
> +
> + ret = qup_i2c_bam_make_desc(qup, qup->msg);
> + if (ret)
> + break;
> +
> + /*
> + * Make DMA descriptor and schedule the BAM transfer if its
> + * already crossed the maximum length. Since the memory for all
> + * tags buffers have been taken for 2 maximum possible
> + * transfers length so it will never cross the buffer actual
> + * length.
> + */
> + if (qup->btx.sg_cnt > qup->max_xfer_sg_len ||
> + qup->brx.sg_cnt > qup->max_xfer_sg_len ||
> + qup->is_last) {
> + ret = qup_i2c_bam_schedule_desc(qup);
> + if (ret)
> + break;
> +
> + qup_i2c_bam_clear_tag_buffers(qup);
> + }
> + }
>
> - qup->msg = msg;
> - ret = qup_i2c_bam_do_xfer(qup, qup->msg, num);
> out:
> disable_irq(qup->irq);
>
> @@ -1459,7 +1495,8 @@ static int qup_i2c_probe(struct platform_device *pdev)
> else if (ret != 0)
> goto nodma;
>
> - blocks = (MX_BLOCKS << 1) + 1;
> + qup->max_xfer_sg_len = (MX_BLOCKS << 1);
> + blocks = 2 * qup->max_xfer_sg_len + 1;
> qup->btx.sg = devm_kzalloc(&pdev->dev,
> sizeof(*qup->btx.sg) * blocks,
> GFP_KERNEL);
> @@ -1603,7 +1640,7 @@ static int qup_i2c_probe(struct platform_device *pdev)
> one_bit_t = (USEC_PER_SEC / clk_freq) + 1;
> qup->one_byte_t = one_bit_t * 9;
> qup->xfer_timeout = TOUT_MIN * HZ +
> - usecs_to_jiffies(MX_TX_RX_LEN * qup->one_byte_t);
> + usecs_to_jiffies(2 * MX_TX_RX_LEN * qup->one_byte_t);

Maybe it would make sense to add a comment here explaining why the magic
number 2 has been added.
>
> dev_dbg(qup->dev, "IN:block:%d, fifo:%d, OUT:block:%d, fifo:%d\n",
> qup->in_blk_sz, qup->in_fifo_sz,
>

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