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    SubjectRe: [PATCH V2 3/7] i2c: sprd: Use global variables to record I2C ack/nack status instead of local variables
    Hi Huangzheng,

    On Mon, Oct 23, 2023 at 04:11:54PM +0800, Huangzheng Lai wrote:
    > We found that when the interrupt bit of the I2C controller is cleared,
    > the ack/nack bit is also cleared at the same time. After clearing the
    > interrupt bit in sprd_i2c_isr(), incorrect ack/nack information will be
    > obtained in sprd_i2c_isr_thread(), resulting in incorrect communication
    > when nack cannot be recognized. To solve this problem, we used a global
    > variable to record ack/nack information before clearing the interrupt
    > bit instead of a local variable.
    >
    > Fixes: 8b9ec0719834 ("i2c: Add Spreadtrum I2C controller driver")
    > Cc: <stable@vger.kernel.org> # v4.14+
    > Signed-off-by: Huangzheng Lai <Huangzheng.Lai@unisoc.com>
    > ---
    > drivers/i2c/busses/i2c-sprd.c | 11 ++++++-----
    > 1 file changed, 6 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/i2c/busses/i2c-sprd.c b/drivers/i2c/busses/i2c-sprd.c
    > index aa602958d4fd..dec627ef408c 100644
    > --- a/drivers/i2c/busses/i2c-sprd.c
    > +++ b/drivers/i2c/busses/i2c-sprd.c
    > @@ -85,6 +85,7 @@ struct sprd_i2c {
    > struct clk *clk;
    > u32 src_clk;
    > u32 bus_freq;
    > + bool ack_flag;

    So that you are telling me that this is not racy because we won't
    receive any irq until we pull the ack down. Am I understanding
    correctly?

    But if this patch is fixing an unstable ack flag, how can I
    believe this won't end up into a race?

    > struct completion complete;
    > struct reset_control *rst;
    > u8 *buf;
    > @@ -119,6 +120,7 @@ static void sprd_i2c_clear_ack(struct sprd_i2c *i2c_dev)
    > {
    > u32 tmp = readl(i2c_dev->base + I2C_STATUS);
    >
    > + i2c_dev->ack_flag = 0;
    > writel(tmp & ~I2C_RX_ACK, i2c_dev->base + I2C_STATUS);
    > }
    >
    > @@ -393,7 +395,6 @@ static irqreturn_t sprd_i2c_isr_thread(int irq, void *dev_id)
    > {
    > struct sprd_i2c *i2c_dev = dev_id;
    > struct i2c_msg *msg = i2c_dev->msg;
    > - bool ack = !(readl(i2c_dev->base + I2C_STATUS) & I2C_RX_ACK);

    Where exactly did you see the ack going to '0', here in the
    thread or in handler?

    > u32 i2c_tran;
    >
    > if (msg->flags & I2C_M_RD)
    > @@ -409,7 +410,7 @@ static irqreturn_t sprd_i2c_isr_thread(int irq, void *dev_id)
    > * For reading data, ack is always true, if i2c_tran is not 0 which
    > * means we still need to contine to read data from slave.
    > */
    > - if (i2c_tran && ack) {
    > + if (i2c_tran && i2c_dev->ack_flag) {
    > sprd_i2c_data_transfer(i2c_dev);
    > return IRQ_HANDLED;
    > }
    > @@ -420,7 +421,7 @@ static irqreturn_t sprd_i2c_isr_thread(int irq, void *dev_id)
    > * If we did not get one ACK from slave when writing data, we should
    > * return -EIO to notify users.
    > */
    > - if (!ack)
    > + if (!i2c_dev->ack_flag)
    > i2c_dev->err = -EIO;
    > else if (msg->flags & I2C_M_RD && i2c_dev->count)
    > sprd_i2c_read_bytes(i2c_dev, i2c_dev->buf, i2c_dev->count);
    > @@ -437,7 +438,6 @@ static irqreturn_t sprd_i2c_isr(int irq, void *dev_id)
    > {
    > struct sprd_i2c *i2c_dev = dev_id;
    > struct i2c_msg *msg = i2c_dev->msg;
    > - bool ack = !(readl(i2c_dev->base + I2C_STATUS) & I2C_RX_ACK);
    > u32 i2c_tran;
    >
    > if (msg->flags & I2C_M_RD)
    > @@ -456,7 +456,8 @@ static irqreturn_t sprd_i2c_isr(int irq, void *dev_id)
    > * means we can read all data in one time, then we can finish this
    > * transmission too.
    > */
    > - if (!i2c_tran || !ack) {
    > + i2c_dev->ack_flag = !(readl(i2c_dev->base + I2C_STATUS) & I2C_RX_ACK);
    > + if (!i2c_tran || !i2c_dev->ack_flag) {
    > sprd_i2c_clear_start(i2c_dev);

    this clear_start() is called both here and in the thread, why?

    Andi

    > sprd_i2c_clear_irq(i2c_dev);
    > }
    > --
    > 2.17.1
    >

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