linux-kernel - Re: [PATCH V2 3/7] i2c: sprd: Use global variables to record I2C ack/nack status instead of local variables

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Message-ID: <CAAA1Nba1meC0YzsXATgBrLJaP-Aep-Ub0-C1m4_RD3LpTV7aiw@mail.gmail.com>
Date:   Mon, 6 Nov 2023 11:01:23 +0800
From:   huangzheng lai <laihuangzheng@...il.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     Huangzheng Lai <Huangzheng.Lai@...soc.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiongpeng Wu <xiongpeng.wu@...soc.com>
Subject: Re: [PATCH V2 3/7] i2c: sprd: Use global variables to record I2C
 ack/nack status instead of local variables

On Mon, Oct 23, 2023 at 7:32 PM Baolin Wang
<baolin.wang@...ux.alibaba.com> wrote:
>
>
>
> On 10/23/2023 4:11 PM, 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
>
> This is a hardware bug?
>

Yes.

> > 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@...r.kernel.org> # v4.14+
> > Signed-off-by: Huangzheng Lai <Huangzheng.Lai@...soc.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;
> >       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);
>
> Before this patch, we will re-read the ack bit form the register, but
> now we just read it in sprd_i2c_isr(). Is it possible that we will miss
> the ack bit?
>

Yes, we will miss the 'ack' bit after clear 'irq' bit.

> >       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);
> >               sprd_i2c_clear_irq(i2c_dev);
> >       }