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References: <20201222194850.2274527-1-kph@platinasystems.com> <20210108080521.dzm2gczd3d2ygb5y@pengutronix.de>
In-Reply-To: <20210108080521.dzm2gczd3d2ygb5y@pengutronix.de>
From:   Kevin Herbert <kph@platinasystems.com>
Date:   Thu, 14 Jan 2021 17:27:11 -0800
Message-ID: <CABP=6zY0xV3dLE5t7qad6TauQsaLmQtYi73BS9XBHwZ2FrgM8g@mail.gmail.com>
Subject: Re: [PATCH] i2c-imx.c: Synthesize end of transaction events without
 idle interrupts
To:     Oleksij Rempel <o.rempel@pengutronix.de>
Cc:     Biwen Li <biwen.li@nxp.com>, Leo Li <leoyang.li@nxp.com>,
        linux@rempel-privat.de, kernel@pengutronix.de,
        Wolfram Sang <wsa@the-dreams.de>, shawnguo@kernel.org,
        s.hauer@pengutronix.de, festevam@gmail.com,
        Aisheng Dong <aisheng.dong@nxp.com>,
        Clark Wang <xiaoning.wang@nxp.com>, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jiafei Pan <jiafei.pan@nxp.com>,
        Xiaobo Xie <xiaobo.xie@nxp.com>,
        linux-arm-kernel@lists.infradead.org,
        Biwen Li <biwen.li@oss.nxp.com>
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The loop sends either one or two events to the slave driver. If the
state is I2C_SLAVE_READ_REQUESTED, we synthesize the
I2C_SLAVE_READ_PROCESSED event, and then our state becomes
I2C_SLAVE_READ_PROCESSED. In all other states, we transition to
I2C_SLAVE_STOP and exit the loop.

It is not a busy loop at all. It is calling the callback handler (that
already expects to be in IRQ context) one or two times, and then it
exits the loop.

Kevin


On Fri, Jan 8, 2021 at 12:05 AM Oleksij Rempel <o.rempel@pengutronix.de> wrote:
>
> Hi Kevin Paul,
>
> On Tue, Dec 22, 2020 at 11:48:50AM -0800, Kevin Paul Herbert wrote:
> > Only the Layerscape SoCs have interrupts on bus idle, which facilitate
> > sending events which complete slave bus transactions.
> >
> > Add support for synthesizing missing events. If we see a master request,
> > or a newly addressed slave request, if the last event sent to the backend
> > was I2C_SLAVE_READ_REQUESTED, send the backend a I2C_SLAVE_READ_PROCESSED
> > followed by I2C_SLAVE_STOP. For all other events, send an I2C_SLAVE_STOP.
> >
> > Signed-off-by: Kevin Paul Herbert <kph@platinasystems.com>
> > ---
> >  drivers/i2c/busses/i2c-imx.c | 59 +++++++++++++++++++++++++++++++-----
> >  1 file changed, 52 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> > index b444fbf1a262..b3e2a6a7fc19 100644
> > --- a/drivers/i2c/busses/i2c-imx.c
> > +++ b/drivers/i2c/busses/i2c-imx.c
> > @@ -209,6 +209,7 @@ struct imx_i2c_struct {
> >
> >       struct imx_i2c_dma      *dma;
> >       struct i2c_client       *slave;
> > +     enum i2c_slave_event last_slave_event;
> >  };
> >
> >  static const struct imx_i2c_hwdata imx1_i2c_hwdata = {
> > @@ -662,6 +663,36 @@ static void i2c_imx_enable_bus_idle(struct imx_i2c_struct *i2c_imx)
> >       }
> >  }
> >
> > +static void i2c_imx_slave_event(struct imx_i2c_struct *i2c_imx,
> > +                             enum i2c_slave_event event, u8 *val)
> > +{
> > +     i2c_slave_event(i2c_imx->slave, event, val);
> > +     i2c_imx->last_slave_event = event;
> > +}
> > +
> > +static void i2c_imx_slave_finish_op(struct imx_i2c_struct *i2c_imx)
> > +{
> > +     u8 val;
> > +
> > +     while (i2c_imx->last_slave_event != I2C_SLAVE_STOP) {
> > +             switch (i2c_imx->last_slave_event) {
> > +             case I2C_SLAVE_READ_REQUESTED:
> > +                     i2c_imx_slave_event(i2c_imx, I2C_SLAVE_READ_PROCESSED,
> > +                                         &val);
> > +                     break;
> > +
> > +             case I2C_SLAVE_WRITE_REQUESTED:
> > +             case I2C_SLAVE_READ_PROCESSED:
> > +             case I2C_SLAVE_WRITE_RECEIVED:
> > +                     i2c_imx_slave_event(i2c_imx, I2C_SLAVE_STOP, &val);
> > +                     break;
> > +
> > +             case I2C_SLAVE_STOP:
> > +                     break;
> > +             }
> > +     }
> > +}
>
> Is it really working code?
>
> The i2c_imx_slave_finish_op() is a waiting busy loop withing an IRQ! And
> it is waiting for an event, which is updated in the same IRQ callback.
> Or am i missing some thing?
>
> Regards,
> Oleksij
>
> >  static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
> >                                    unsigned int status, unsigned int ctl)
> >  {
> > @@ -674,9 +705,11 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
> >       }
> >
> >       if (status & I2SR_IAAS) { /* Addressed as a slave */
> > +             i2c_imx_slave_finish_op(i2c_imx);
> >               if (status & I2SR_SRW) { /* Master wants to read from us*/
> >                       dev_dbg(&i2c_imx->adapter.dev, "read requested");
> > -                     i2c_slave_event(i2c_imx->slave, I2C_SLAVE_READ_REQUESTED, &value);
> > +                     i2c_imx_slave_event(i2c_imx,
> > +                                         I2C_SLAVE_READ_REQUESTED, &value);
> >
> >                       /* Slave transmit */
> >                       ctl |= I2CR_MTX;
> > @@ -686,7 +719,8 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
> >                       imx_i2c_write_reg(value, i2c_imx, IMX_I2C_I2DR);
> >               } else { /* Master wants to write to us */
> >                       dev_dbg(&i2c_imx->adapter.dev, "write requested");
> > -                     i2c_slave_event(i2c_imx->slave, I2C_SLAVE_WRITE_REQUESTED, &value);
> > +                     i2c_imx_slave_event(i2c_imx,
> > +                                         I2C_SLAVE_WRITE_REQUESTED, &value);
> >
> >                       /* Slave receive */
> >                       ctl &= ~I2CR_MTX;
> > @@ -697,17 +731,20 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
> >       } else if (!(ctl & I2CR_MTX)) { /* Receive mode */
> >               if (status & I2SR_IBB) { /* No STOP signal detected */
> >                       value = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
> > -                     i2c_slave_event(i2c_imx->slave, I2C_SLAVE_WRITE_RECEIVED, &value);
> > +                     i2c_imx_slave_event(i2c_imx,
> > +                                         I2C_SLAVE_WRITE_RECEIVED, &value);
> >               } else { /* STOP signal is detected */
> >                       dev_dbg(&i2c_imx->adapter.dev,
> >                               "STOP signal detected");
> > -                     i2c_slave_event(i2c_imx->slave, I2C_SLAVE_STOP, &value);
> > +                     i2c_imx_slave_event(i2c_imx,
> > +                                         I2C_SLAVE_STOP, &value);
> >               }
> >       } else if (!(status & I2SR_RXAK)) { /* Transmit mode received ACK */
> >               ctl |= I2CR_MTX;
> >               imx_i2c_write_reg(ctl, i2c_imx, IMX_I2C_I2CR);
> >
> > -             i2c_slave_event(i2c_imx->slave, I2C_SLAVE_READ_PROCESSED, &value);
> > +             i2c_imx_slave_event(i2c_imx,
> > +                                 I2C_SLAVE_READ_PROCESSED, &value);
> >
> >               imx_i2c_write_reg(value, i2c_imx, IMX_I2C_I2DR);
> >       } else { /* Transmit mode received NAK */
> > @@ -748,6 +785,7 @@ static int i2c_imx_reg_slave(struct i2c_client *client)
> >               return -EBUSY;
> >
> >       i2c_imx->slave = client;
> > +     i2c_imx->last_slave_event = I2C_SLAVE_STOP;
> >
> >       /* Resume */
> >       ret = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
> > @@ -800,10 +838,17 @@ static irqreturn_t i2c_imx_isr(int irq, void *dev_id)
> >
> >       status = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
> >       ctl = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> > +
> >       if (status & I2SR_IIF) {
> >               i2c_imx_clear_irq(i2c_imx, I2SR_IIF);
> > -             if (i2c_imx->slave && !(ctl & I2CR_MSTA))
> > -                     return i2c_imx_slave_isr(i2c_imx, status, ctl);
> > +             if (i2c_imx->slave) {
> > +                     if (!(ctl & I2CR_MSTA)) {
> > +                             return i2c_imx_slave_isr(i2c_imx, status, ctl);
> > +                     } else if (i2c_imx->last_slave_event !=
> > +                                I2C_SLAVE_STOP) {
> > +                             i2c_imx_slave_finish_op(i2c_imx);
> > +                     }
> > +             }
> >               return i2c_imx_master_isr(i2c_imx, status);
> >       }
> >
> > --
> > 2.25.1
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
>
> --
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