linux-kernel - Re: [PATCH v5 2/2] i2c: add support for Socionext SynQuacer I2C controller

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Date:   Sun, 25 Mar 2018 11:30:21 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v5 2/2] i2c: add support for Socionext SynQuacer I2C controller

On 24 March 2018 at 23:19, Wolfram Sang <wsa@...-dreams.de> wrote:
> Hi Ard,
>
>> +static int synquacer_i2c_master_start(struct synquacer_i2c *i2c,
>> +                                   struct i2c_msg *pmsg)
>> +{
>> +     unsigned char bsr, bcr;
>> +
>> +     if (pmsg->flags & I2C_M_RD)
>> +             writeb((pmsg->addr << 1) | 1,
>> +                    i2c->base + SYNQUACER_I2C_REG_DAR);
>> +     else
>> +             writeb(pmsg->addr << 1,
>> +                    i2c->base + SYNQUACER_I2C_REG_DAR);
>
> writeb(i2c_8bit_addr_from_msg(pmsg), i2c->base + SYNQUACER_I2C_REG_DAR);
>
> ?
>
>> +static int synquacer_i2c_master_recover(struct synquacer_i2c *i2c)
>> +{
>
> This is the bus recovery mechanism with toggling SCL pulses, right?
> That should be implemented using a 'struct i2c_bus_recovery_info' and
> the core helpers.
>
>> +static int synquacer_i2c_doxfer(struct synquacer_i2c *i2c,
>> +                             struct i2c_msg *msgs, int num)
>> +{
>> +     unsigned char bsr;
>> +     unsigned long timeout, bb_timeout;
>> +     int ret;
>> +
>> +     if (i2c->is_suspended)
>> +             return -EBUSY;
>> +
>> +     synquacer_i2c_hw_init(i2c);
>> +     bsr = readb(i2c->base + SYNQUACER_I2C_REG_BSR);
>> +     if (bsr & SYNQUACER_I2C_BSR_BB) {
>> +             dev_err(i2c->dev, "cannot get bus (bus busy)\n");
>> +             return -EBUSY;
>> +     }
>> +
>> +     init_completion(&i2c->completion);
>
> reinit_completion? And init_completion() in probe()?
>
>> +     /* ensure the stop has been through the bus */
>> +     bb_timeout = jiffies + HZ;
>> +     do {
>> +             bsr = readb(i2c->base + SYNQUACER_I2C_REG_BSR);
>> +             if (!(bsr & SYNQUACER_I2C_BSR_BB))
>> +                     return 0;
>> +     } while (time_before(jiffies, bb_timeout));
>
> Busy looping for one second? And won't the bus_free detection at the
> beginning of a transfer do?
>
>> +static int synquacer_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>> +                           int num)
>> +{
>> +     struct synquacer_i2c *i2c;
>> +     int retry;
>> +     int ret;
>> +
>> +     if (!msgs)
>> +             return -EINVAL;
>> +     if (num <= 0)
>> +             return -EINVAL;
>
> Hmm, this should be done by the core. I am surprised it doesn't do that yet :/
>
>> +
>> +     i2c = i2c_get_adapdata(adap);
>> +     i2c->timeout_ms = calc_timeout_ms(i2c, msgs, num);
>> +
>> +     dev_dbg(i2c->dev, "calculated timeout %d ms\n", i2c->timeout_ms);
>> +
>> +     for (retry = 0; retry < adap->retries; retry++) {
>> +
>> +             ret = synquacer_i2c_doxfer(i2c, msgs, num);
>> +             if (ret != -EAGAIN)
>> +                     return ret;
>> +
>> +             dev_dbg(i2c->dev, "Retrying transmission (%d)\n", retry);
>> +
>> +             synquacer_i2c_master_recover(i2c);
>
> Recovery is only when SDA is stuck low, held by a client. That is
> nothing you should do just on any error.
>
> If you want the driver in v4.17, I'd suggest to drop
> synquacer_i2c_master_recover() now and add it incrementally later, using
> the existing recovery infrastructure. The rest is only minor stuff and
> needs not much further discussion IMO.
>

Thanks Wolfram.

I have fixed all these up and am about to send out the v6.