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

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Date:   Sun, 25 Mar 2018 00:19:10 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     robh+dt@...nel.org, mark.rutland@....com,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jassisinghbrar@...il.com, andy.shevchenko@...il.com
Subject: Re: [PATCH v5 2/2] i2c: add support for Socionext SynQuacer I2C
 controller

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.

Regards,

   Wolfram


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