linux-kernel - Re: [PATCH v6 08/19] i2c: octeon: Enable High-Level Controller

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Message-ID: <20160420214354.GD1546@katana>
Date:	Wed, 20 Apr 2016 23:43:54 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Jan Glauber <jglauber@...ium.com>
Cc:	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	David Daney <ddaney@...iumnetworks.com>
Subject: Re: [PATCH v6 08/19] i2c: octeon: Enable High-Level Controller

On Mon, Apr 11, 2016 at 05:28:39PM +0200, Jan Glauber wrote:
> From: David Daney <ddaney@...iumnetworks.com>
> 
> Use High-Level Controller (HLC) when possible. The HLC can read/write
> up to 8 bytes and is completely optional. The most important difference
> of the HLC is that it only requires one interrupt for a transfer
> (up to 8 bytes) where the low-level read/write requires 2 interrupts
> plus one interrupt per transferred byte. Since the interrupts are costly
> using the HLC improves the performance. Also, the HLC provides improved error
> handling.

Much better description, thanks!

> +	while (1) {
> +		val = octeon_i2c_ctl_read(i2c);
> +		if (!(val & (TWSI_CTL_STA | TWSI_CTL_STP)));
> +			break;
> +
> +		/* clear IFLG event */
> +		if (val & TWSI_CTL_IFLG)
> +			octeon_i2c_ctl_write(i2c, TWSI_CTL_ENAB);
> +
> +		if (try++ > 100) {
> +			pr_err("%s: giving up\n", __func__);
> +			break;
> +		}
> +
> +		/* spin until any start/stop has finished */
> +		udelay(10);
> +	}

Maybe you can use one of the readx_poll_timeout() functions?

> +/**
> + * octeon_i2c_hlc_wait - wait for an HLC operation to complete
> + * @i2c: The struct octeon_i2c
> + *
> + * Returns 0 on success, otherwise a negative errno.
> + */
> +static int octeon_i2c_hlc_wait(struct octeon_i2c *i2c)
> +{
> +	int time_left;
> +
> +	octeon_i2c_hlc_int_enable(i2c);
> +	time_left = wait_event_interruptible_timeout(i2c->queue,
> +					octeon_i2c_hlc_test_ready(i2c),
> +					i2c->adap.timeout);

Have you tested signal handling thoroughly? Most driver dropped the
_interruptible after a while. Mostly they found out that the state
machine of the interrupt handler couldn't gracefully deal with it and
nobody really needed the interruptible. Just saying.

> +	octeon_i2c_int_disable(i2c);
> +	if (!time_left) {
> +		octeon_i2c_hlc_int_clear(i2c);
> +		dev_dbg(i2c->dev, "%s: timeout\n", __func__);
> +		return -ETIMEDOUT;
> +	}
> +
> +	if (time_left < 0) {
> +		dev_dbg(i2c->dev, "%s: wait interrupted\n", __func__);
> +		return time_left;
> +	}
> +	return 0;
> +}

Drop the debug messages?

I can't say much about the HW details, of course. Didn't spot anything
suspicious there.


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