Viresh Kumar wrote:
> Add i2c bus recovery infrastructure to i2c adapters as specified in
the i2c
> protocol Rev. 03 section 3.1.16 titled "Bus clear".
>
> http://www.nxp.com/documents/user_manual/UM10204.pdf
You should also take note of section 3.1.14 and its notes on Software
Reset -
"Precautions must be taken to ensure that a device is not
pulling down the SDA or SCL line after applying the supply
voltage, since these low levels would block the bus"
> Sometimes during operation i2c bus hangs and we need to give dummy
clocks to
> slave device to start the transfer again. Now we may have capability
in the bus
> controller to generate these clocks or platform may have gpio pins
which can be
> toggled to generate dummy clocks. This patch supports both.
I may have missed it but misses an I2C check step, but that could be
because I do so much embedded and hardware side as well.
> This patch also adds in generic bus recovery routines gpio or scl
line based
> which can be used by bus controller. In addition controller driver
may provide
> its own version of the bus recovery routine.
>
> This doesn't support multi-master recovery for now.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>
> Hi Wolfram,
>
> I am sending V7 before closing our comments completely on V6 (Very
few are left
> now :) ), so that you can get an idea of what i am implementing now. It
> incorporates all your comments leaving:
.....
> +static int i2c_get_gpios_for_recovery(struct i2c_adapter *adap)
> +{
> + struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> + struct device *dev = &adap->dev;
> + int ret = 0;
Where is the check that SCL is NOT low (bus fault or device doing clock
stretching)
> + ret = gpio_request_one(bri->scl_gpio, GPIOF_OPEN_DRAIN |
> + GPIOF_OUT_INIT_HIGH, "i2c-scl");
I always get wary of people driving I2C with non-open-drain, especially
with stuck busses
> + if (ret) {
> + dev_warn(dev, "gpio request fail: %d\n", bri->scl_gpio);
> + return ret;
> + }
> +
> + if (!bri->skip_sda_polling) {
> + if (gpio_request_one(bri->sda_gpio, GPIOF_IN, "i2c-sda")) {
> + /* work without sda polling */
> + dev_warn(dev, "can't get sda: %d. Skip sda polling\n",
> + bri->sda_gpio);
> + bri->skip_sda_polling = true;
> + }
> + }
> +
> + return ret;
> +}
.....
> +static int i2c_generic_recovery(struct i2c_adapter *adap)
> +{
> + struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> + unsigned long delay = 1000000; /* 106/KHz for delay in ns */
> + int i, val = 0;
> +
> + if (bri->prepare_recovery)
> + bri->prepare_recovery(bri);
> +
> + /*
> + * By this time SCL is high, as we need to give 9 falling-rising
edges
> + */
In my view that needs to be done by an actual check of the real SCL not
assumption.
> + delay = DIV_ROUND_UP(delay, bri->clock_rate_khz * 2);
> +
> + for (i = 0; i < RECOVERY_CLK_CNT * 2; i++, val = !val) {
> + bri->set_scl(adap, val);
> + ndelay(delay);
> +
> + /* break if sda got high, check only when scl line is high */
> + if (!bri->skip_sda_polling && val)
Dont use 'val' read the actual SCL line which ensures you you are not
wasting your time because of hardware fault. Possibly saving your GPIO
from being stuck permanently.
> + if (unlikely(bri->get_sda(adap)))
> + break;
> + }
> +
> + if (bri->unprepare_recovery)
> + bri->unprepare_recovery(bri);
> +
> + return 0;
> +}
--
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