NFC: trf7970a: Add quirk to keep EN2 low

 * The trf7970a is very timing sensitive and the VIN, EN2, and EN

 * pins must asserted in that order and with specific delays in between.

 * The delays used in the driver were provided by TI and have been

 * confirmed to work with this driver.

 * confirmed to work with this driver.  There is a bug with the current

 * version of the trf7970a that requires that EN2 remain low no matter

 * what.  If it goes high, it will generate an RF field even when in

 * passive target mode.  TI has indicated that the chip will work okay

 * when EN2 is left low.  The 'en2-rf-quirk' device tree property

 * indicates that trf7970a currently being used has the erratum and

 * that EN2 must be kept low.

 *

 * Timeouts are implemented using the delayed workqueue kernel facility.

 * Timeouts are required so things don't hang when there is no response

 * read continuous command for IRQ Status and Collision Position registers.

 */

#define TRF7970A_QUIRK_IRQ_STATUS_READ		BIT(0)

#define TRF7970A_QUIRK_EN2_MUST_STAY_LOW	BIT(1)

/* Direct commands */

#define TRF7970A_CMD_IDLE			0x00

		return ret;

	}

	if (of_property_read_bool(np, "en2-rf-quirk"))

		trf->quirks |= TRF7970A_QUIRK_EN2_MUST_STAY_LOW;

	ret = devm_request_threaded_irq(trf->dev, spi->irq, NULL,

			trf7970a_irq, IRQF_TRIGGER_RISING | IRQF_ONESHOT,

			"trf7970a", trf);

	usleep_range(5000, 6000);

	if (!(trf->quirks & TRF7970A_QUIRK_EN2_MUST_STAY_LOW)) {

		gpio_set_value(trf->en2_gpio, 1);

		usleep_range(1000, 2000);

	}

	gpio_set_value(trf->en_gpio, 1);

	usleep_range(20000, 21000);