mmc: pwrseq_simple: Parse DTS for the power-off-delay-us property

If the optional power-off-delay-us property is found, insert the
corresponding delay after asserting the GPIO during power off. This enables
a graceful shutdown sequence for some devices.

Cc: [e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>

drivers/mmc/core/pwrseq_simple.c

···
 	struct mmc_pwrseq pwrseq;
 	bool clk_enabled;
 	u32 post_power_on_delay_ms;
+	u32 power_off_delay_us;
 	struct clk *ext_clk;
 	struct gpio_descs *reset_gpios;
 };
···
 
 	mmc_pwrseq_simple_set_gpios_value(pwrseq, 1);
 
+	if (pwrseq->power_off_delay_us)
+		usleep_range(pwrseq->power_off_delay_us,
+			2 * pwrseq->power_off_delay_us);
+
 	if (!IS_ERR(pwrseq->ext_clk) && pwrseq->clk_enabled) {
 		clk_disable_unprepare(pwrseq->ext_clk);
 		pwrseq->clk_enabled = false;
···
 
 	device_property_read_u32(dev, "post-power-on-delay-ms",
 				 &pwrseq->post_power_on_delay_ms);
+	device_property_read_u32(dev, "power-off-delay-us",
+				 &pwrseq->power_off_delay_us);
 
 	pwrseq->pwrseq.dev = dev;
 	pwrseq->pwrseq.ops = &mmc_pwrseq_simple_ops;