[PATCH v2 3/7] i2c: of-prober: skip post-power-on delay if already powered on

[Chen-Yu Tsai]

On some devices the I2C component is powered from an always-on power
rail, or the power rail has been left on by either POR defaults or
the bootloader. By the time the prober probes the device, the device
most certainly has finished initializing and can respond. There is no
need for the delay.

In such designs, the system integrators tend to work around the delay
to avoid the boot time penalty by simply omitting it from the device
tree and the component prober. This is undesired, as the device tree
is not fully describing the hardware.

Instead, check if the regulator supplies are all enabled, and skip
the post-power-on delay if that is the case.

Signed-off-by: Chen-Yu Tsai <wenst at chromium.org>
---
 drivers/i2c/i2c-core-of-prober.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core-of-prober.c b/drivers/i2c/i2c-core-of-prober.c
index 6a82b03809d4..f274e260353c 100644
--- a/drivers/i2c/i2c-core-of-prober.c
+++ b/drivers/i2c/i2c-core-of-prober.c
@@ -18,6 +18,7 @@
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 #include <linux/stddef.h>
+#include <linux/string_choices.h>
 
 /*
  * Some devices, such as Google Hana Chromebooks, are produced by multiple
@@ -219,19 +220,25 @@ static void i2c_of_probe_simple_put_supply(struct i2c_of_probe_simple_ctx *ctx)
 
 static int i2c_of_probe_simple_enable_regulator(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
 {
+	bool supply_was_on;
 	int ret;
 
 	if (!ctx->supply)
 		return 0;
 
-	dev_dbg(dev, "Enabling regulator supply \"%s\"\n", ctx->opts->supply_name);
+	supply_was_on = regulator_is_enabled(ctx->supply);
+
+	dev_dbg(dev, "Enabling regulator supply \"%s\" (was %s)\n", ctx->opts->supply_name,
+		str_on_off(supply_was_on));
 
 	ret = regulator_enable(ctx->supply);
 	if (ret)
 		return ret;
 
-	if (ctx->opts->post_power_on_delay_ms)
+	if (!supply_was_on && ctx->opts->post_power_on_delay_ms) {
+		dev_dbg(dev, "Waiting after enabling regulator\n");
 		msleep(ctx->opts->post_power_on_delay_ms);
+	}
 
 	return 0;
 }
-- 
2.55.0.rc0.799.gd6f94ed593-goog