[S] Change in coreboot[main]: ec/google/chromeec: Add function to detect barrel charger

[Subrata Banik (Code Review)]

Subrata Banik has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/85765?usp=email )

Change subject: ec/google/chromeec: Add function to detect barrel charger
......................................................................

ec/google/chromeec: Add function to detect barrel charger

This commit introduces a new function,
google_chromeec_is_barrel_charger_present(), which checks if a barrel
charger is present.

The function uses the following logic to determine if a barrel charger
is present:

- If both a barrel charger and USB-C PD are present, then the barrel
charger takes precedence over USB-C PD. As a result,
google_chromeec_is_usb_pd_attached() will return false. This logic can
be used to deterministically say if a barrel charger is present even
when both a barrel charger and USB-C PD are attached.

- If an AC charger is detected and USB-C PD is not present, then a
barrel charger must be present.

This change allows the EC to accurately detect the presence of a barrel
charger, even when a USB-C PD charger is also attached.

BUG=b:377798581
TEST=Able to read the charger status correctly while booting
google/fatcat.

Experiment #1:
- USB-C PD Attached = yes
- Barrel Attached = No
- Charger Detected = Yes

```
fatcat-rev257 ~ # cbmem -c | grep -5 "ac_charger_present"
[INFO ]  ac_charger_present: yes
[INFO ]  usb_pd_present: yes
[INFO ]  baseboard_devtree_update: Barrel Absent
```

Experiment #2:
- USB-C PD Attached = No
- Barrel Attached = Yes
- Charger Detected = Yes

```
[INFO ]  ac_charger_present: yes
[INFO ]  usb_pd_present: no
[INFO ]  baseboard_devtree_update: Barrel Present
```

Experiment #3:
- USB-C PD Attached = Yes
- Barrel Attached = Yes
- Charger Detected = Yes

```
[INFO ]  ac_charger_present: yes
[INFO ]  usb_pd_present: no
[INFO ]  baseboard_devtree_update: Barrel Present
```

Experiment #4:
- USB-C PD Attached = No
- Barrel Attached = No
- Charger Detected = No

```
[INFO ]  ac_charger_present: no
[INFO ]  usb_pd_present: no
[INFO ]  baseboard_devtree_update: Barrel Absent
```

Change-Id: I9644f0dec057f95bb0a22cdc18edc1a0234ee3a9
Signed-off-by: Subrata Banik 
---
M src/ec/google/chromeec/ec.c
M src/ec/google/chromeec/ec.h
2 files changed, 36 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/65/85765/1

diff --git a/src/ec/google/chromeec/ec.c b/src/ec/google/chromeec/ec.c
index 502684c..670d557 100644
--- a/src/ec/google/chromeec/ec.c
+++ b/src/ec/google/chromeec/ec.c
@@ -1005,6 +1005,34 @@
    return false;
 }

+/*
+ * Using below scenarios to conclude if device has a barrel charger attached.
+ * +-----------+-----------------+------------------+---------------------------------+
+ * | Scenarios | Charger Present | USB-C PD Present | Conclusion: Barrel Present ?    |
+ * +-----------+-----------------+------------------+---------------------------------+
+ * |  #1       | Yes             | Yes              | Non Conclusive (comments below) |
+ * |  #2       | No              | Yes              | Not possible                    |
+ * |  #3       | Yes             | No               | Must be barrel charger          |
+ * |  #4       | No              | No               | Barrel not present              |
+ * +-----------+-----------------+------------------+---------------------------------+
+ */
+bool google_chromeec_is_barrel_charger_present(void)
+{
+	bool ac_charger_present = google_chromeec_is_charger_present();
+	bool usb_pd_present = google_chromeec_is_usb_pd_attached();
+
+	/*
+	 * If both barrel charger and USB-C PD present at once then barrel took the precedence
+	 * over USB-C PD as a result `google_chromeec_is_usb_pd_attached()` will return
+	 * `false`. This logic can be used further here to deterministically say if barrel
+	 * charger is present even when both barrel charger and USB-C PD attached.
+	 */
+	if (ac_charger_present == true && usb_pd_present == false)
+		return true;
+
+	return false;
+}
+
 int google_chromeec_override_dedicated_charger_limit(uint16_t current_lim,
    					     uint16_t voltage_lim)
 {
diff --git a/src/ec/google/chromeec/ec.h b/src/ec/google/chromeec/ec.h
index a50c311..c66db18 100644
--- a/src/ec/google/chromeec/ec.h
+++ b/src/ec/google/chromeec/ec.h
@@ -148,6 +148,14 @@
  */
 bool google_chromeec_is_charger_present(void);

+/**
+ * Check if barrel charger is present.
+ *
+ * @return		true: if the barrel_charger is present
+ *			false: if the barrel_charger is not present
+ */
+bool google_chromeec_is_barrel_charger_present(void);
+
 /*
  * Set max current and voltage of a dedicated charger.
  *