OCPC: Calculate system & battery resistance

In order to optimize charging from the auxiliary charger, we need to
calculate the system resistance as well as the battery resistance.
This allows some charger ICs to compensate for the losses from their
output node to the battery.

In order to perform this calculation, we must do it when the AP is off
(or in suspend) which provides the condition that nearly all of the
charge current is entering the battery and isn't being largely
consumed by the rest of the system.  The combined Rsys+Rbatt
calculation is relatively straightforward as it's the delta between
the VSYS output and the battery voltage divided by the current
entering the battery.  In order to separate out the two terms, we can
look at the delta between the VSYS output and the VSYS node that's
connected to the BFET as well as look at the egress current from the
auxiliary charger and the current entering the battery.

This commit adds this system resistance measurements and enables it
for the RAA489000.  The resistances are updated in S5/G3 when charging
from the auxiliary charger every ~2.4s.

BUG=b:148980020
BRANCH=None
TEST=Build and flash waddledoo, verify that charging continues to work
in all power states and battery can become full.
TEST=Verify that charge current is still close to the target without
excessively exceeding it.
TEST=Verify charging in constant load via `stressapptest`.
TEST=Verify charging in bursty workload via `stressapptest` with
pauses for power spikes while monitoring charge current with a current
probe.
TEST=Verify charging works out of battery cutoff from the auxiliary
charger.

Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Change-Id: I1faa3a0b2b3d8f4fd44d72cd1f546226268df0c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2290058
Reviewed-by: Diana Z <dzigterman@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Commit-Queue: Aseda Aboagye <aaboagye@chromium.org>

1 files changed, 10 insertions, 9 deletions

diff --git a/driver/charger/isl923x.c b/driver/charger/isl923x.c
index 797cac170d..fb6f60a8ed 100644
--- a/driver/charger/isl923x.c
+++ b/driver/charger/isl923x.c
@@ -1042,16 +1042,17 @@ static enum ec_error_list raa489000_set_vsys_compensation(int chgnum,
 
 	/*
 	 * Rp1 is set between 36-156mOhms in 4mOhm increments.  This must be
-	 * non-zero in order for compensation to work.  The system keeps track
-	 * of combined resistance; we'll assume that Rp2 is what was statically
-	 * defined leaving Rp1 as the difference.  If Rp1 is less than 36mOhms,
-	 * then the compensation is disabled.
+	 * non-zero in order for compensation to work.
 	 *
-	 * TODO(b/148980020): When we can calculate Rsys vs Rbatt, update this
-	 * accordingly.
+	 * To get Rp1, we need to look at the delta between VSYS measured by the
+	 * auxiliary charger IC and the primary charger IC where the actual VSYS
+	 * node is as well as the current provided by the auxiliary charger IC.
+	 * The system keeps track of combined resistance; therefore, Rp2 is the
+	 * difference between the combined resistance and Rp1 that we calculate.
+	 * If Rp1 is less than 36mOhms, then the compensation is disabled.
 	 */
-	rp1 = o->combined_rsys_rbatt_mo - CONFIG_OCPC_DEF_RBATT_MOHMS;
-	rp1 = MIN(rp1, RAA489000_RP1_MAX);
+
+	rp1 = MIN(o->rsys_mo, RAA489000_RP1_MAX);
 	rp1 -= RAA489000_RP1_MIN;
 	if (rp1 < 0) {
 		if (o->last_vsys == OCPC_UNINIT)
@@ -1064,7 +1065,7 @@ static enum ec_error_list raa489000_set_vsys_compensation(int chgnum,
 	}
 
 	/* Rp2 is set between 0-124mOhms in 4mOhm increments. */
-	rp2 = CONFIG_OCPC_DEF_RBATT_MOHMS;
+	rp2 = o->rbatt_mo;
 	rp2 = CLAMP(rp2, RAA489000_RP2_MIN, RAA489000_RP2_MAX);
 	rp2 /= 4;