[PATCH v2 1/2] power: supply: sbs-battery: don't assume MANUFACTURER_DATA formats

[Brian Norris]

This driver was originally submitted for the TI BQ20Z75 battery IC
(commit a7640bfa10c5 ("power_supply: Add driver for TI BQ20Z75 gas gauge
IC")) and later renamed to express generic SBS support. While it's
mostly true that this driver implemented a standard SBS command set, it
takes liberties with the REG_MANUFACTURER_DATA register. This register
is specified in the SBS spec, but it doesn't make any mention of what
its actual contents are.

We've sort of noticed this optionality previously, with commit
17c6d3979e5b ("sbs-battery: make writes to ManufacturerAccess
optional"), where we found that some batteries NAK writes to this
register.

What this really means is that so far, we've just been lucky that most
batteries have either been compatible with the TI chip, or else at least
haven't reported highly-unexpected values.

For instance, one battery I have here seems to report either 0x0000 or
0x0100 to the MANUFACTURER_ACCESS_STATUS command -- while this seems to
match either Wake Up (bits[11:8] = 0000b) or Normal Discharge
(bits[11:8] = 0001b) status for the TI part [1], they don't seem to
actually correspond to real states (for instance, I never see 0101b =
Charge, even when charging).

On other batteries, I'm getting apparently random data in return, which
means that occasionally, we interpret this as "battery not present" or
"battery is not healthy".

All in all, it seems to be a really bad idea to make assumptions about
REG_MANUFACTURER_DATA, unless we already know what battery we're using.
Therefore, this patch reimplements the "present" and "health" checks to
the following on most SBS batteries:

1. HEALTH: report "unknown" -- I couldn't find a standard SBS command
   that gives us much useful here
2. PRESENT: just send a REG_STATUS command; if it succeeds, then the
   battery is present

Also, we stop sending MANUFACTURER_ACCESS_SLEEP to non-TI parts. I have
no proof that this is useful and supported.

If someone explicitly provided a 'ti,bq20z75' compatible property, then
we retain the existing TI command behaviors.

[1] http://www.ti.com/lit/er/sluu265a/sluu265a.pdf

Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
---
v2:
 * don't stub out POWER_SUPPLY_PROP_PRESENT from sbs_data[]
 * use if/else instead of switch/case
---
 drivers/power/supply/sbs-battery.c | 54 +++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 8 deletions(-)

diff --git a/drivers/power/supply/sbs-battery.c b/drivers/power/supply/sbs-battery.c
index 83d7b4115857..8dea63464a3f 100644
--- a/drivers/power/supply/sbs-battery.c
+++ b/drivers/power/supply/sbs-battery.c
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/power/sbs-battery.h>
 #include <linux/power_supply.h>
 #include <linux/slab.h>
@@ -156,6 +157,9 @@ static enum power_supply_property sbs_properties[] = {
 	POWER_SUPPLY_PROP_MODEL_NAME
 };
 
+/* Supports special manufacturer commands from TI BQ20Z75 IC. */
+#define SBS_FLAGS_TI_BQ20Z75		BIT(0)
+
 struct sbs_info {
 	struct i2c_client		*client;
 	struct power_supply		*power_supply;
@@ -168,6 +172,7 @@ struct sbs_info {
 	u32				poll_retry_count;
 	struct delayed_work		work;
 	struct mutex			mode_lock;
+	u32				flags;
 };
 
 static char model_name[I2C_SMBUS_BLOCK_MAX + 1];
@@ -315,6 +320,27 @@ static int sbs_status_correct(struct i2c_client *client, int *intval)
 static int sbs_get_battery_presence_and_health(
 	struct i2c_client *client, enum power_supply_property psp,
 	union power_supply_propval *val)
+{
+	int ret;
+
+	if (psp == POWER_SUPPLY_PROP_PRESENT) {
+		/* Dummy command; if it succeeds, battery is present. */
+		ret = sbs_read_word_data(client, sbs_data[REG_STATUS].addr);
+		if (ret < 0)
+			val->intval = 0; /* battery disconnected */
+		else
+			val->intval = 1; /* battery present */
+		return 0;
+	} else { /* POWER_SUPPLY_PROP_HEALTH */
+		/* SBS spec doesn't have a general health command. */
+		val->intval = POWER_SUPPLY_HEALTH_UNKNOWN;
+		return 0;
+	}
+}
+
+static int sbs_get_ti_battery_presence_and_health(
+	struct i2c_client *client, enum power_supply_property psp,
+	union power_supply_propval *val)
 {
 	s32 ret;
 
@@ -600,7 +626,12 @@ static int sbs_get_property(struct power_supply *psy,
 	switch (psp) {
 	case POWER_SUPPLY_PROP_PRESENT:
 	case POWER_SUPPLY_PROP_HEALTH:
-		ret = sbs_get_battery_presence_and_health(client, psp, val);
+		if (client->flags & SBS_FLAGS_TI_BQ20Z75)
+			ret = sbs_get_ti_battery_presence_and_health(client,
+								     psp, val);
+		else
+			ret = sbs_get_battery_presence_and_health(client, psp,
+								  val);
 		if (psp == POWER_SUPPLY_PROP_PRESENT)
 			return 0;
 		break;
@@ -806,6 +837,7 @@ static int sbs_probe(struct i2c_client *client,
 	if (!chip)
 		return -ENOMEM;
 
+	chip->flags = (u32)(uintptr_t)of_device_get_match_data(&client->dev);
 	chip->client = client;
 	chip->enable_detection = false;
 	psy_cfg.of_node = client->dev.of_node;
@@ -915,12 +947,15 @@ static int sbs_suspend(struct device *dev)
 	if (chip->poll_time > 0)
 		cancel_delayed_work_sync(&chip->work);
 
-	/*
-	 * Write to manufacturer access with sleep command.
-	 * Support is manufacturer dependend, so ignore errors.
-	 */
-	sbs_write_word_data(client, sbs_data[REG_MANUFACTURER_DATA].addr,
-		MANUFACTURER_ACCESS_SLEEP);
+	if (chip->flags & SBS_FLAGS_TI_BQ20Z75) {
+		/*
+		 * Write to manufacturer access with sleep command.
+		 * Support is manufacturer dependent, so ignore errors.
+		 */
+		sbs_write_word_data(client,
+				    sbs_data[REG_MANUFACTURER_DATA].addr,
+				    MANUFACTURER_ACCESS_SLEEP);
+	}
 
 	return 0;
 }
@@ -941,7 +976,10 @@ MODULE_DEVICE_TABLE(i2c, sbs_id);
 
 static const struct of_device_id sbs_dt_ids[] = {
 	{ .compatible = "sbs,sbs-battery" },
-	{ .compatible = "ti,bq20z75" },
+	{
+		.compatible = "ti,bq20z75",
+		.data = (void *)SBS_FLAGS_TI_BQ20Z75,
+	},
 	{ }
 };
 MODULE_DEVICE_TABLE(of, sbs_dt_ids);
-- 
2.17.0.921.gf22659ad46-goog