Re: [PATCH v2 2/4] platform: arm64: dell-xps-ec: new driver

[Aleksandrs Vinarskis]

On Sunday, April 5th, 2026 at 02:29, Bryan O'Donoghue <bryan.odonoghue@xxxxxxxxxx> wrote:

> On 04/04/2026 13:55, Aleksandrs Vinarskis wrote:
> > Introduce EC driver for Dell XPS 13 9345 (codename 'tributo') which may
> > partially of fully compatible with Snapdragon-based Dell Latitude,
> > Inspiron ('thena'). Primary function of this driver is unblock EC's
> > thermal management, specifically to provide it with necessary
> > information to control device fans, peripherals power.
> >
> > The driver was developed primarily by analyzing ACPI DSDT's _DSM and
> > i2c dumps of communication between SoC and EC. Changes to Windows
> > driver's behavior include increasing temperature feed loop from ~50ms
> > to 100ms here.
> >
> > While Xps's EC is rather complex and controls practically all device
> > peripherals including touch row's brightness and special keys such as
> > mic mute, these do not go over this particular i2c interface.
> >
> > Not yet implemented features:
> > - On lid-close IRQ event is registered. Windows performs what to
> >    appears to be thermistor constants readout, though its not obvious
> >    what it used for.
> > - According to ACPI's _DSM there is a method to readout fans' RPM.
> > - Initial thermistor constants were sniffed from Windows, these can be
> >    likely fine tuned for better cooling performance.
> > - There is additional temperature reading that Windows sents to EC but
> >    more rare than others, likely SoC T_j / TZ98 or TZ4. This is the only
> >    thermal zone who's reading can exceed 115C without triggering thermal
> >    shutdown.
> > - Given similarities between 'tributo' and 'thena' platforms, including
> >    EC i2c address, driver can be potentially extended to support both.
> >
> > Signed-off-by: Aleksandrs Vinarskis <alex@xxxxxxxxxxxxx>
> > ---
> >   MAINTAINERS                          |   1 +
> >   drivers/platform/arm64/Kconfig       |  12 ++
> >   drivers/platform/arm64/Makefile      |   1 +
> >   drivers/platform/arm64/dell-xps-ec.c | 267 +++++++++++++++++++++++++++++++++++
> >   4 files changed, 281 insertions(+)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index a5d175559f4468dfe363b319a1b08d3425f4d712..c150f57b60706224e5b24b0dfb3d8a9b81f36398 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -7240,6 +7240,7 @@ DELL XPS EMBEDDED CONTROLLER DRIVER
> >   M:	Aleksandrs Vinarskis <alex@xxxxxxxxxxxxx>
> >   S:	Maintained
> >   F:	Documentation/devicetree/bindings/embedded-controller/dell,xps13-9345-ec.yaml
> > +F:	drivers/platform/arm64/dell-xps-ec.c
> >
> >   DELTA AHE-50DC FAN CONTROL MODULE DRIVER
> >   M:	Zev Weiss <zev@xxxxxxxxxxxxxxxxx>
> > diff --git a/drivers/platform/arm64/Kconfig b/drivers/platform/arm64/Kconfig
> > index 10f905d7d6bfa5fad30a0689d3a20481268c781e..0bc8f016032bb05cb3a7cc50bdf1092da04153bc 100644
> > --- a/drivers/platform/arm64/Kconfig
> > +++ b/drivers/platform/arm64/Kconfig
> > @@ -33,6 +33,18 @@ config EC_ACER_ASPIRE1
> >   	  laptop where this information is not properly exposed via the
> >   	  standard ACPI devices.
> >
> > +config EC_DELL_XPS
> > +	tristate "Dell XPS 9345 Embedded Controller driver"
> > +	depends on ARCH_QCOM || COMPILE_TEST
> > +	depends on I2C
> > +	depends on IIO
> > +	help
> > +	  Driver for the Embedded Controller in the Qualcomm Snapdragon-based
> > +	  Dell XPS 13 9345, which handles thermal management and fan speed
> > +	  control.
> > +
> > +	  Say M or Y here to include this support.
> > +
> >   config EC_HUAWEI_GAOKUN
> >   	tristate "Huawei Matebook E Go Embedded Controller driver"
> >   	depends on ARCH_QCOM || COMPILE_TEST
> > diff --git a/drivers/platform/arm64/Makefile b/drivers/platform/arm64/Makefile
> > index 60c131cff6a15bb51a49c9edab95badf513ee0f6..6768dc6c2310837374e67381cfc729bed1fdaaef 100644
> > --- a/drivers/platform/arm64/Makefile
> > +++ b/drivers/platform/arm64/Makefile
> > @@ -6,6 +6,7 @@
> >   #
> >
> >   obj-$(CONFIG_EC_ACER_ASPIRE1)	+= acer-aspire1-ec.o
> > +obj-$(CONFIG_EC_DELL_XPS)	+= dell-xps-ec.o
> >   obj-$(CONFIG_EC_HUAWEI_GAOKUN)	+= huawei-gaokun-ec.o
> >   obj-$(CONFIG_EC_LENOVO_YOGA_C630) += lenovo-yoga-c630.o
> >   obj-$(CONFIG_EC_LENOVO_THINKPAD_T14S) += lenovo-thinkpad-t14s.o
> > diff --git a/drivers/platform/arm64/dell-xps-ec.c b/drivers/platform/arm64/dell-xps-ec.c
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..bf1495fbe473ccdb82b95a66b56e8525f782cc8e
> > --- /dev/null
> > +++ b/drivers/platform/arm64/dell-xps-ec.c
> > @@ -0,0 +1,267 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (c) 2026, Aleksandrs Vinarskis <alex@xxxxxxxxxxxxx>
> > + */
> > +
> > +#include <linux/array_size.h>
> > +#include <linux/dev_printk.h>
> > +#include <linux/device.h>
> > +#include <linux/devm-helpers.h>
> > +#include <linux/err.h>
> > +#include <linux/i2c.h>
> > +#include <linux/iio/consumer.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/jiffies.h>
> > +#include <linux/module.h>
> > +#include <linux/pm.h>
> > +#include <linux/unaligned.h>
> > +#include <linux/workqueue.h>
> > +
> > +#define DELL_XPS_EC_SUSPEND_CMD		0xb9
> > +#define DELL_XPS_EC_SUSPEND_MSG_LEN	64
> > +
> > +#define DELL_XPS_EC_TEMP_CMD0		0xfb
> > +#define DELL_XPS_EC_TEMP_CMD1		0x20
> > +#define DELL_XPS_EC_TEMP_CMD3		0x02
> > +#define DELL_XPS_EC_TEMP_MSG_LEN	6
> > +#define DELL_XPS_EC_TEMP_POLL_JIFFIES	msecs_to_jiffies(100)
> > +
> > +/*
> > + * Format:
> > + * - header/unknown (2 bytes)
> > + * - per-thermistor entries (3 bytes): thermistor_id, param1, param2
> > + */
> > +static const u8 dell_xps_ec_thermistor_profile[] = {
> > +	0xff, 0x54,
> > +	0x01, 0x00, 0x2b,	/* sys_therm0 */
> > +	0x02, 0x44, 0x2a,	/* sys_therm1 */
> > +	0x03, 0x44, 0x2b,	/* sys_therm2 */
> > +	0x04, 0x44, 0x28,	/* sys_therm3 */
> > +	0x05, 0x55, 0x2a,	/* sys_therm4 */
> > +	0x06, 0x44, 0x26,	/* sys_therm5 */
> > +	0x07, 0x44, 0x2b,	/* sys_therm6 */
> > +};
> > +
> > +/*
> > + * Mapping from IIO channel name to EC command byte
> > + */
> > +static const struct {
> > +	const char *name;
> > +	u8 cmd;
> > +} dell_xps_ec_therms[] = {
> > +	/* TODO: 0x01 is sent only occasionally, likely TZ98 or TZ4 */
> > +	{ "sys_therm0", 0x02 },
> > +	{ "sys_therm1", 0x03 },
> > +	{ "sys_therm2", 0x04 },
> > +	{ "sys_therm3", 0x05 },
> > +	{ "sys_therm4", 0x06 },
> > +	{ "sys_therm5", 0x07 },
> > +	{ "sys_therm6", 0x08 },
> > +};
>
> You could probably retrieve these strings from the dt if you really need
> them.
>
> I don't think you need static consts in your driver though you could
> just as easily do `sprintf("sys_therm%d\n", i) where you use
> ec_therms[i].name - the name is only used to print errors and you have
> the index of the channel when you do.
>
> It would be nicer to get the strings from DT - certainly make the string
> names mandatory but, then let the DT specify those names.
>
> Either that or just do the sprintf("sys_therm%d\n", i); for the index,
> whichever you wish yourself.

Hi Bryan,

Will answer here to all three comments about `sys_thermX`.

The reason I have added them as static consts here, and defined them in
the schema is because the order of the channels matters:
1. On my XPS (UEFI v2.11.0) changes in sys_therm2 immediately result in
   changes in fan speeds. Other channels seemingly have no affect, at
   least when spoofed one by one, implying that EC cares which value
   is which.
2. As I do not know internals of the EC firmware, even if today the other
   thermistor channels ordering is seemingly not relevant, we cannot be
   sure it will not change with EC firmware upgrade.

I have reconstructed the order of channels by comparing i2c data dumps
and real-time temps on Windows, eg. sys_therm0 is sent to EC under id 0x02
and represents the TZ71 (around dram on XPS). There is no other reason to
have the names of the channels in this driver except for enforcing the
channel mapping, so `sprintf("sys_therm%d\n", i)` wouldn't be useful.

By allowing source and sink to define the names and not enforcing it in
schema we lose ability to force the correct order, there is no way of
knowing whether "lpddr5-therm" or "ssd-therm" goes first. By forcing
"sys_thermX" convention, one would need to figure which one is which,
for example by referring to laptop schematics. I assume, "thena"'s
schematics has thermistors labeled as "sys_thermX"?

I do agree that labels of the ADC nodes could be more useful for the
user. So far I followed the example of sc8280xp platforms that define
ADC channels with "sys_thermX". Perhaps, we could separate the
io-channel-names and ADC node labels then? eg:

+ io-channel-names = "sys_therm0",
+ 		     "sys_therm1",
...

+ &pmk8550_vadc {
+	sys_therm0: channel@14c {
+ 		reg = <PM8350_ADC7_GPIO3_100K_PU(1)>;
+ 		qcom,hw-settle-time = <200>;
+ 		qcom,ratiometric;
+ 		label = "lpddr5x-therm";

Though not sure if such approach is 'legal'?

Alex

>
> > +
> > +struct dell_xps_ec {
> > +	struct device *dev;
> > +	struct i2c_client *client;
> > +	struct iio_channel *therm_channels[ARRAY_SIZE(dell_xps_ec_therms)];
> > +	struct delayed_work temp_work;
> > +};
> > +
> > +static int dell_xps_ec_suspend_cmd(struct dell_xps_ec *ec, bool suspend)
> > +{
> > +	u8 buf[DELL_XPS_EC_SUSPEND_MSG_LEN] = {};
> > +	int ret;
> > +
> > +	buf[0] = DELL_XPS_EC_SUSPEND_CMD;
> > +	buf[1] = suspend ? 0x01 : 0x00;
> > +	/* bytes 2..63 remain zero */
> > +
> > +	ret = i2c_master_send(ec->client, buf, sizeof(buf));
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +
> > +static int dell_xps_ec_send_temp(struct dell_xps_ec *ec, u8 cmd_byte,
> > +				 int milli_celsius)
> > +{
> > +	u8 buf[DELL_XPS_EC_TEMP_MSG_LEN];
> > +	u16 deci_celsius;
> > +	int ret;
> > +
> > +	/* Convert milli-Celsius to deci-Celsius (Celsius * 10) */
> > +	deci_celsius = milli_celsius / 100;
> > +
> > +	buf[0] = DELL_XPS_EC_TEMP_CMD0;
> > +	buf[1] = DELL_XPS_EC_TEMP_CMD1;
> > +	buf[2] = cmd_byte;
> > +	buf[3] = DELL_XPS_EC_TEMP_CMD3;
> > +	put_unaligned_le16(deci_celsius, &buf[4]);
> > +
> > +	ret = i2c_master_send(ec->client, buf, sizeof(buf));
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +
> > +static void dell_xps_ec_temp_work_fn(struct work_struct *work)
> > +{
> > +	struct dell_xps_ec *ec = container_of(work, struct dell_xps_ec,
> > +					      temp_work.work);
> > +	int val, ret, i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(dell_xps_ec_therms); i++) {
> > +		if (!ec->therm_channels[i])
> > +			continue;
> > +
> > +		ret = iio_read_channel_processed(ec->therm_channels[i], &val);
> > +		if (ret < 0) {
> > +			dev_err_ratelimited(ec->dev,
> > +					    "Failed to read thermistor %s: %d\n",
> > +					    dell_xps_ec_therms[i].name, ret);
> > +			continue;
> > +		}
> > +
> > +		ret = dell_xps_ec_send_temp(ec, dell_xps_ec_therms[i].cmd, val);
> > +		if (ret < 0) {
> > +			dev_err_ratelimited(ec->dev,
> > +					    "Failed to send temp for %s: %d\n",
> > +					    dell_xps_ec_therms[i].name, ret);
> > +		}
> > +	}
> > +
> > +	schedule_delayed_work(&ec->temp_work, DELL_XPS_EC_TEMP_POLL_JIFFIES);
> > +}
> > +
> > +static irqreturn_t dell_xps_ec_irq_handler(int irq, void *data)
> > +{
> > +	struct dell_xps_ec *ec = data;
> > +
> > +	/*
> > +	 * TODO: IRQ is fired on lid-close. Follow Windows example to read out
> > +	 *       the thermistor thresholds and potentially fan speeds.
> > +	 */
> > +	dev_info_ratelimited(ec->dev, "IRQ triggered! (irq=%d)\n", irq);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static int dell_xps_ec_probe(struct i2c_client *client)
> > +{
> > +	struct device *dev = &client->dev;
> > +	struct dell_xps_ec *ec;
> > +	int ret, i;
> > +
> > +	ec = devm_kzalloc(dev, sizeof(*ec), GFP_KERNEL);
> > +	if (!ec)
> > +		return -ENOMEM;
> > +
> > +	ec->dev = dev;
> > +	ec->client = client;
> > +	i2c_set_clientdata(client, ec);
> > +
> > +	/* Set default thermistor profile */
> > +	ret = i2c_master_send(client, dell_xps_ec_thermistor_profile,
> > +			      sizeof(dell_xps_ec_thermistor_profile));
> > +	if (ret < 0)
> > +		return dev_err_probe(dev, ret, "Failed to set thermistor profile\n");
> > +
> > +	/* Get IIO channels for thermistors */
> > +	for (i = 0; i < ARRAY_SIZE(dell_xps_ec_therms); i++) {
> > +		ec->therm_channels[i] =
> > +			devm_iio_channel_get(dev, dell_xps_ec_therms[i].name);
> > +		if (IS_ERR(ec->therm_channels[i])) {
> > +			ret = PTR_ERR(ec->therm_channels[i]);
> > +			ec->therm_channels[i] = NULL;
> > +			if (ret == -EPROBE_DEFER)
> > +				return ret;
> > +			dev_warn(dev, "Thermistor %s not available: %d\n",
> > +				 dell_xps_ec_therms[i].name, ret);
> > +		}
> > +	}
> > +
> > +	/* Start periodic temperature reporting */
> > +	ret = devm_delayed_work_autocancel(dev, &ec->temp_work,
> > +					   dell_xps_ec_temp_work_fn);
> > +	if (ret)
> > +		return ret;
> \n
> > +	schedule_delayed_work(&ec->temp_work, DELL_XPS_EC_TEMP_POLL_JIFFIES);
> > +	dev_dbg(dev, "Started periodic temperature reporting to EC every %d ms\n",
> > +		jiffies_to_msecs(DELL_XPS_EC_TEMP_POLL_JIFFIES));
> > +
> > +	/* Request IRQ for EC events */
> > +	ret = devm_request_threaded_irq(dev, client->irq, NULL,
> > +					dell_xps_ec_irq_handler,
> > +					IRQF_ONESHOT, dev_name(dev), ec);
> > +	if (ret < 0)
> > +		return dev_err_probe(dev, ret, "Failed to request IRQ\n");
> > +
> > +	return 0;
> > +}
> > +
> > +/*
> > + * Notify EC of suspend
> > + *
> > + * This will:
> > + * - Cut power to display/trackpad/keyboard/touchrow, wake-up source still works
> > + */
> > +static int dell_xps_ec_suspend(struct device *dev)
> > +{
> > +	struct dell_xps_ec *ec = dev_get_drvdata(dev);
> > +
> > +	cancel_delayed_work_sync(&ec->temp_work);
> > +
> > +	return dell_xps_ec_suspend_cmd(ec, true);
> > +}
> > +
> > +/*
> > + * Notify EC of resume
> > + *
> > + * This will undo the suspend actions
> > + * Without the resume signal, device would wake up but be forced back into
> > + * suspend by EC within seconds
> > + */
> > +static int dell_xps_ec_resume(struct device *dev)
> > +{
> > +	struct dell_xps_ec *ec = dev_get_drvdata(dev);
> > +	int ret;
> > +
> > +	ret = dell_xps_ec_suspend_cmd(ec, false);
> > +	if (ret)
> > +		return ret;
> > +
> > +	schedule_delayed_work(&ec->temp_work, DELL_XPS_EC_TEMP_POLL_JIFFIES);
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id dell_xps_ec_of_match[] = {
> > +	{ .compatible = "dell,xps13-9345-ec" },
> > +	{}
> > +};
> > +MODULE_DEVICE_TABLE(of, dell_xps_ec_of_match);
> > +
> > +static const struct i2c_device_id dell_xps_ec_i2c_id[] = {
> > +	{ "dell-xps-ec" },
> > +	{}
> > +};
> > +MODULE_DEVICE_TABLE(i2c, dell_xps_ec_i2c_id);
> > +
> > +static const struct dev_pm_ops dell_xps_ec_pm_ops = {
> > +	SYSTEM_SLEEP_PM_OPS(dell_xps_ec_suspend, dell_xps_ec_resume)
> > +};
> > +
> > +static struct i2c_driver dell_xps_ec_driver = {
> > +	.driver = {
> > +		.name = "dell-xps-ec",
> > +		.of_match_table = dell_xps_ec_of_match,
> > +		.pm = &dell_xps_ec_pm_ops,
> > +	},
> > +	.probe = dell_xps_ec_probe,
> > +	.id_table = dell_xps_ec_i2c_id,
> > +};
> > +module_i2c_driver(dell_xps_ec_driver);
> > +
> > +MODULE_AUTHOR("Aleksandrs Vinarskis <alex@xxxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("Dell XPS 13 9345 Embedded Controller");
> > +MODULE_LICENSE("GPL");
> >
>
>