[PATCH resend 0/3] Input: touchscreen - settings module-param support

[PATCH resend 0/3] Input: touchscreen - settings module-param support

[Hans de Goede]

Hi Dmitry, et al,

This is a resend, because the discussion surrounding this patch-set
seems to have dried up without really coming to any conclusion
(summary of previous discussion below).

Original cover-letter (edited for already merged bugfix):

"""
This series adds support for overriding various silead and
goodix touchscreen related device-properties from the kernel cmdline.
This is a reposting of an earlier version which had the following
cover letter:

On x86/ACPI platforms touchscreens mostly just work without needing any
device/model specific configuration. But in some cases (mostly with Silead
and Goodix touchscreens) it is still necessary to manually specify various
touchscreen-properties on a per model basis.

This is handled by drivers/platform/x86/touchscreen_dmi.c which contains
a large list of per-model touchscreen properties which it attaches to the
(i2c)device before the touchscreen driver's probe() method gets called.
This means that ATM changing these settings requires recompiling the
kernel. This makes figuring out what settings/properties a specific
touchscreen needs very hard for normal users to do.

This new settings parameter support is especially useful for helping
users to get their Silead touchscreens to work. These need to have
all of their settings (min-x, width, min-y, height, swapping, inverting)
hardcoded in touchscreen_dmi.c. The settings mod-param allows users
to find the right setting without them needing to be capable of
building their own kernel (and without a lot of rebooting) after which
they can ask someone with some kernel-dev experience to turn this into
a touchscreen_dmi.c patch for them (and yes the way this hw works sucks,
but we cannot change that).

An example of a user who was stuck getting their touchscreen to work and
who was helped by providing a kernel with the settings mod-param added:
https://github.com/onitake/gsl-firmware/discussions/193
"""

Dmitry, you replied to the first patch of this series with:

"""
I totally understand the motivation for this, but I do not think that
having special handling for only touchscreen properties is the right
thing to do. I would very much prefer is we had a more generic approach
of adding/overriding properties (via an swnode?).
"""

To which I wrote the following long reply:

"""
I understand where you are coming from, but I suspect the devicetree
folks are going to not like any generic solution for 2 reasons:

1. Allowing overriding devicetree properties like regulator voltage is a bad idea,
granted users can already do this with a custom DTB, but that is a higher
threshold to pass for a user then just adding something on the kernel cmdline

2. Devicetree supports devicetree-overlays and I expect the devicetree folks
to steer people who want to override random devicetree  properties in that
direction (or in the direction of using a custom DTB)

So the ACPI/x86 case really is somewhat special here and especially the
silead touchscreens are special here. Normally all the settings we are
talking here come from ACPI tables (or can directly be read from the
touchscreen controller) and then messing with these settings would be
a case of using an initrd with a custom ACPI DSDT, just like how
on devicetree I think we would expect people to use a custom DTB and
or a devicetree overlay.

but because of this info lacking from the ACPI tables we have it
hardcoded per 2-in-1/tablet model in:
drivers/platform/x86/touchscreen_dmi.c

The downside of this hardcoding is that testing new settings requires
building a custom kernel, which is both not helpful for having
a quick change settings -> test -> adjust settings cycle when trying
to find the right settings for a new model as well as quite a steep
hill to climb for novice users who want to get things to work on
a new model.

So I do believe that because of this the touchscreen properties
or special in this case and a somewhat custom solution to allow
setting just the touchscreen properties from the cmdline thus
is justified.

Also:

1. Having a mechanism specific to touchscreen properties is
simpler (more KISS) then having to come up with some more
complicated generic property override mechanism.

2. A touchscreen property specific mechanism is much less
susceptible to being misused. Setting the touchscreen properties
wrong cannot really result in any harm. OTOH setting the
max / end-of charging voltage of a lipo cell to 4.6 volt
(this is a real world example) is very much harmful.

The lipo-cell max charge voltage is something which we
in the sysfs interface deliberately disallow to be set any higher
then the boot-time value (lower is allowed). Adding a generic
cmdline mechanism for setting properties would allow
overriding this.
"""
 
And then the discussion stopped.

Regards,

Hans


Hans de Goede (3):
  Input: touchscreen - Extend touchscreen_parse_properties() to allow
    overriding settings with a module option
  Input: silead - Add a settings module-parameter
  Input: goodix - Add a settings module-parameter

 drivers/input/touchscreen.c        | 103 ++++++++++++++++++++++++++---
 drivers/input/touchscreen/goodix.c |   7 +-
 drivers/input/touchscreen/silead.c |  26 +++++---
 include/linux/input/touchscreen.h  |  19 +++++-
 4 files changed, 131 insertions(+), 24 deletions(-)

-- 
2.39.0

[PATCH resend 1/3] Input: touchscreen - Extend touchscreen_parse_properties() to allow overriding settings with a module option

[Hans de Goede]

On x86/ACPI platforms touchscreens mostly just work without needing any
device/model specific configuration. But in some cases (mostly with Silead
and Goodix touchscreens) it is still necessary to manually specify various
touchscreen-properties on a per model basis.

This is handled by drivers/platform/x86/touchscreen_dmi.c which contains
a large list of per-model touchscreen properties which it attaches to the
(i2c)device before the touchscreen driver's probe() method gets called.
This means that ATM changing these settings requires recompiling the
kernel. This makes figuring out what settings/properties a specific
touchscreen needs very hard for normal users to do.

Add a new, optional, settings_override string argument to
touchscreen_parse_properties(), which takes a list of ; separated
property-name=value pairs, e.g. :
"touchscreen-size-x=1665;touchscreen-size-y=1140;touchscreen-swapped-x-y".

This new argument can be used by drivers to implement a module option which
allows users to easily specify alternative settings for testing.

The 2 new touchscreen_property_read_u32() and
touchscreen_property_read_bool() helpers are also exported so that
drivers can use these to add settings-override support to the code
for driver-specific properties.

Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v2:
- Instead of patching all drivers rename touchscreen_parse_properties()
  to touchscreen_parse_properties_with_override() and add
  a static inline wrapper which passes NULL.
---
 drivers/input/touchscreen.c       | 103 ++++++++++++++++++++++++++----
 include/linux/input/touchscreen.h |  19 +++++-
 2 files changed, 109 insertions(+), 13 deletions(-)

diff --git a/drivers/input/touchscreen.c b/drivers/input/touchscreen.c
index 4620e20d0190..3b9505d5468d 100644
--- a/drivers/input/touchscreen.c
+++ b/drivers/input/touchscreen.c
@@ -12,15 +12,80 @@
 #include <linux/input/touchscreen.h>
 #include <linux/module.h>
 
+static int touchscreen_get_prop_from_settings_string(const char *settings,
+						     const char *propname,
+						     bool is_boolean,
+						     u32 *val_ret)
+{
+	char *begin, *end;
+	u32 val;
+
+	if (!settings)
+		return -ENOENT;
+
+	begin = strstr(settings, propname);
+	if (!begin)
+		return -ENOENT;
+
+	/* begin must be either the begin of settings, or be preceded by a ';' */
+	if (begin != settings && begin[-1] != ';')
+		return -EINVAL;
+
+	end = begin + strlen(propname);
+	if (*end != '=') {
+		if (is_boolean && (*end == '\0' || *end == ';')) {
+			*val_ret = true;
+			return 0;
+		}
+		return -EINVAL;
+	}
+
+	val = simple_strtoul(end + 1, &end, 0);
+	if (*end != '\0' && *end != ';')
+		return -EINVAL;
+
+	*val_ret = val;
+	return 0;
+}
+
+int touchscreen_property_read_u32(struct device *dev, const char *propname,
+				  const char *settings, u32 *val)
+{
+	int error;
+
+	error = device_property_read_u32(dev, propname, val);
+
+	if (touchscreen_get_prop_from_settings_string(settings, propname,
+						      false, val) == 0)
+		error = 0;
+
+	return error;
+}
+EXPORT_SYMBOL(touchscreen_property_read_u32);
+
+bool touchscreen_property_read_bool(struct device *dev, const char *propname,
+				    const char *settings)
+{
+	u32 val;
+
+	val = device_property_read_bool(dev, propname);
+
+	touchscreen_get_prop_from_settings_string(settings, propname, true, &val);
+
+	return val;
+}
+EXPORT_SYMBOL(touchscreen_property_read_bool);
+
 static bool touchscreen_get_prop_u32(struct device *dev,
 				     const char *property,
+				     const char *settings,
 				     unsigned int default_value,
 				     unsigned int *value)
 {
 	u32 val;
 	int error;
 
-	error = device_property_read_u32(dev, property, &val);
+	error = touchscreen_property_read_u32(dev, property, settings, &val);
 	if (error) {
 		*value = default_value;
 		return false;
@@ -50,20 +115,28 @@ static void touchscreen_set_params(struct input_dev *dev,
 }
 
 /**
- * touchscreen_parse_properties - parse common touchscreen properties
+ * touchscreen_parse_properties_with_settings - parse common touchscreen properties
  * @input: input device that should be parsed
  * @multitouch: specifies whether parsed properties should be applied to
  *	single-touch or multi-touch axes
  * @prop: pointer to a struct touchscreen_properties into which to store
  *	axis swap and invert info for use with touchscreen_report_x_y();
  *	or %NULL
+ * @settings: string with ; separated name=value pairs overriding
+ *	the device-properties or %NULL.
  *
  * This function parses common properties for touchscreens and sets up the
  * input device accordingly. The function keeps previously set up default
  * values if no value is specified.
+ *
+ * Callers can optional specify a settings string overriding the
+ * device-properties, this can be used to implement a module option which
+ * allows users to easily specify alternative settings for testing.
  */
-void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
-				  struct touchscreen_properties *prop)
+void touchscreen_parse_properties_with_settings(struct input_dev *input,
+						bool multitouch,
+						struct touchscreen_properties *prop,
+						const char *settings)
 {
 	struct device *dev = input->dev.parent;
 	struct input_absinfo *absinfo;
@@ -79,26 +152,32 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
 	axis_y = multitouch ? ABS_MT_POSITION_Y : ABS_Y;
 
 	data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-x",
+						settings,
 						input_abs_get_min(input, axis_x),
 						&minimum);
 	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-x",
+						 settings,
 						 input_abs_get_max(input,
 								   axis_x) + 1,
 						 &maximum);
 	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-x",
+						 settings,
 						 input_abs_get_fuzz(input, axis_x),
 						 &fuzz);
 	if (data_present)
 		touchscreen_set_params(input, axis_x, minimum, maximum - 1, fuzz);
 
 	data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-y",
+						settings,
 						input_abs_get_min(input, axis_y),
 						&minimum);
 	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-y",
+						 settings,
 						 input_abs_get_max(input,
 								   axis_y) + 1,
 						 &maximum);
 	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-y",
+						 settings,
 						 input_abs_get_fuzz(input, axis_y),
 						 &fuzz);
 	if (data_present)
@@ -107,10 +186,12 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
 	axis = multitouch ? ABS_MT_PRESSURE : ABS_PRESSURE;
 	data_present = touchscreen_get_prop_u32(dev,
 						"touchscreen-max-pressure",
+						settings,
 						input_abs_get_max(input, axis),
 						&maximum);
 	data_present |= touchscreen_get_prop_u32(dev,
 						 "touchscreen-fuzz-pressure",
+						 settings,
 						 input_abs_get_fuzz(input, axis),
 						 &fuzz);
 	if (data_present)
@@ -122,28 +203,28 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
 	prop->max_x = input_abs_get_max(input, axis_x);
 	prop->max_y = input_abs_get_max(input, axis_y);
 
-	prop->invert_x =
-		device_property_read_bool(dev, "touchscreen-inverted-x");
+	prop->invert_x = touchscreen_property_read_bool(dev, "touchscreen-inverted-x",
+							settings);
 	if (prop->invert_x) {
 		absinfo = &input->absinfo[axis_x];
 		absinfo->maximum -= absinfo->minimum;
 		absinfo->minimum = 0;
 	}
 
-	prop->invert_y =
-		device_property_read_bool(dev, "touchscreen-inverted-y");
+	prop->invert_y = touchscreen_property_read_bool(dev, "touchscreen-inverted-y",
+							settings);
 	if (prop->invert_y) {
 		absinfo = &input->absinfo[axis_y];
 		absinfo->maximum -= absinfo->minimum;
 		absinfo->minimum = 0;
 	}
 
-	prop->swap_x_y =
-		device_property_read_bool(dev, "touchscreen-swapped-x-y");
+	prop->swap_x_y = touchscreen_property_read_bool(dev, "touchscreen-swapped-x-y",
+							settings);
 	if (prop->swap_x_y)
 		swap(input->absinfo[axis_x], input->absinfo[axis_y]);
 }
-EXPORT_SYMBOL(touchscreen_parse_properties);
+EXPORT_SYMBOL(touchscreen_parse_properties_with_settings);
 
 static void
 touchscreen_apply_prop_to_x_y(const struct touchscreen_properties *prop,
diff --git a/include/linux/input/touchscreen.h b/include/linux/input/touchscreen.h
index fe66e2b58f62..0023c6e368ba 100644
--- a/include/linux/input/touchscreen.h
+++ b/include/linux/input/touchscreen.h
@@ -17,8 +17,23 @@ struct touchscreen_properties {
 	bool swap_x_y;
 };
 
-void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
-				  struct touchscreen_properties *prop);
+void touchscreen_parse_properties_with_settings(struct input_dev *input,
+						bool multitouch,
+						struct touchscreen_properties *prop,
+						const char *settings);
+
+static inline void touchscreen_parse_properties(struct input_dev *input,
+						bool multitouch,
+						struct touchscreen_properties *prop)
+{
+	touchscreen_parse_properties_with_settings(input, multitouch, prop, NULL);
+}
+
+int touchscreen_property_read_u32(struct device *dev, const char *propname,
+				  const char *settings, u32 *val);
+
+bool touchscreen_property_read_bool(struct device *dev, const char *propname,
+				    const char *settings);
 
 void touchscreen_set_mt_pos(struct input_mt_pos *pos,
 			    const struct touchscreen_properties *prop,
-- 
2.39.0

[PATCH resend 2/3] Input: silead - Add a settings module-parameter

[Hans de Goede]

Add a settings module-parameter which can be allowed to specify/override
various device-properties.

Unlike most other touchscreen controllers Silead touchscreens don't tell us
the ranges of the reported x and y coordinates and Silead touchscreens also
often need to have their axis inverted and/or swapped to match the display
coordinates.

Being able to specify the necessary properties through a module parameter,
allows users of new device-models to help us with bringing up support for
new devices without them needing to do a local kernel-build just to modify
these settings.

Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/input/touchscreen/silead.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/input/touchscreen/silead.c b/drivers/input/touchscreen/silead.c
index 8a7351c4414c..22cee8d1bb22 100644
--- a/drivers/input/touchscreen/silead.c
+++ b/drivers/input/touchscreen/silead.c
@@ -58,6 +58,10 @@
 
 #define SILEAD_MAX_FINGERS	10
 
+static char *settings;
+module_param(settings, charp, 0444);
+MODULE_PARM_DESC(settings, "Override touchscreen settings using a ; separated key=value list, e.g. \"touchscreen-size-x=1665;touchscreen-size-y=1140;touchscreen-swapped-x-y\"");
+
 enum silead_ts_power {
 	SILEAD_POWER_ON  = 1,
 	SILEAD_POWER_OFF = 0
@@ -133,14 +137,15 @@ static int silead_ts_request_input_dev(struct silead_ts_data *data)
 
 	input_set_abs_params(data->input, ABS_MT_POSITION_X, 0, 4095, 0, 0);
 	input_set_abs_params(data->input, ABS_MT_POSITION_Y, 0, 4095, 0, 0);
-	touchscreen_parse_properties(data->input, true, &data->prop);
+	touchscreen_parse_properties_with_settings(data->input, true,
+						   &data->prop, settings);
 	silead_apply_efi_fw_min_max(data);
 
 	input_mt_init_slots(data->input, data->max_fingers,
 			    INPUT_MT_DIRECT | INPUT_MT_DROP_UNUSED |
 			    INPUT_MT_TRACK);
 
-	if (device_property_read_bool(dev, "silead,home-button"))
+	if (touchscreen_property_read_bool(dev, "silead,home-button", settings))
 		input_set_capability(data->input, EV_KEY, KEY_LEFTMETA);
 
 	data->input->name = SILEAD_TS_NAME;
@@ -173,7 +178,8 @@ static int silead_ts_request_pen_input_dev(struct silead_ts_data *data)
 	input_set_capability(data->pen_input, EV_KEY, BTN_TOUCH);
 	input_set_capability(data->pen_input, EV_KEY, BTN_TOOL_PEN);
 	set_bit(INPUT_PROP_DIRECT, data->pen_input->propbit);
-	touchscreen_parse_properties(data->pen_input, false, &data->prop);
+	touchscreen_parse_properties_with_settings(data->pen_input, false,
+						   &data->prop, settings);
 	input_abs_set_res(data->pen_input, ABS_X, data->pen_x_res);
 	input_abs_set_res(data->pen_input, ABS_Y, data->pen_y_res);
 
@@ -523,8 +529,8 @@ static int silead_ts_setup(struct i2c_client *client)
 	 * this.
 	 */
 
-	if (device_property_read_bool(&client->dev,
-				      "silead,stuck-controller-bug")) {
+	if (touchscreen_property_read_bool(&client->dev, "silead,stuck-controller-bug",
+					   settings)) {
 		pm_runtime_set_active(&client->dev);
 		pm_runtime_enable(&client->dev);
 		pm_runtime_allow(&client->dev);
@@ -591,8 +597,8 @@ static void silead_ts_read_props(struct i2c_client *client)
 	const char *str;
 	int error;
 
-	error = device_property_read_u32(dev, "silead,max-fingers",
-					 &data->max_fingers);
+	error = touchscreen_property_read_u32(dev, "silead,max-fingers", settings,
+					      &data->max_fingers);
 	if (error) {
 		dev_dbg(dev, "Max fingers read error %d\n", error);
 		data->max_fingers = 5; /* Most devices handle up-to 5 fingers */
@@ -605,9 +611,9 @@ static void silead_ts_read_props(struct i2c_client *client)
 	else
 		dev_dbg(dev, "Firmware file name read error. Using default.");
 
-	data->pen_supported = device_property_read_bool(dev, "silead,pen-supported");
-	device_property_read_u32(dev, "silead,pen-resolution-x", &data->pen_x_res);
-	device_property_read_u32(dev, "silead,pen-resolution-y", &data->pen_y_res);
+	data->pen_supported = touchscreen_property_read_bool(dev, "silead,pen-supported", settings);
+	touchscreen_property_read_u32(dev, "silead,pen-resolution-x", settings, &data->pen_x_res);
+	touchscreen_property_read_u32(dev, "silead,pen-resolution-y", settings, &data->pen_y_res);
 }
 
 #ifdef CONFIG_ACPI
-- 
2.39.0

[PATCH resend 3/3] Input: goodix - Add a settings module-parameter

[Hans de Goede]

Add a settings module-parameter which can be allowed to specify/override
various device-properties.

Usuually Goodix touchscreens on x86 devices (where there is no devicetree
to specify the properties) just work. But in some cases the touchscreen is
mounted 90 or 180 degrees rotated vs the display, requiring setting the
touchscreen-x/y-inverted or touchscreen-swapped-x-y properties.

Being able to specify the necessary properties through a module parameter,
allows users of new device-models to help us with bringing up support for
new devices without them needing to do a local kernel-build just to modify
these settings.

Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/input/touchscreen/goodix.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
index 620f5ec0962f..a105dee04156 100644
--- a/drivers/input/touchscreen/goodix.c
+++ b/drivers/input/touchscreen/goodix.c
@@ -53,6 +53,10 @@
 #define ACPI_GPIO_SUPPORT
 #endif
 
+static char *settings;
+module_param(settings, charp, 0444);
+MODULE_PARM_DESC(settings, "Override touchscreen settings using a ; separated key=value list, e.g. \"touchscreen-fuzz-x=5;touchscreen-fuzz-y=5;touchscreen-swapped-x-y\"");
+
 struct goodix_chip_id {
 	const char *id;
 	const struct goodix_chip_data *data;
@@ -1197,7 +1201,8 @@ static int goodix_configure_dev(struct goodix_ts_data *ts)
 	goodix_read_config(ts);
 
 	/* Try overriding touchscreen parameters via device properties */
-	touchscreen_parse_properties(ts->input_dev, true, &ts->prop);
+	touchscreen_parse_properties_with_settings(ts->input_dev, true,
+						   &ts->prop, settings);
 
 	if (!ts->prop.max_x || !ts->prop.max_y || !ts->max_touch_num) {
 		if (!ts->reset_controller_at_probe &&
-- 
2.39.0

Re: [PATCH resend 1/3] Input: touchscreen - Extend touchscreen_parse_properties() to allow overriding settings with a module option

[Jeff LaBundy]

Hi Hans,

On Wed, Jan 25, 2023 at 11:54:14AM +0100, Hans de Goede wrote:
> On x86/ACPI platforms touchscreens mostly just work without needing any
> device/model specific configuration. But in some cases (mostly with Silead
> and Goodix touchscreens) it is still necessary to manually specify various
> touchscreen-properties on a per model basis.
> 
> This is handled by drivers/platform/x86/touchscreen_dmi.c which contains
> a large list of per-model touchscreen properties which it attaches to the
> (i2c)device before the touchscreen driver's probe() method gets called.
> This means that ATM changing these settings requires recompiling the
> kernel. This makes figuring out what settings/properties a specific
> touchscreen needs very hard for normal users to do.
> 
> Add a new, optional, settings_override string argument to
> touchscreen_parse_properties(), which takes a list of ; separated
> property-name=value pairs, e.g. :
> "touchscreen-size-x=1665;touchscreen-size-y=1140;touchscreen-swapped-x-y".
> 
> This new argument can be used by drivers to implement a module option which
> allows users to easily specify alternative settings for testing.
> 
> The 2 new touchscreen_property_read_u32() and
> touchscreen_property_read_bool() helpers are also exported so that
> drivers can use these to add settings-override support to the code
> for driver-specific properties.
> 
> Reviewed-by: Bastien Nocera <hadess@hadess.net>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---

Thank you for resurrecting this series. Perhaps I can give my own $.02 as
a fellow customer of input.

I can appreciate the hesitancy that was expressed in the past, as this is
not a generic solution and is specific to touch devices. However, I also
agree with your point that extending dts overrides to all properties opens
a can of worms which should not necessarily gate this benign series (i.e.,
"good is not the enemy of great").

Personally I am highly in favor of this series because I myself have had
to support this very situation where a panel arrives 180 degrees from the
expected orientation, and fellow teammates who are not in a position to
quickly spin a build need a means to quickly unblock themselves through a
serial console or other means.

The code itself also LGTM and I verified there were no regressions on one
of my own drivers that expects these properties to come from dts, and so:

Reviewed-by: Jeff LaBundy <jeff@labundy.com>

> Changes in v2:
> - Instead of patching all drivers rename touchscreen_parse_properties()
>   to touchscreen_parse_properties_with_override() and add
>   a static inline wrapper which passes NULL.
> ---
>  drivers/input/touchscreen.c       | 103 ++++++++++++++++++++++++++----
>  include/linux/input/touchscreen.h |  19 +++++-
>  2 files changed, 109 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/input/touchscreen.c b/drivers/input/touchscreen.c
> index 4620e20d0190..3b9505d5468d 100644
> --- a/drivers/input/touchscreen.c
> +++ b/drivers/input/touchscreen.c
> @@ -12,15 +12,80 @@
>  #include <linux/input/touchscreen.h>
>  #include <linux/module.h>
>  
> +static int touchscreen_get_prop_from_settings_string(const char *settings,
> +						     const char *propname,
> +						     bool is_boolean,
> +						     u32 *val_ret)
> +{
> +	char *begin, *end;
> +	u32 val;
> +
> +	if (!settings)
> +		return -ENOENT;
> +
> +	begin = strstr(settings, propname);
> +	if (!begin)
> +		return -ENOENT;
> +
> +	/* begin must be either the begin of settings, or be preceded by a ';' */
> +	if (begin != settings && begin[-1] != ';')
> +		return -EINVAL;
> +
> +	end = begin + strlen(propname);
> +	if (*end != '=') {
> +		if (is_boolean && (*end == '\0' || *end == ';')) {
> +			*val_ret = true;
> +			return 0;
> +		}
> +		return -EINVAL;
> +	}
> +
> +	val = simple_strtoul(end + 1, &end, 0);
> +	if (*end != '\0' && *end != ';')
> +		return -EINVAL;
> +
> +	*val_ret = val;
> +	return 0;
> +}
> +
> +int touchscreen_property_read_u32(struct device *dev, const char *propname,
> +				  const char *settings, u32 *val)
> +{
> +	int error;
> +
> +	error = device_property_read_u32(dev, propname, val);
> +
> +	if (touchscreen_get_prop_from_settings_string(settings, propname,
> +						      false, val) == 0)
> +		error = 0;
> +
> +	return error;
> +}
> +EXPORT_SYMBOL(touchscreen_property_read_u32);
> +
> +bool touchscreen_property_read_bool(struct device *dev, const char *propname,
> +				    const char *settings)
> +{
> +	u32 val;
> +
> +	val = device_property_read_bool(dev, propname);
> +
> +	touchscreen_get_prop_from_settings_string(settings, propname, true, &val);
> +
> +	return val;
> +}
> +EXPORT_SYMBOL(touchscreen_property_read_bool);
> +
>  static bool touchscreen_get_prop_u32(struct device *dev,
>  				     const char *property,
> +				     const char *settings,
>  				     unsigned int default_value,
>  				     unsigned int *value)
>  {
>  	u32 val;
>  	int error;
>  
> -	error = device_property_read_u32(dev, property, &val);
> +	error = touchscreen_property_read_u32(dev, property, settings, &val);
>  	if (error) {
>  		*value = default_value;
>  		return false;
> @@ -50,20 +115,28 @@ static void touchscreen_set_params(struct input_dev *dev,
>  }
>  
>  /**
> - * touchscreen_parse_properties - parse common touchscreen properties
> + * touchscreen_parse_properties_with_settings - parse common touchscreen properties
>   * @input: input device that should be parsed
>   * @multitouch: specifies whether parsed properties should be applied to
>   *	single-touch or multi-touch axes
>   * @prop: pointer to a struct touchscreen_properties into which to store
>   *	axis swap and invert info for use with touchscreen_report_x_y();
>   *	or %NULL
> + * @settings: string with ; separated name=value pairs overriding
> + *	the device-properties or %NULL.
>   *
>   * This function parses common properties for touchscreens and sets up the
>   * input device accordingly. The function keeps previously set up default
>   * values if no value is specified.
> + *
> + * Callers can optional specify a settings string overriding the
> + * device-properties, this can be used to implement a module option which
> + * allows users to easily specify alternative settings for testing.
>   */
> -void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
> -				  struct touchscreen_properties *prop)
> +void touchscreen_parse_properties_with_settings(struct input_dev *input,
> +						bool multitouch,
> +						struct touchscreen_properties *prop,
> +						const char *settings)
>  {
>  	struct device *dev = input->dev.parent;
>  	struct input_absinfo *absinfo;
> @@ -79,26 +152,32 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
>  	axis_y = multitouch ? ABS_MT_POSITION_Y : ABS_Y;
>  
>  	data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-x",
> +						settings,
>  						input_abs_get_min(input, axis_x),
>  						&minimum);
>  	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-x",
> +						 settings,
>  						 input_abs_get_max(input,
>  								   axis_x) + 1,
>  						 &maximum);
>  	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-x",
> +						 settings,
>  						 input_abs_get_fuzz(input, axis_x),
>  						 &fuzz);
>  	if (data_present)
>  		touchscreen_set_params(input, axis_x, minimum, maximum - 1, fuzz);
>  
>  	data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-y",
> +						settings,
>  						input_abs_get_min(input, axis_y),
>  						&minimum);
>  	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-y",
> +						 settings,
>  						 input_abs_get_max(input,
>  								   axis_y) + 1,
>  						 &maximum);
>  	data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-y",
> +						 settings,
>  						 input_abs_get_fuzz(input, axis_y),
>  						 &fuzz);
>  	if (data_present)
> @@ -107,10 +186,12 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
>  	axis = multitouch ? ABS_MT_PRESSURE : ABS_PRESSURE;
>  	data_present = touchscreen_get_prop_u32(dev,
>  						"touchscreen-max-pressure",
> +						settings,
>  						input_abs_get_max(input, axis),
>  						&maximum);
>  	data_present |= touchscreen_get_prop_u32(dev,
>  						 "touchscreen-fuzz-pressure",
> +						 settings,
>  						 input_abs_get_fuzz(input, axis),
>  						 &fuzz);
>  	if (data_present)
> @@ -122,28 +203,28 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
>  	prop->max_x = input_abs_get_max(input, axis_x);
>  	prop->max_y = input_abs_get_max(input, axis_y);
>  
> -	prop->invert_x =
> -		device_property_read_bool(dev, "touchscreen-inverted-x");
> +	prop->invert_x = touchscreen_property_read_bool(dev, "touchscreen-inverted-x",
> +							settings);
>  	if (prop->invert_x) {
>  		absinfo = &input->absinfo[axis_x];
>  		absinfo->maximum -= absinfo->minimum;
>  		absinfo->minimum = 0;
>  	}
>  
> -	prop->invert_y =
> -		device_property_read_bool(dev, "touchscreen-inverted-y");
> +	prop->invert_y = touchscreen_property_read_bool(dev, "touchscreen-inverted-y",
> +							settings);
>  	if (prop->invert_y) {
>  		absinfo = &input->absinfo[axis_y];
>  		absinfo->maximum -= absinfo->minimum;
>  		absinfo->minimum = 0;
>  	}
>  
> -	prop->swap_x_y =
> -		device_property_read_bool(dev, "touchscreen-swapped-x-y");
> +	prop->swap_x_y = touchscreen_property_read_bool(dev, "touchscreen-swapped-x-y",
> +							settings);
>  	if (prop->swap_x_y)
>  		swap(input->absinfo[axis_x], input->absinfo[axis_y]);
>  }
> -EXPORT_SYMBOL(touchscreen_parse_properties);
> +EXPORT_SYMBOL(touchscreen_parse_properties_with_settings);
>  
>  static void
>  touchscreen_apply_prop_to_x_y(const struct touchscreen_properties *prop,
> diff --git a/include/linux/input/touchscreen.h b/include/linux/input/touchscreen.h
> index fe66e2b58f62..0023c6e368ba 100644
> --- a/include/linux/input/touchscreen.h
> +++ b/include/linux/input/touchscreen.h
> @@ -17,8 +17,23 @@ struct touchscreen_properties {
>  	bool swap_x_y;
>  };
>  
> -void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
> -				  struct touchscreen_properties *prop);
> +void touchscreen_parse_properties_with_settings(struct input_dev *input,
> +						bool multitouch,
> +						struct touchscreen_properties *prop,
> +						const char *settings);
> +
> +static inline void touchscreen_parse_properties(struct input_dev *input,
> +						bool multitouch,
> +						struct touchscreen_properties *prop)
> +{
> +	touchscreen_parse_properties_with_settings(input, multitouch, prop, NULL);
> +}
> +
> +int touchscreen_property_read_u32(struct device *dev, const char *propname,
> +				  const char *settings, u32 *val);
> +
> +bool touchscreen_property_read_bool(struct device *dev, const char *propname,
> +				    const char *settings);
>  
>  void touchscreen_set_mt_pos(struct input_mt_pos *pos,
>  			    const struct touchscreen_properties *prop,
> -- 
> 2.39.0
> 

Kind regards,
Jeff LaBundy

Re: [PATCH resend 2/3] Input: silead - Add a settings module-parameter

[Jeff LaBundy]

Hi Hans,

On Wed, Jan 25, 2023 at 11:54:15AM +0100, Hans de Goede wrote:
> Add a settings module-parameter which can be allowed to specify/override
> various device-properties.
> 
> Unlike most other touchscreen controllers Silead touchscreens don't tell us
> the ranges of the reported x and y coordinates and Silead touchscreens also
> often need to have their axis inverted and/or swapped to match the display
> coordinates.
> 
> Being able to specify the necessary properties through a module parameter,
> allows users of new device-models to help us with bringing up support for
> new devices without them needing to do a local kernel-build just to modify
> these settings.
> 
> Reviewed-by: Bastien Nocera <hadess@hadess.net>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

This LGTM, with one comment that I do not feel strongly about.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>

> ---
>  drivers/input/touchscreen/silead.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/silead.c b/drivers/input/touchscreen/silead.c
> index 8a7351c4414c..22cee8d1bb22 100644
> --- a/drivers/input/touchscreen/silead.c
> +++ b/drivers/input/touchscreen/silead.c
> @@ -58,6 +58,10 @@
>  
>  #define SILEAD_MAX_FINGERS	10
>  
> +static char *settings;
> +module_param(settings, charp, 0444);
> +MODULE_PARM_DESC(settings, "Override touchscreen settings using a ; separated key=value list, e.g. \"touchscreen-size-x=1665;touchscreen-size-y=1140;touchscreen-swapped-x-y\"");
> +
>  enum silead_ts_power {
>  	SILEAD_POWER_ON  = 1,
>  	SILEAD_POWER_OFF = 0
> @@ -133,14 +137,15 @@ static int silead_ts_request_input_dev(struct silead_ts_data *data)
>  
>  	input_set_abs_params(data->input, ABS_MT_POSITION_X, 0, 4095, 0, 0);
>  	input_set_abs_params(data->input, ABS_MT_POSITION_Y, 0, 4095, 0, 0);
> -	touchscreen_parse_properties(data->input, true, &data->prop);
> +	touchscreen_parse_properties_with_settings(data->input, true,
> +						   &data->prop, settings);
>  	silead_apply_efi_fw_min_max(data);
>  
>  	input_mt_init_slots(data->input, data->max_fingers,
>  			    INPUT_MT_DIRECT | INPUT_MT_DROP_UNUSED |
>  			    INPUT_MT_TRACK);
>  
> -	if (device_property_read_bool(dev, "silead,home-button"))
> +	if (touchscreen_property_read_bool(dev, "silead,home-button", settings))

While harmless, this seems like a bit of an overuse of the proposed
functionality. Either the platform has a home button or it does not.
Would users really need to experiment with this property enabled or
disabled?

>  		input_set_capability(data->input, EV_KEY, KEY_LEFTMETA);
>  
>  	data->input->name = SILEAD_TS_NAME;
> @@ -173,7 +178,8 @@ static int silead_ts_request_pen_input_dev(struct silead_ts_data *data)
>  	input_set_capability(data->pen_input, EV_KEY, BTN_TOUCH);
>  	input_set_capability(data->pen_input, EV_KEY, BTN_TOOL_PEN);
>  	set_bit(INPUT_PROP_DIRECT, data->pen_input->propbit);
> -	touchscreen_parse_properties(data->pen_input, false, &data->prop);
> +	touchscreen_parse_properties_with_settings(data->pen_input, false,
> +						   &data->prop, settings);
>  	input_abs_set_res(data->pen_input, ABS_X, data->pen_x_res);
>  	input_abs_set_res(data->pen_input, ABS_Y, data->pen_y_res);
>  
> @@ -523,8 +529,8 @@ static int silead_ts_setup(struct i2c_client *client)
>  	 * this.
>  	 */
>  
> -	if (device_property_read_bool(&client->dev,
> -				      "silead,stuck-controller-bug")) {
> +	if (touchscreen_property_read_bool(&client->dev, "silead,stuck-controller-bug",
> +					   settings)) {
>  		pm_runtime_set_active(&client->dev);
>  		pm_runtime_enable(&client->dev);
>  		pm_runtime_allow(&client->dev);
> @@ -591,8 +597,8 @@ static void silead_ts_read_props(struct i2c_client *client)
>  	const char *str;
>  	int error;
>  
> -	error = device_property_read_u32(dev, "silead,max-fingers",
> -					 &data->max_fingers);
> +	error = touchscreen_property_read_u32(dev, "silead,max-fingers", settings,
> +					      &data->max_fingers);
>  	if (error) {
>  		dev_dbg(dev, "Max fingers read error %d\n", error);
>  		data->max_fingers = 5; /* Most devices handle up-to 5 fingers */
> @@ -605,9 +611,9 @@ static void silead_ts_read_props(struct i2c_client *client)
>  	else
>  		dev_dbg(dev, "Firmware file name read error. Using default.");
>  
> -	data->pen_supported = device_property_read_bool(dev, "silead,pen-supported");
> -	device_property_read_u32(dev, "silead,pen-resolution-x", &data->pen_x_res);
> -	device_property_read_u32(dev, "silead,pen-resolution-y", &data->pen_y_res);
> +	data->pen_supported = touchscreen_property_read_bool(dev, "silead,pen-supported", settings);
> +	touchscreen_property_read_u32(dev, "silead,pen-resolution-x", settings, &data->pen_x_res);
> +	touchscreen_property_read_u32(dev, "silead,pen-resolution-y", settings, &data->pen_y_res);
>  }
>  
>  #ifdef CONFIG_ACPI
> -- 
> 2.39.0
> 

Kind regards,
Jeff LaBundy

Re: [PATCH resend 3/3] Input: goodix - Add a settings module-parameter

[Jeff LaBundy]

On Wed, Jan 25, 2023 at 11:54:16AM +0100, Hans de Goede wrote:
> Add a settings module-parameter which can be allowed to specify/override
> various device-properties.
> 
> Usuually Goodix touchscreens on x86 devices (where there is no devicetree
> to specify the properties) just work. But in some cases the touchscreen is
> mounted 90 or 180 degrees rotated vs the display, requiring setting the
> touchscreen-x/y-inverted or touchscreen-swapped-x-y properties.
> 
> Being able to specify the necessary properties through a module parameter,
> allows users of new device-models to help us with bringing up support for
> new devices without them needing to do a local kernel-build just to modify
> these settings.
> 
> Reviewed-by: Bastien Nocera <hadess@hadess.net>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Reviewed-by: Jeff LaBundy <jeff@labundy.com>

> ---
>  drivers/input/touchscreen/goodix.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
> index 620f5ec0962f..a105dee04156 100644
> --- a/drivers/input/touchscreen/goodix.c
> +++ b/drivers/input/touchscreen/goodix.c
> @@ -53,6 +53,10 @@
>  #define ACPI_GPIO_SUPPORT
>  #endif
>  
> +static char *settings;
> +module_param(settings, charp, 0444);
> +MODULE_PARM_DESC(settings, "Override touchscreen settings using a ; separated key=value list, e.g. \"touchscreen-fuzz-x=5;touchscreen-fuzz-y=5;touchscreen-swapped-x-y\"");
> +
>  struct goodix_chip_id {
>  	const char *id;
>  	const struct goodix_chip_data *data;
> @@ -1197,7 +1201,8 @@ static int goodix_configure_dev(struct goodix_ts_data *ts)
>  	goodix_read_config(ts);
>  
>  	/* Try overriding touchscreen parameters via device properties */
> -	touchscreen_parse_properties(ts->input_dev, true, &ts->prop);
> +	touchscreen_parse_properties_with_settings(ts->input_dev, true,
> +						   &ts->prop, settings);
>  
>  	if (!ts->prop.max_x || !ts->prop.max_y || !ts->max_touch_num) {
>  		if (!ts->reset_controller_at_probe &&
> -- 
> 2.39.0
> 

Re: [PATCH resend 2/3] Input: silead - Add a settings module-parameter

[Hans de Goede]

Hi,

On 1/26/23 05:51, Jeff LaBundy wrote:
> Hi Hans,
> 
> On Wed, Jan 25, 2023 at 11:54:15AM +0100, Hans de Goede wrote:
>> Add a settings module-parameter which can be allowed to specify/override
>> various device-properties.
>>
>> Unlike most other touchscreen controllers Silead touchscreens don't tell us
>> the ranges of the reported x and y coordinates and Silead touchscreens also
>> often need to have their axis inverted and/or swapped to match the display
>> coordinates.
>>
>> Being able to specify the necessary properties through a module parameter,
>> allows users of new device-models to help us with bringing up support for
>> new devices without them needing to do a local kernel-build just to modify
>> these settings.
>>
>> Reviewed-by: Bastien Nocera <hadess@hadess.net>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> 
> This LGTM, with one comment that I do not feel strongly about.
> 
> Reviewed-by: Jeff LaBundy <jeff@labundy.com>
> 
>> ---
>>  drivers/input/touchscreen/silead.c | 26 ++++++++++++++++----------
>>  1 file changed, 16 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/input/touchscreen/silead.c b/drivers/input/touchscreen/silead.c
>> index 8a7351c4414c..22cee8d1bb22 100644
>> --- a/drivers/input/touchscreen/silead.c
>> +++ b/drivers/input/touchscreen/silead.c
>> @@ -58,6 +58,10 @@
>>  
>>  #define SILEAD_MAX_FINGERS	10
>>  
>> +static char *settings;
>> +module_param(settings, charp, 0444);
>> +MODULE_PARM_DESC(settings, "Override touchscreen settings using a ; separated key=value list, e.g. \"touchscreen-size-x=1665;touchscreen-size-y=1140;touchscreen-swapped-x-y\"");
>> +
>>  enum silead_ts_power {
>>  	SILEAD_POWER_ON  = 1,
>>  	SILEAD_POWER_OFF = 0
>> @@ -133,14 +137,15 @@ static int silead_ts_request_input_dev(struct silead_ts_data *data)
>>  
>>  	input_set_abs_params(data->input, ABS_MT_POSITION_X, 0, 4095, 0, 0);
>>  	input_set_abs_params(data->input, ABS_MT_POSITION_Y, 0, 4095, 0, 0);
>> -	touchscreen_parse_properties(data->input, true, &data->prop);
>> +	touchscreen_parse_properties_with_settings(data->input, true,
>> +						   &data->prop, settings);
>>  	silead_apply_efi_fw_min_max(data);
>>  
>>  	input_mt_init_slots(data->input, data->max_fingers,
>>  			    INPUT_MT_DIRECT | INPUT_MT_DROP_UNUSED |
>>  			    INPUT_MT_TRACK);
>>  
>> -	if (device_property_read_bool(dev, "silead,home-button"))
>> +	if (touchscreen_property_read_bool(dev, "silead,home-button", settings))
> 
> While harmless, this seems like a bit of an overuse of the proposed
> functionality. Either the platform has a home button or it does not.
> Would users really need to experiment with this property enabled or
> disabled?

Thank you for the review.

Having this is actually useful, because users do need to check if
they actually have a home-button:

1. Always setting this may lead to false-positive home button presses
   on some models (IIRC, this has been around for a long time)

2. The home button typical is a windows logo printed on the front of
   cheap windows tablets below the screen. Recently I was adding info
   for yet another such cheap tablet and I asked the user to test
   the home-button since the windows logo was clearly there visually.
   But on this specific model touching the windows logo does not do
   anything.

Combined these 2 make it useful for users to be able to explicitly
test the home-button functionality.

Regards,

Hans


> 
>>  		input_set_capability(data->input, EV_KEY, KEY_LEFTMETA);
>>  
>>  	data->input->name = SILEAD_TS_NAME;
>> @@ -173,7 +178,8 @@ static int silead_ts_request_pen_input_dev(struct silead_ts_data *data)
>>  	input_set_capability(data->pen_input, EV_KEY, BTN_TOUCH);
>>  	input_set_capability(data->pen_input, EV_KEY, BTN_TOOL_PEN);
>>  	set_bit(INPUT_PROP_DIRECT, data->pen_input->propbit);
>> -	touchscreen_parse_properties(data->pen_input, false, &data->prop);
>> +	touchscreen_parse_properties_with_settings(data->pen_input, false,
>> +						   &data->prop, settings);
>>  	input_abs_set_res(data->pen_input, ABS_X, data->pen_x_res);
>>  	input_abs_set_res(data->pen_input, ABS_Y, data->pen_y_res);
>>  
>> @@ -523,8 +529,8 @@ static int silead_ts_setup(struct i2c_client *client)
>>  	 * this.
>>  	 */
>>  
>> -	if (device_property_read_bool(&client->dev,
>> -				      "silead,stuck-controller-bug")) {
>> +	if (touchscreen_property_read_bool(&client->dev, "silead,stuck-controller-bug",
>> +					   settings)) {
>>  		pm_runtime_set_active(&client->dev);
>>  		pm_runtime_enable(&client->dev);
>>  		pm_runtime_allow(&client->dev);
>> @@ -591,8 +597,8 @@ static void silead_ts_read_props(struct i2c_client *client)
>>  	const char *str;
>>  	int error;
>>  
>> -	error = device_property_read_u32(dev, "silead,max-fingers",
>> -					 &data->max_fingers);
>> +	error = touchscreen_property_read_u32(dev, "silead,max-fingers", settings,
>> +					      &data->max_fingers);
>>  	if (error) {
>>  		dev_dbg(dev, "Max fingers read error %d\n", error);
>>  		data->max_fingers = 5; /* Most devices handle up-to 5 fingers */
>> @@ -605,9 +611,9 @@ static void silead_ts_read_props(struct i2c_client *client)
>>  	else
>>  		dev_dbg(dev, "Firmware file name read error. Using default.");
>>  
>> -	data->pen_supported = device_property_read_bool(dev, "silead,pen-supported");
>> -	device_property_read_u32(dev, "silead,pen-resolution-x", &data->pen_x_res);
>> -	device_property_read_u32(dev, "silead,pen-resolution-y", &data->pen_y_res);
>> +	data->pen_supported = touchscreen_property_read_bool(dev, "silead,pen-supported", settings);
>> +	touchscreen_property_read_u32(dev, "silead,pen-resolution-x", settings, &data->pen_x_res);
>> +	touchscreen_property_read_u32(dev, "silead,pen-resolution-y", settings, &data->pen_y_res);
>>  }
>>  
>>  #ifdef CONFIG_ACPI
>> -- 
>> 2.39.0
>>
> 
> Kind regards,
> Jeff LaBundy
> 

Re: [PATCH resend 2/3] Input: silead - Add a settings module-parameter

[Gregor Riepl]

> Having this is actually useful, because users do need to check if
> they actually have a home-button:
> 
> 1. Always setting this may lead to false-positive home button presses
>     on some models (IIRC, this has been around for a long time)
> 
> 2. The home button typical is a windows logo printed on the front of
>     cheap windows tablets below the screen. Recently I was adding info
>     for yet another such cheap tablet and I asked the user to test
>     the home-button since the windows logo was clearly there visually.
>     But on this specific model touching the windows logo does not do
>     anything.

I vaguely remember that some users also reported Android-targeted 
tablets where the surface covering the soft-touch buttons was simply an 
extension of the whole touch surface, and not send any explicit key 
press events.

But I may be mistaken, or it was a bug in an older driver version that 
didn't support touch buttons well.