Thanks for the feedback. I'll send out a v2 shortly: Alex, can you
please retest when I do to make sure there aren't any regressions? None
of these suggestions affect the core flow of how either of the
workarounds work, so I'm not expecting any that wouldn't also reproduce
on my EC backlight system that doesn't have either of these problems,
but I can send you the updated version off-list first if you prefer.
Detailed replies below:
On 3/15/22 9:50 PM, Barnabás Pőcze wrote:
Hi
The platform-driver-x86 maintainers should've probably been
CCd. You may or may not know, but the `scripts/get_maintainers.pl`
script can be used to determine the appropriate recipients.
Indeed. I've copied the pdx86 maintainers on this message and will for
future correspondence regarding this patch.
2022. március 16., szerda 2:25 keltezéssel, Daniel Dadap írta:
Some notebook systems with EC-driven backlight control appear to have a
firmware bug which causes the system to use GPU-driven backlight control
upon a fresh boot, but then switches to EC-driven backlight control
after completing a suspend/resume cycle. All the while, the firmware
reports that the backlight is under EC control, regardless of what is
actually controlling the backlight brightness.
This leads to the following behavior:
* nvidia-wmi-ec-backlight gets probed on a fresh boot, due to the
WMI-wrapped ACPI method erroneously reporting EC control.
* nvidia-wmi-ec-backlight does not work until after a suspend/resume
cycle, due to the backlight control actually being GPU-driven.
* GPU drivers also register their own backlight handlers: in the case
of the notebook system where this behavior has been observed, both
amdgpu and the NVIDIA proprietary driver register backlight handlers.
* The GPU which has backlight control upon a fresh boot (amdgpu in the
case observed so far) can successfully control the backlight through
its backlight driver's sysfs interface, but stops working after the
first suspend/resume cycle.
* nvidia-wmi-ec-backlight is unable to control the backlight upon a
fresh boot, but begins to work after the first suspend/resume cycle.
* The GPU which does not have backlight control (NVIDIA in this case)
is not able to control the backlight at any point while the system
is in operation. On similar hybrid systems with an EC-controlled
backlight, and AMD/NVIDIA iGPU/dGPU, the NVIDIA proprietary driver
does not register its backlight handler. It has not been determined
whether the non-functional handler registered by the NVIDIA driver
is due to another firmware bug, or a bug in the NVIDIA driver.
Since nvidia-wmi-ec-backlight registers as a BACKLIGHT_FIRMWARE type
device, it takes precedence over the BACKLIGHT_RAW devices registered
by the GPU drivers. This in turn leads to backlight control appearing
to be non-functional until after completing a suspend/resume cycle.
However, it is still possible to control the backlight through direct
interaction with the working GPU driver's backlight sysfs interface.
These systems also appear to have a second firmware bug which resets
the EC's brightness level to 100% on resume, but leaves the state in
the kernel at the pre-suspend level. This causes attempts to save
and restore the backlight level across the suspend/resume cycle to
fail, due to the level appearing not to change even though it did.
In order to work around these issue, add quirk tables to detect
systems that are known to show these behaviors. So far, there is
only one known system that requires these workarounds, and both
issues are present on that system, but the quirks are tracked in
separate tables to make it easier to add them to other systems which
may exhibit one of the bugs, but not the other. The original systems
that this driver was tested on during development do not exhibit
either of these quirks.
If a system with the "GPU driver has backlight control" quirk is
detected, nvidia-wmi-ec-backlight will grab a reference to the working
(when freshly booted) GPU backlight handler and relays any backlight
brightness level change requests directed at the EC to also be applied
to the GPU backlight interface. This leads to redundant updates
directed at the GPU backlight driver after a suspend/resume cycle, but
it does allow the EC backlight control to work when the system is
freshly booted.
If a system with the "backlight level reset to full on resume" quirk
is detected, nvidia-wmi-ec-backlight will register a PM notifier to
reset the backlight to the previous level upon resume.
These workarounds are also plumbed through to kernel module parameters,
to make it easier for users who suspect they may be affected by one or
both of these bugs to test whether these workarounds are effective on
their systems as well.
Signed-off-by: Daniel Dadap <ddadap@xxxxxxxxxx>
Tested-by: Alexandru Dinu <alex.dinu07@xxxxxxxxx>
---
.../platform/x86/nvidia-wmi-ec-backlight.c | 181 +++++++++++++++++-
1 file changed, 179 insertions(+), 2 deletions(-)
diff --git a/drivers/platform/x86/nvidia-wmi-ec-backlight.c b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
index 61e37194df70..ccb3b506c12c 100644
--- a/drivers/platform/x86/nvidia-wmi-ec-backlight.c
+++ b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
@@ -3,8 +3,11 @@
* Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved.
*/
+#define pr_fmt(f) "%s: " f "\n", KBUILD_MODNAME
`KBUILD_MODNAME` is a string literal, so you can do e.g.
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
#include <linux/acpi.h>
#include <linux/backlight.h>
+#include <linux/dmi.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/types.h>
@@ -75,6 +78,69 @@ struct wmi_brightness_args {
u32 ignored[3];
};
+/**
+ * struct nvidia_wmi_ec_backlight_priv - driver private data
+ * @bl_dev: the associated backlight device
+ * @proxy_target: backlight device which receives relayed brightness changes
+ * @notifier: notifier block for resume callback
+ */
+struct nvidia_wmi_ec_backlight_priv {
+ struct backlight_device *bl_dev;
+ struct backlight_device *proxy_target;
+ struct notifier_block nb;
+};
+
+static char *backlight_proxy_target;
+module_param(backlight_proxy_target, charp, 0);
It seems these module parameters are neither readable nor writable,
is that intentional?
It was intentional that they not be writable, because I didn't want to
have to plumb everything through to handle changing the values after
probe. However, you are right that it could still be useful to set up
the sysfs entries to allow reading the values, as this could be useful
information for someone who wants to check if either of these quirks are
enabled.
+MODULE_PARM_DESC(backlight_proxy_target, "Relay brightness change requests to the named backlight driver, on systems which erroneously report EC backlight control.");
+
+static int max_reprobe_attempts = 128;
Can you elaborate how this number was arrived at?
It's just a medium-small round number. I didn't want probe to return
-EPROBE_DEFER forever if e.g. somebody specified a wrong device name or
if the target device name changes and the entry in the quirks table goes
out of date. On the system I tested this on, the amdgpu_bl1 device was
accessible on the 14th probe attempt. If there's some better value to
plug in here, or if it's actually considered more correct to just never
succeed at probe if the workaround is enabled but the target device can
be found, I'd be happy to change it.
+module_param(max_reprobe_attempts, int, 0);
+MODULE_PARM_DESC(max_reprobe_attempts, "Limit of reprobe attempts when relaying brightness change requests.");
+
+static bool restore_level_on_resume;
+module_param(restore_level_on_resume, bool, 0);
+MODULE_PARM_DESC(restore_level_on_resume, "Restore the backlight level when resuming from suspend, on systems which reset the EC's backlight level on resume.");
+
+static int assign_relay_quirk(const struct dmi_system_id *id)
+{
+ backlight_proxy_target = id->driver_data;
+ return true;
+}
+
+#define PROXY_QUIRK_ENTRY(vendor, product, quirk_data) { \
+ .callback = assign_relay_quirk, \
+ .matches = { \
+ DMI_MATCH(DMI_SYS_VENDOR, vendor), \
+ DMI_MATCH(DMI_PRODUCT_VERSION, product) \
+ }, \
+ .driver_data = quirk_data \
+}
+
+static const struct dmi_system_id proxy_quirk_table[] = {
+ PROXY_QUIRK_ENTRY("LENOVO", "Legion S7 15ACH6", "amdgpu_bl1"),
+ { }
+};
+
+static int assign_restore_quirk(const struct dmi_system_id *id)
+{
+ restore_level_on_resume = true;
+ return true;
+}
+
+#define RESTORE_QUIRK_ENTRY(vendor, product) { \
+ .callback = assign_restore_quirk, \
+ .matches = { \
+ DMI_MATCH(DMI_SYS_VENDOR, vendor), \
+ DMI_MATCH(DMI_PRODUCT_VERSION, product), \
+ } \
+}
+
+static const struct dmi_system_id restore_quirk_table[] = {
+ RESTORE_QUIRK_ENTRY("LENOVO", "Legion S7 15ACH6"),
+ { }
+};
+
/**
* wmi_brightness_notify() - helper function for calling WMI-wrapped ACPI method
* @w: Pointer to the struct wmi_device identified by %WMI_BRIGHTNESS_GUID
@@ -119,9 +185,30 @@ static int wmi_brightness_notify(struct wmi_device *w, enum wmi_brightness_metho
return 0;
}
+static int scale_backlight_level(struct backlight_device *a,
+ struct backlight_device *b)
+{
+ /* because floating point math in the kernel is annoying */
+ const int scaling_factor = 65536;
+ int level = a->props.brightness;
+ int relative_level = level * scaling_factor / a->props.max_brightness;
+
+ return relative_level * b->props.max_brightness / scaling_factor;
+}
Maybe
fixp_linear_interpolate(0, 0, a->props.max_brightness, b->props.max_brightness, a->props.brightness);
? (from `linux/fixp-arith.h`)
Yes, this is exactly what I want; thank you.
+
static int nvidia_wmi_ec_backlight_update_status(struct backlight_device *bd)
{
struct wmi_device *wdev = bl_get_data(bd);
+ struct nvidia_wmi_ec_backlight_priv *priv = dev_get_drvdata(&wdev->dev);
+ struct backlight_device *proxy_target = priv->proxy_target;
+
+ if (proxy_target) {
+ int level = scale_backlight_level(bd, proxy_target);
+
+ if (backlight_device_set_brightness(proxy_target, level))
+ pr_warn("Failed to relay backlight update to \"%s\"",
+ backlight_proxy_target);
+ }
return wmi_brightness_notify(wdev, WMI_BRIGHTNESS_METHOD_LEVEL,
WMI_BRIGHTNESS_MODE_SET,
@@ -147,13 +234,65 @@ static const struct backlight_ops nvidia_wmi_ec_backlight_ops = {
.get_brightness = nvidia_wmi_ec_backlight_get_brightness,
};
+static int nvidia_wmi_ec_backlight_pm_notifier(struct notifier_block *nb, unsigned long event, void *d)
+{
+
+ /*
+ * On some systems, the EC backlight level gets reset to 100% when
+ * resuming from suspend, but the backlight device state still reflects
+ * the pre-suspend value. Refresh the existing state to sync the EC's
+ * state back up with the kernel's.
+ */
+ if (event == PM_POST_SUSPEND) {
+ struct nvidia_wmi_ec_backlight_priv *p;
+
+ p = container_of(nb, struct nvidia_wmi_ec_backlight_priv, nb);
+ return backlight_update_status(p->bl_dev);
`backlight_update_status()` returns a negative errno while the notifier chain
expects something else. It would probably be better to return `NOTIFY_DONE`
in all cases. Currently a suitable error from `backlight_update_status()` will
stop the notifier chain.
Thanks for catching that: I should have paid more attention to the
notifier callback signature.
+ }
+
+ return 0;
+}
+
static int nvidia_wmi_ec_backlight_probe(struct wmi_device *wdev, const void *ctx)
{
+ struct backlight_device *bdev, *target = NULL;
+ struct nvidia_wmi_ec_backlight_priv *priv;
struct backlight_properties props = {};
- struct backlight_device *bdev;
u32 source;
int ret;
+ /*
+ * Check quirks tables to see if this system needs any of the firmware
+ * bug workarounds.
+ */
+
+ /* User-set quirks from the module parameters take precedence */
+ if (!backlight_proxy_target)
+ dmi_check_system(proxy_quirk_table);
+
+ dmi_check_system(restore_quirk_table);
+
+ if (backlight_proxy_target && backlight_proxy_target[0]) {
+ static int num_reprobe_attempts;
+
+ target = backlight_device_get_by_name(backlight_proxy_target);
+
+ if (!target) {
+ /*
+ * The target backlight device might not be ready;
+ * try again and disable backlight proxying if it
+ * fails too many times.
+ */
+ if (num_reprobe_attempts < max_reprobe_attempts) {
+ num_reprobe_attempts++;
+ return -EPROBE_DEFER;
+ }
+
+ pr_warn("Unable to acquire %s after %d attempts. Disabling backlight proxy.",
+ backlight_proxy_target, max_reprobe_attempts);
+ }
+ }
I think `target` is not put in case of error. You probably need to add something like:
if (target) {
ret = devm_add_action_or_reset(&wdev->dev, put_device_wrapper, target);
if (ret < 0)
return ret;
}
+
ret = wmi_brightness_notify(wdev, WMI_BRIGHTNESS_METHOD_SOURCE,
WMI_BRIGHTNESS_MODE_GET, &source);
if (ret)
@@ -188,7 +327,44 @@ static int nvidia_wmi_ec_backlight_probe(struct wmi_device *wdev, const void *ct
&wdev->dev, wdev,
&nvidia_wmi_ec_backlight_ops,
&props);
- return PTR_ERR_OR_ZERO(bdev);
+
+ if (IS_ERR(bdev))
+ return PTR_ERR(bdev);
+
+ priv = kzalloc(sizeof(*priv), GFP_KERNEL);
`devm_kzalloc()` would probably be better and you should check if `!priv`.
+ priv->bl_dev = bdev;
+
+ dev_set_drvdata(&wdev->dev, priv);
+
+ if (target) {
+ int level = scale_backlight_level(target, bdev);
+
+ if (backlight_device_set_brightness(bdev, level))
+ pr_warn("Unable to import initial brightness level from %s.",
+ backlight_proxy_target);
+ priv->proxy_target = target;
+ }
+
+ if (restore_level_on_resume) {
+ priv->nb.notifier_call = nvidia_wmi_ec_backlight_pm_notifier;
+ register_pm_notifier(&priv->nb);
+ }
+
+ return 0;
+}
+
+static void nvidia_wmi_ec_backlight_remove(struct wmi_device *wdev)
+{
+ struct nvidia_wmi_ec_backlight_priv *priv = dev_get_drvdata(&wdev->dev);
+ struct backlight_device *proxy_target = priv->proxy_target;
+
+ if (proxy_target)
+ put_device(&proxy_target->dev);
If you switch to `devm_add_action_or_reset()`, this will not be needed.
+
+ if (priv->nb.notifier_call)
+ unregister_pm_notifier(&priv->nb);
+
+ kfree(priv);
If you switch to `devm_kzalloc()`, this won't be needed.
Thank you, the devm_*() variants are indeed useful.
}
#define WMI_BRIGHTNESS_GUID "603E9613-EF25-4338-A3D0-C46177516DB7"
@@ -204,6 +380,7 @@ static struct wmi_driver nvidia_wmi_ec_backlight_driver = {
.name = "nvidia-wmi-ec-backlight",
},
.probe = nvidia_wmi_ec_backlight_probe,
+ .remove = nvidia_wmi_ec_backlight_remove,
.id_table = nvidia_wmi_ec_backlight_id_table,
};
module_wmi_driver(nvidia_wmi_ec_backlight_driver);
--
2.27.0
Lastly, is it expected that these bugs will be properly fixed?
Possibly, but I wouldn't hold out hope for it for an issue at this scale
on an already shipping system.
Regards,
Barnabás Pőcze
