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SubjectRe: [PATCH v2 1/2] platform/chrome: Add driver for ChromeOS privacy-screen
Hi Rajat,

On Fri, Dec 17, 2021 at 12:28:49PM -0800, Rajat Jain wrote:
> This adds the ACPI driver for the ChromeOS privacy screen that is
> present on some chromeos devices.
>
> Note that ideally, we'd want this privacy screen driver to be probed
> BEFORE the drm probe in order to avoid a drm probe deferral:
> https://hansdegoede.livejournal.com/25948.html
>
> In practise, I found that ACPI drivers are bound to their devices AFTER
> the drm probe on chromebooks. So on chromebooks with privacy-screen,
> this patch along with the next one in this series results in a probe
> deferral of about 250ms for i915 driver. However, it did not result in
> any user noticeable delay of splash screen in my personal experience.
>
> In future if this probe deferral turns out to be an issue, we can
> consider turning this ACPI driver into something that is probed
> earlier than the drm drivers.
>
> Signed-off-by: Rajat Jain <rajatja@google.com>
> ---
> v2: * Reword the commit log
> * Make the Kconfig into a tristate
> * Reorder the patches in the series.
>
> drivers/platform/chrome/Kconfig | 9 ++
> drivers/platform/chrome/Makefile | 1 +
> drivers/platform/chrome/chromeos_priv_scrn.c | 132 +++++++++++++++++++
> 3 files changed, 142 insertions(+)
> create mode 100644 drivers/platform/chrome/chromeos_priv_scrn.c
>
> diff --git a/drivers/platform/chrome/Kconfig b/drivers/platform/chrome/Kconfig
> index ccc23d8686e8..d1c209a45a62 100644
> --- a/drivers/platform/chrome/Kconfig
> +++ b/drivers/platform/chrome/Kconfig
> @@ -243,6 +243,15 @@ config CROS_USBPD_NOTIFY
> To compile this driver as a module, choose M here: the
> module will be called cros_usbpd_notify.
>
> +config CHROMEOS_PRIVACY_SCREEN
> + tristate "ChromeOS Privacy Screen support"
> + depends on ACPI
> + depends on DRM
> + select DRM_PRIVACY_SCREEN
> + help
> + This driver provides the support needed for the in-built electronic
> + privacy screen that is present on some ChromeOS devices.
> +
> source "drivers/platform/chrome/wilco_ec/Kconfig"
>
> endif # CHROMEOS_PLATFORMS
> diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
> index f901d2e43166..cfa0bb4e9e34 100644
> --- a/drivers/platform/chrome/Makefile
> +++ b/drivers/platform/chrome/Makefile
> @@ -4,6 +4,7 @@
> CFLAGS_cros_ec_trace.o:= -I$(src)
>
> obj-$(CONFIG_CHROMEOS_LAPTOP) += chromeos_laptop.o
> +obj-$(CONFIG_CHROMEOS_PRIVACY_SCREEN) += chromeos_priv_scrn.o
> obj-$(CONFIG_CHROMEOS_PSTORE) += chromeos_pstore.o
> obj-$(CONFIG_CHROMEOS_TBMC) += chromeos_tbmc.o
> obj-$(CONFIG_CROS_EC) += cros_ec.o
> diff --git a/drivers/platform/chrome/chromeos_priv_scrn.c b/drivers/platform/chrome/chromeos_priv_scrn.c
> new file mode 100644
> index 000000000000..a4cbf5c79c2a
> --- /dev/null
> +++ b/drivers/platform/chrome/chromeos_priv_scrn.c

I think we can spare a few more characters :) chromeos_privacy_screen.c
maybe?

And also see if maybe variables in the code are not that unseemly long
even if not abbreviated?

> @@ -0,0 +1,132 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * chromeos_priv_scrn.c - ChromeOS Privacy Screen support

I'd avoid mentioning file name as those tend to change.

> + *
> + * Copyright (C) 2022 The Chromium OS Authors

This is not correct copyright for kernel contributions. It should be
attributed to "Google LLC". Note that it is different from CrOS
userspace.

> + *
> + */
> +
> +#include <linux/acpi.h>
> +#include <drm/drm_privacy_screen_driver.h>
> +
> +/*
> + * The DSM (Define Specific Method) constants below are the agreed API with
> + * the firmware team, on how to control privacy screen using ACPI methods.
> + */
> +#define PRIV_SCRN_DSM_REVID 1 /* DSM version */
> +#define PRIV_SCRN_DSM_FN_GET_STATUS 1 /* Get privacy screen status */
> +#define PRIV_SCRN_DSM_FN_ENABLE 2 /* Enable privacy screen */
> +#define PRIV_SCRN_DSM_FN_DISABLE 3 /* Disable privacy screen */
> +
> +static const guid_t chromeos_priv_scrn_dsm_guid =
> + GUID_INIT(0xc7033113, 0x8720, 0x4ceb,
> + 0x90, 0x90, 0x9d, 0x52, 0xb3, 0xe5, 0x2d, 0x73);
> +
> +static void
> +chromeos_priv_scrn_get_hw_state(struct drm_privacy_screen *drm_priv_scrn)
> +{
> + union acpi_object *obj;
> + acpi_handle handle;
> + struct device *priv_scrn = drm_priv_scrn->dev.parent;

This is really bad that we need to poke into internals of
drm_privacy_screen to get to "our" device. I think there is only one
consume of the privacy screen API at the moment, the thinkpad driver, so
maybe it is not too late to change drm_privacy_screen_register() to
either accept instance of struct drm_privacy_screen (which then could be
embedded into something) or accept a void pointer to attach arbitrary
data to it, and then add drm_privacy_screen_get_drvdata() to get to that
pointer.

> +
> + if (!priv_scrn)
> + return;

This should not happen regardless.

> +
> + handle = acpi_device_handle(to_acpi_device(priv_scrn));
> + obj = acpi_evaluate_dsm(handle, &chromeos_priv_scrn_dsm_guid,
> + PRIV_SCRN_DSM_REVID,
> + PRIV_SCRN_DSM_FN_GET_STATUS, NULL);
> + if (!obj) {
> + dev_err(priv_scrn, "_DSM failed to get privacy-screen state\n");

Can we do something about it? A dedicated status? Also, can we print
ACPI-specific error?

> + return;
> + }
> +
> + if (obj->type != ACPI_TYPE_INTEGER)
> + dev_err(priv_scrn, "Bad _DSM to get privacy-screen state\n");

Same here.

> + else if (obj->integer.value == 1)
> + drm_priv_scrn->hw_state = drm_priv_scrn->sw_state =
> + PRIVACY_SCREEN_ENABLED;
> + else
> + drm_priv_scrn->hw_state = drm_priv_scrn->sw_state =
> + PRIVACY_SCREEN_DISABLED;
> +
> + ACPI_FREE(obj);
> +}
> +
> +static int
> +chromeos_priv_scrn_set_sw_state(struct drm_privacy_screen *drm_priv_scrn,
> + enum drm_privacy_screen_status state)
> +{
> + union acpi_object *obj = NULL;
> + acpi_handle handle;
> + struct device *priv_scrn = drm_priv_scrn->dev.parent;
> +
> + if (!priv_scrn)
> + return -ENODEV;

This should not happen regardless.

> +
> + handle = acpi_device_handle(to_acpi_device(priv_scrn));
> +
> + if (state == PRIVACY_SCREEN_DISABLED) {
> + obj = acpi_evaluate_dsm(handle, &chromeos_priv_scrn_dsm_guid,
> + PRIV_SCRN_DSM_REVID,
> + PRIV_SCRN_DSM_FN_DISABLE, NULL);
> + } else if (state == PRIVACY_SCREEN_ENABLED) {
> + obj = acpi_evaluate_dsm(handle, &chromeos_priv_scrn_dsm_guid,
> + PRIV_SCRN_DSM_REVID,
> + PRIV_SCRN_DSM_FN_ENABLE, NULL);
> + } else {
> + dev_err(priv_scrn, "Bad attempt to set privacy-screen status\n");
> + return -EINVAL;

Print state to aid in tracking bugs?

> + }
> +
> + if (!obj) {
> + dev_err(priv_scrn, "_DSM failed to set privacy-screen state\n");

Can we print ACPI-specific error?

> + return -EIO;
> + }
> +
> + drm_priv_scrn->hw_state = drm_priv_scrn->sw_state = state;
> + ACPI_FREE(obj);
> + return 0;
> +}
> +
> +static const struct drm_privacy_screen_ops chromeos_priv_scrn_ops = {
> + .get_hw_state = chromeos_priv_scrn_get_hw_state,
> + .set_sw_state = chromeos_priv_scrn_set_sw_state,
> +};
> +
> +static int chromeos_priv_scrn_add(struct acpi_device *adev)
> +{
> + struct drm_privacy_screen *drm_priv_scrn =
> + drm_privacy_screen_register(&adev->dev, &chromeos_priv_scrn_ops);
> +
> + if (IS_ERR(drm_priv_scrn)) {
> + dev_err(&adev->dev, "Error registering privacy-screen\n");
> + return PTR_ERR(drm_priv_scrn);
> + }
> +
> + dev_info(&adev->dev, "registered privacy-screen '%s'\n",
> + dev_name(&drm_priv_scrn->dev));

I don't think we need be this noisy.

> +
> + return 0;
> +}
> +
> +static const struct acpi_device_id chromeos_priv_scrn_device_ids[] = {
> + {"GOOG0010", 0}, /* Google's electronic privacy screen for eDP-1 */
> + {}
> +};
> +MODULE_DEVICE_TABLE(acpi, chromeos_priv_scrn_device_ids);
> +
> +static struct acpi_driver chromeos_priv_scrn_driver = {
> + .name = "chromeos_priv_scrn_drvr",
> + .class = "ChromeOS",
> + .ids = chromeos_priv_scrn_device_ids,
> + .ops = {
> + .add = chromeos_priv_scrn_add,

We don't need any cleanup?

> + },
> +};
> +
> +module_acpi_driver(chromeos_priv_scrn_driver);
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("ChromeOS ACPI Privacy Screen driver");
> +MODULE_AUTHOR("Rajat Jain <rajatja@google.com>");
> --
> 2.34.1.307.g9b7440fafd-goog
>

Thanks.

--
Dmitry

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