[PATCH 3/7] rtc: pm8xxx: add support for uefi offset

Johan Hovold
2025-01-20T14:42:48Z

On many Qualcomm platforms the PMIC RTC control and time registers are
read-only so that the RTC time can not be updated. Instead an offset
needs be stored in some machine-specific non-volatile memory, which the
driver can take into account.

Add support for storing a 32-bit offset from the GPS time epoch in a
UEFI variable so that the RTC time can be set on such platforms.

The UEFI variable is

882f8c2b-9646-435f-8de5-f208ff80c1bd-RTCInfo

and holds a 12-byte structure where the first four bytes is a GPS time
offset in little-endian byte order.

Note that this format is not arbitrary as the variable is shared with
the UEFI firmware (and Windows).

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
drivers/rtc/rtc-pm8xxx.c | 125 +++++++++++++++++++++++++++++++++++++--
include/linux/rtc.h | 1 +
2 files changed, 121 insertions(+), 5 deletions(-)

diff --git a/drivers/rtc/rtc-pm8xxx.c b/drivers/rtc/rtc-pm8xxx.c
index 2f32187ecc8d..be1983bf35cd 100644
--- a/drivers/rtc/rtc-pm8xxx.c
+++ b/drivers/rtc/rtc-pm8xxx.c
@@ -5,6 +5,7 @@
* Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
* Copyright (c) 2023, Linaro Limited
*/
+#include <linux/efi.h>
#include <linux/of.h>
#include <linux/module.h>
#include <linux/nvmem-consumer.h>
@@ -16,9 +17,10 @@
#include <linux/regmap.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
-
#include <linux/unaligned.h>

+#include <asm/byteorder.h>
+
/* RTC_CTRL register bit fields */
#define PM8xxx_RTC_ENABLE BIT(7)
#define PM8xxx_RTC_ALARM_CLEAR BIT(0)
@@ -46,14 +48,21 @@ struct pm8xxx_rtc_regs {
unsigned int alarm_en;
};

+struct qcom_uefi_rtc_info {
+ __le32 offset_gps;
+ u8 reserved[8];
+} __packed;
+
/**
* struct pm8xxx_rtc - RTC driver internal structure
* @rtc: RTC device
* @regmap: regmap used to access registers
* @allow_set_time: whether the time can be set
+ * @use_uefi: use UEFI variable as fallback for offset
* @alarm_irq: alarm irq number
* @regs: register description
* @dev: device structure
+ * @rtc_info: qcom uefi rtc-info structure
* @nvmem_cell: nvmem cell for offset
* @offset: offset from epoch in seconds
*/
@@ -61,13 +70,101 @@ struct pm8xxx_rtc {
struct rtc_device *rtc;
struct regmap *regmap;
bool allow_set_time;
+ bool use_uefi;
int alarm_irq;
const struct pm8xxx_rtc_regs *regs;
struct device *dev;
+ struct qcom_uefi_rtc_info rtc_info;
struct nvmem_cell *nvmem_cell;
u32 offset;
};

+#ifdef CONFIG_EFI
+
+MODULE_IMPORT_NS("EFIVAR");
+
+#define QCOM_UEFI_NAME L"RTCInfo"
+#define QCOM_UEFI_GUID EFI_GUID(0x882f8c2b, 0x9646, 0x435f, \
+ 0x8d, 0xe5, 0xf2, 0x08, 0xff, 0x80, 0xc1, 0xbd)
+#define QCOM_UEFI_ATTRS (EFI_VARIABLE_NON_VOLATILE | \
+ EFI_VARIABLE_BOOTSERVICE_ACCESS | \
+ EFI_VARIABLE_RUNTIME_ACCESS)
+
+static int pm8xxx_rtc_read_uefi_offset(struct pm8xxx_rtc *rtc_dd)
+{
+ struct qcom_uefi_rtc_info *rtc_info = &rtc_dd->rtc_info;
+ unsigned long size = sizeof(*rtc_info);
+ struct device *dev = rtc_dd->dev;
+ efi_status_t status;
+ u32 offset_gps;
+ int rc;
+
+ rc = efivar_lock();
+ if (rc)
+ return rc;
+
+ status = efivar_get_variable(QCOM_UEFI_NAME, &QCOM_UEFI_GUID, NULL,
+ &size, rtc_info);
+ efivar_unlock();
+
+ if (status != EFI_SUCCESS) {
+ dev_dbg(dev, "failed to read UEFI offset: %lu\n", status);
+ return efi_status_to_err(status);
+ }
+
+ if (size != sizeof(*rtc_info)) {
+ dev_dbg(dev, "unexpected UEFI structure size %lu\n", size);
+ return -EINVAL;
+ }
+
+ dev_dbg(dev, "uefi_rtc_info = %*ph\n", (int)size, rtc_info);
+
+ /* Convert from GPS to Unix time offset */
+ offset_gps = le32_to_cpu(rtc_info->offset_gps);
+ rtc_dd->offset = offset_gps + (u32)RTC_TIMESTAMP_EPOCH_GPS;
+
+ return 0;
+}
+
+static int pm8xxx_rtc_write_uefi_offset(struct pm8xxx_rtc *rtc_dd, u32 offset)
+{
+ struct qcom_uefi_rtc_info *rtc_info = &rtc_dd->rtc_info;
+ unsigned long size = sizeof(*rtc_info);
+ struct device *dev = rtc_dd->dev;
+ efi_status_t status;
+ u32 offset_gps;
+
+ /* Convert from Unix to GPS time offset */
+ offset_gps = offset - (u32)RTC_TIMESTAMP_EPOCH_GPS;
+
+ rtc_info->offset_gps = cpu_to_le32(offset_gps);
+
+ dev_dbg(dev, "efi_rtc_info = %*ph\n", (int)size, rtc_info);
+
+ status = efivar_set_variable(QCOM_UEFI_NAME, &QCOM_UEFI_GUID,
+ QCOM_UEFI_ATTRS, size, rtc_info);
+ if (status != EFI_SUCCESS) {
+ dev_dbg(dev, "failed to write UEFI offset: %lx\n", status);
+ return efi_status_to_err(status);
+ }
+
+ return 0;
+}
+
+#else /* CONFIG_EFI */
+
+static int pm8xxx_rtc_read_uefi_offset(struct pm8xxx_rtc *rtc_dd)
+{
+ return -ENODEV;
+}
+
+static int pm8xxx_rtc_write_uefi_offset(struct pm8xxx_rtc *rtc_dd, u32 offset)
+{
+ return -ENODEV;
+}
+
+#endif /* CONFIG_EFI */
+
static int pm8xxx_rtc_read_nvmem_offset(struct pm8xxx_rtc *rtc_dd)
{
size_t len;
@@ -112,10 +209,13 @@ static int pm8xxx_rtc_write_nvmem_offset(struct pm8xxx_rtc *rtc_dd, u32 offset)

static int pm8xxx_rtc_read_offset(struct pm8xxx_rtc *rtc_dd)
{
- if (!rtc_dd->nvmem_cell)
+ if (!rtc_dd->nvmem_cell && !rtc_dd->use_uefi)
return 0;

- return pm8xxx_rtc_read_nvmem_offset(rtc_dd);
+ if (rtc_dd->nvmem_cell)
+ return pm8xxx_rtc_read_nvmem_offset(rtc_dd);
+ else
+ return pm8xxx_rtc_read_uefi_offset(rtc_dd);
}

static int pm8xxx_rtc_read_raw(struct pm8xxx_rtc *rtc_dd, u32 *secs)
@@ -155,7 +255,7 @@ static int pm8xxx_rtc_update_offset(struct pm8xxx_rtc *rtc_dd, u32 secs)
u32 offset;
int rc;

- if (!rtc_dd->nvmem_cell)
+ if (!rtc_dd->nvmem_cell && !rtc_dd->use_uefi)
return -ENODEV;

rc = pm8xxx_rtc_read_raw(rtc_dd, &raw_secs);
@@ -167,7 +267,11 @@ static int pm8xxx_rtc_update_offset(struct pm8xxx_rtc *rtc_dd, u32 secs)
if (offset == rtc_dd->offset)
return 0;

- rc = pm8xxx_rtc_write_nvmem_offset(rtc_dd, offset);
+ if (rtc_dd->nvmem_cell)
+ rc = pm8xxx_rtc_write_nvmem_offset(rtc_dd, offset);
+ else
+ rc = pm8xxx_rtc_write_uefi_offset(rtc_dd, offset);
+
if (rc)
return rc;

@@ -486,6 +590,17 @@ static int pm8xxx_rtc_probe(struct platform_device *pdev)
if (rc != -ENOENT)
return rc;
rtc_dd->nvmem_cell = NULL;
+
+ /* Use UEFI storage as fallback if available */
+ rtc_dd->use_uefi = of_property_read_bool(pdev->dev.of_node,
+ "qcom,uefi-rtc-info");
+ }
+
+ if (rtc_dd->use_uefi && !efivar_is_available()) {
+ if (IS_ENABLED(CONFIG_EFI))
+ return -EPROBE_DEFER;
+ dev_warn(&pdev->dev, "efivars not available\n");
+ rtc_dd->use_uefi = false;
}

rtc_dd->regs = match->data;
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 3f4d315aaec9..95da051fb155 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -170,6 +170,7 @@ struct rtc_device {
/* useful timestamps */
#define RTC_TIMESTAMP_BEGIN_0000 -62167219200ULL /* 0000-01-01 00:00:00 */
#define RTC_TIMESTAMP_BEGIN_1900 -2208988800LL /* 1900-01-01 00:00:00 */
+#define RTC_TIMESTAMP_EPOCH_GPS 315964800LL /* 1980-01-06 00:00:00 */
#define RTC_TIMESTAMP_BEGIN_2000 946684800LL /* 2000-01-01 00:00:00 */
#define RTC_TIMESTAMP_END_2063 2966371199LL /* 2063-12-31 23:59:59 */
#define RTC_TIMESTAMP_END_2079 3471292799LL /* 2079-12-31 23:59:59 */
--
2.45.2