pstore: persistent storage for Linux

Integrate into Linux pstore system to store kernel
crash logs in EMC memory.

README.md

@@ -24,6 +24,7 @@ The following features are implemented:
   - battery charger (BQ25713)
   - external power supply with USB PD (STUSB4500) and USB charger detector (MAX14636)
   - charging mode with system power off
+  - Linux pstore (persistent storage) integration for kernel panic logs
   - configuration storage in flash memory
   - full devicetree integration
 

openemc-bootloader/emc-bootloader.x

@@ -50,5 +50,12 @@ SECTIONS
     KEEP(*(.defmt_log .defmt_log.*));
     . = ALIGN(8);
   } > RAM
+
+  /* Pstore buffer. */
+  .pstore (NOLOAD) : ALIGN(8)
+  {
+    KEEP(*(.pstore .pstore.*));
+    . = ALIGN(8);
+  } > RAM
 }
 INSERT BEFORE .data;

openemc-bootloader/src/main.rs

@@ -102,6 +102,12 @@ pub static mut BOOTLOADER_LOG: core::mem::MaybeUninit<
 pub static mut LOG: core::mem::MaybeUninit<defmt_ringbuf::RingBuffer<{ openemc_shared::LOG_SIZE }>> =
     core::mem::MaybeUninit::uninit();
 
+/// Platform store.
+#[used]
+#[no_mangle]
+#[link_section = ".pstore"]
+pub static mut PSTORE: [u8; openemc_shared::PSTORE_SIZE] = [0; openemc_shared::PSTORE_SIZE];
+
 /// Signature value for backup register.
 pub const BACKUP_REG_SIGNATURE_VALUE: u16 = 0xb001;
 

openemc-driver/Makefile

@@ -1,6 +1,6 @@
 obj-m += openemc.o openemc_adc.o openemc_battery.o openemc_gpio.o \
 	openemc_pinctrl.o openemc_power.o openemc_pwm.o openemc_rtc.o \
-	openemc_supply.o openemc_wdt.o
+	openemc_supply.o openemc_wdt.o openemc_pstore.o
 
 all:
 	make -C ${LINUX_DIR} M=$(PWD) modules

openemc-driver/openemc.h

@@ -116,6 +116,12 @@
 #define OPENEMC_SUPPLY_CURRENT 0x95
 #define OPENEMC_SUPPLY_CONNECT_DATA 0x96
 
+/* Platform store register definitions */
+#define OPENEMC_PSTORE_SIZE 0xa0
+#define OPENEMC_PSTORE_IO_ADDRESS 0xa1
+#define OPENEMC_PSTORE_IO_SIZE 0xa2
+#define OPENEMC_PSTORE_IO 0xa3
+
 /* Board IO register definitions */
 #define OPENEMC_BOARD_IO 0xe0
 #define OPENEMC_BOARD_IO_STATUS 0xe1

openemc-driver/openemc_pstore.c

@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Platform store driver for OpenEMC
+ *
+ * Copyright (C) 2022-2024 Sebastian Urban <surban@surban.net>
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/of_device.h>
+#include <linux/pstore_blk.h>
+#include <linux/delay.h>
+
+#include "openemc.h"
+
+static const struct of_device_id openemc_pstore_of_match[] = {
+	{ .compatible = "openemc,openemc_pstore" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, openemc_pstore_of_match);
+
+static struct openemc_pstore_context {
+	struct openemc *emc;
+	struct pstore_blk_config info;
+	struct pstore_device_info dev;
+} oops_cxt;
+
+static ssize_t openemc_pstore_read(char *buf, size_t size, loff_t off)
+{
+	struct openemc *emc = oops_cxt.emc;
+	u16 io_size = 0;
+	size_t pos = 0;
+	int ret;
+
+	ret = openemc_write_u16(emc, OPENEMC_PSTORE_IO_ADDRESS, off);
+	if (ret < 0)
+		return ret;
+
+	while (pos < size) {
+		u16 new_io_size =
+			min_t(size_t, OPENEMC_MAX_DATA_SIZE, size - pos);
+		if (io_size != new_io_size) {
+			ret = openemc_write_u16(emc, OPENEMC_PSTORE_IO_SIZE,
+						new_io_size);
+			if (ret < 0)
+				return ret;
+
+			io_size = new_io_size;
+		}
+
+		ret = openemc_read_data(emc, OPENEMC_PSTORE_IO, io_size,
+					buf + pos);
+		if (ret < 0)
+			return ret;
+
+		pos += io_size;
+	}
+
+	return size;
+}
+
+static ssize_t openemc_pstore_write(const char *buf, size_t size, loff_t off)
+{
+	struct openemc *emc = oops_cxt.emc;
+	u16 io_size = 0;
+	size_t pos = 0;
+	int ret;
+
+	ret = openemc_write_u16(emc, OPENEMC_PSTORE_IO_ADDRESS, off);
+	if (ret < 0)
+		return ret;
+
+	while (pos < size) {
+		u16 new_io_size =
+			min_t(size_t, OPENEMC_MAX_DATA_SIZE, size - pos);
+		if (io_size != new_io_size) {
+			ret = openemc_write_u16(emc, OPENEMC_PSTORE_IO_SIZE,
+						new_io_size);
+			if (ret < 0)
+				return ret;
+
+			io_size = new_io_size;
+		}
+
+		ret = openemc_write_data(emc, OPENEMC_PSTORE_IO, io_size,
+					 buf + pos);
+		if (ret < 0)
+			return ret;
+
+		pos += io_size;
+	}
+
+	return size;
+}
+
+static ssize_t openemc_pstore_panic_write(const char *buf, size_t size,
+					  loff_t off)
+{
+	struct openemc *emc = oops_cxt.emc;
+
+	if (mutex_is_locked(&emc->req_lock)) {
+		pr_emerg("Breaking OpenEMC lock for panic write\n");
+		mutex_unlock(&emc->req_lock);
+	}
+
+	return openemc_pstore_write(buf, size, off);
+}
+
+static int openemc_pstore_probe(struct platform_device *pdev)
+{
+	const struct of_device_id *match;
+	struct openemc_pstore_context *cxt = &oops_cxt;
+	u16 total_size;
+	int ret;
+
+	match = of_match_node(openemc_pstore_of_match, pdev->dev.of_node);
+	if (!match)
+		return -ENXIO;
+
+	cxt->emc = dev_get_drvdata(pdev->dev.parent);
+
+	ret = pstore_blk_get_config(&cxt->info);
+	if (ret)
+		return ret;
+
+	if (!cxt->info.kmsg_size) {
+		pr_err("no backend enabled (kmsg_size is 0)\n");
+		return -EINVAL;
+	}
+
+	ret = openemc_read_u16(cxt->emc, OPENEMC_PSTORE_SIZE, &total_size);
+	if (ret < 0)
+		return ret;
+
+	if (total_size < 4096) {
+		dev_err(&pdev->dev, "OpenEMC pstore buffer is too small");
+		return -EINVAL;
+	}
+
+	cxt->dev.flags = PSTORE_FLAGS_DMESG;
+	cxt->dev.zone.read = openemc_pstore_read;
+	cxt->dev.zone.write = openemc_pstore_write;
+	cxt->dev.zone.erase = NULL;
+	cxt->dev.zone.panic_write = openemc_pstore_panic_write;
+	cxt->dev.zone.total_size = total_size;
+
+	ret = register_pstore_device(&cxt->dev);
+	if (ret) {
+		dev_err(&pdev->dev, "cannot register pstore device: %d\n", ret);
+		return ret;
+	}
+
+	dev_info(&pdev->dev, "OpenEMC pstore registered with %d bytes\n",
+		 total_size);
+
+	return 0;
+}
+
+static int openemc_pstore_remove(struct platform_device *pdev)
+{
+	struct openemc_pstore_context *cxt = &oops_cxt;
+
+	unregister_pstore_device(&cxt->dev);
+	cxt->emc = NULL;
+
+	return 0;
+}
+
+static struct platform_driver openemc_pstore_driver = {
+	.driver = {
+		.name = "openemc_pstore",
+		.of_match_table = of_match_ptr(openemc_pstore_of_match),
+	},
+	.probe = openemc_pstore_probe,
+	.remove = openemc_pstore_remove,
+};
+module_platform_driver(openemc_pstore_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sebastian Urban <surban@surban.net>");
+MODULE_DESCRIPTION("OpenEMC Platform Store");
+MODULE_VERSION("0.1");

openemc-firmware/memory.x

@@ -27,6 +27,13 @@ SECTIONS
     KEEP(*(.defmt_log .defmt_log.*));
     . = ALIGN(8);
   } > RAM
+
+  /* Pstore buffer. */
+  .pstore (NOLOAD) : ALIGN(8)
+  {
+    KEEP(*(.pstore .pstore.*));
+    . = ALIGN(8);
+  } > RAM
 }
 INSERT BEFORE .data;
 

openemc-firmware/src/i2c_reg_slave.rs

@@ -271,6 +271,11 @@ impl<const BUFFER: usize> Deref for Response<BUFFER> {
 }
 
 impl<const BUFFER: usize> Response<BUFFER> {
+    /// Buffer size.
+    pub const fn buffer() -> usize {
+        BUFFER
+    }
+
     /// Provides the register value.
     ///
     /// The length of the value must not exceed `BUFFER`.

openemc-firmware/src/main.rs

@@ -50,6 +50,7 @@ mod i2c_reg_slave;
 mod i2c_slave;
 mod irq;
 mod pio;
+mod pstore;
 mod pwm;
 mod reg;
 mod rtc;
@@ -123,7 +124,7 @@ static MFD_CELL_PREFIX: &[u8] = b"openemc,openemc_";
 
 /// MFD cells.
 static MFD_CELLS: &[&[u8]] =
-    &[b"adc", b"battery", b"gpio", b"pinctrl", b"power", b"pwm", b"rtc", b"supply", b"wdt"];
+    &[b"adc", b"battery", b"gpio", b"pinctrl", b"power", b"pwm", b"rtc", b"supply", b"wdt", b"pstore"];
 
 /// Supported EMC models.
 static EMC_MODELS: &[u8] = &[0x01, 0xd1];
@@ -160,6 +161,12 @@ static mut BOOTLOADER_LOG_REF: Option<
     &'static mut defmt_ringbuf::RingBuffer<{ openemc_shared::BOOTLOADER_LOG_SIZE }>,
 > = None;
 
+/// Platform store.
+#[used]
+#[no_mangle]
+#[link_section = ".pstore"]
+pub static mut PSTORE: [u8; openemc_shared::PSTORE_SIZE] = [0; openemc_shared::PSTORE_SIZE];
+
 extern "C" {
     /// Space reserved for bootloader (from linker).
     pub static __bootloader_max_size: c_void;
@@ -327,6 +334,8 @@ mod app {
         bootloader_crc32: u32,
         /// Power on due to charger attachment.
         charger_attachment_power_on: bool,
+        /// Persistent platform store.
+        pstore: pstore::Pstore<'static>,
     }
 
     /// Exclusive resources.
@@ -682,6 +691,14 @@ mod app {
             ThisBoard::PWM_TIMERS[3].then(|| PwmTimer::new(pwm::Timer::Timer4, &clocks)),
         ];
 
+        // Initialize platform store.
+        let pstore = unsafe {
+            use core::ptr::addr_of_mut;
+            // SAFETY: PSTORE is only accessed here and nowhere else.
+            pstore::Pstore::new(&mut *addr_of_mut!(PSTORE))
+        };
+        defmt::info!("Platform store of size {} bytes", pstore.data.len());
+
         // Configure IRQ pin.
         let mut usable_exti = 0b0000_0000_0000_1111_1111_1111_1111_1111;
         board.limit_usable_exti(&mut usable_exti);
@@ -755,6 +772,7 @@ mod app {
                 undervoltage_power_off: false,
                 bootloader_crc32,
                 charger_attachment_power_on,
+                pstore,
             },
             Local { i2c_reg_slave, adc, adc_inp, ugpio, pwm_timers },
             init::Monotonics(mono),
@@ -1495,6 +1513,7 @@ mod app {
             cfg,
             &bootloader_crc32,
             &charger_attachment_power_on,
+            pstore,
         ],
         priority = 2,
     )]
@@ -1906,6 +1925,33 @@ mod app {
             Event::Write { reg: reg::SUPPLY_CONNECT_DATA, value } => {
                 cx.shared.power_supply_connect_data.lock(|connect| *connect = value.as_u8() != 0);
             }
+            Event::Read { reg: reg::PSTORE_SIZE } => {
+                cx.shared.pstore.lock(|pstore| respond_u16(pstore.data.len() as _));
+            }
+            Event::Read { reg: reg::PSTORE_IO_ADDRESS } => {
+                cx.shared.pstore.lock(|pstore| respond_u16(pstore.io_address as _));
+            }
+            Event::Write { reg: reg::PSTORE_IO_ADDRESS, value } => {
+                cx.shared.pstore.lock(|pstore| pstore.io_address = value.as_u16() as _);
+            }
+            Event::Read { reg: reg::PSTORE_IO_SIZE } => {
+                cx.shared.pstore.lock(|pstore| respond_u16(pstore.io_size as _));
+            }
+            Event::Write { reg: reg::PSTORE_IO_SIZE, value } => {
+                cx.shared.pstore.lock(|pstore| pstore.io_size = value.as_u16() as _);
+            }
+            Event::Read { reg: reg::PSTORE_IO } => {
+                cx.shared.pstore.lock(|pstore| {
+                    let mut buf = [0; I2C_BUFFER_SIZE];
+                    pstore.read(&mut buf);
+                    respond_slice(&buf);
+                });
+            }
+            Event::Write { reg: reg::PSTORE_IO, value } => {
+                cx.shared.pstore.lock(|pstore| {
+                    pstore.write(&value);
+                });
+            }
             Event::Read { reg: reg::BOARD_IO } => {
                 cx.shared.board.lock(|board| {
                     let data = board.io_read();