This patch allows loading user defined SSDTs from the first,
uncompressed, initrd. The SSDT aml code must be stored in files under
the /kernel/firmware/acpi/overlay path.
Signed-off-by: Octavian Purdila <octavian.purdila@xxxxxxxxx>
---
Documentation/acpi/ssdt-overlays.txt | 94 ++++++++++++++++++++++++++++++++++++
drivers/acpi/bus.c | 63 ++++++++++++++++++++++++
2 files changed, 157 insertions(+)
create mode 100644 Documentation/acpi/ssdt-overlays.txt
diff --git a/Documentation/acpi/ssdt-overlays.txt b/Documentation/acpi/ssdt-overlays.txt
new file mode 100644
index 0000000..a94c3f9
--- /dev/null
+++ b/Documentation/acpi/ssdt-overlays.txt
@@ -0,0 +1,94 @@
+
+In order to support ACPI open-ended hardware configurations (e.g. development
+boards) we need a way to augment the ACPI configuration provided by the firmware
+image. A common example is connecting sensors on I2C / SPI buses on development
+boards.
+
+Although this can be accomplished by creating a kernel platform driver or
+recompiling the firmware image with updated ACPI tables, neither is practical:
+the former proliferates board specific kernel code while the latter requires
+access to firmware tools which are often not publicly available.
+
+Because ACPI supports external references in AML code a more practical
+way to augment firmware ACPI configuration is by dynamically loading
+user defined SSDT tables that contain the board specific information.
+
+For example, to enumerate a Bosch BMA222E accelerometer on the I2C bus of the
+Minnowboard MAX development board exposed via the LSE connector [1], the
+following ASL code can be used:
+
+DefinitionBlock ("minnowmax.aml", "SSDT", 1, "Vendor", "Accel", 0x00000003)
+{
+ External (\_SB.I2C6, DeviceObj)
+
+ Scope (\_SB.I2C6)
+ {
+ Device (STAC)
+ {
+ Name (_ADR, Zero)
+ Name (_HID, "BMA222E")
+
+ Method (_CRS, 0, Serialized)
+ {
+ Name (RBUF, ResourceTemplate ()
+ {
+ I2cSerialBus (0x0018, ControllerInitiated, 0x00061A80,
+ AddressingMode7Bit, "\\_SB.I2C6", 0x00,
+ ResourceConsumer, ,)
+ GpioInt (Edge, ActiveHigh, Exclusive, PullDown, 0x0000,
+ "\\_SB.GPO2", 0x00, ResourceConsumer, , )
+ { // Pin list
+ 0
+ }
+ })
+ Return (RBUF)
+ }
+ }
+ }
+}
+
+which can then be compiled to AML binary format:
+
+$ iasl minnowmax.asl
+
+Intel ACPI Component Architecture
+ASL Optimizing Compiler version 20140214-64 [Mar 29 2014]
+Copyright (c) 2000 - 2014 Intel Corporation
+
+ASL Input: minnomax.asl - 30 lines, 614 bytes, 7 keywords
+AML Output: minnowmax.aml - 165 bytes, 6 named objects, 1 executable opcodes
+
+[1] http://wiki.minnowboard.org/MinnowBoard_MAX#Low_Speed_Expansion_Connector_.28Top.29
+
+The resulting AML code can then be loaded by the kernel using one of the methods
+below.
+
+== Loading ACPI SSDTs from initrd ==
+
+This option allows loading of user defined SSDTs from initrd and it is useful
+when the system does not support EFI or when there is not enough EFI storage.
+
+It works in a similar way with initrd based ACPI tables overrides: SSDT aml code
+must be placed in the first, uncompressed, initrd under the
+"kernel/firmware/acpi/overlay" path. We use a different path than the initrd
+tables override to avoid conflicts with the override feature.
+
+Multiple files can be used and this will translate in loading multiple
+tables. Only tables with the SSDT signature will be loaded.
+
+Here is an example:
+
+# Add the raw ACPI tables to an uncompressed cpio archive.
+# They must be put into a /kernel/firmware/acpi/overlay directory inside the
+# cpio archive.
+# The uncompressed cpio archive must be the first.
+# Other, typically compressed cpio archives, must be
+# concatenated on top of the uncompressed one.
+mkdir -p kernel/firmware/acpi
+cp ssdt.aml kernel/firmware/acpi
+
+# Create the uncompressed cpio archive and concatenate the original initrd
+# on top:
+find kernel | cpio -H newc --create > /boot/instrumented_initrd
+cat /boot/initrd >>/boot/instrumented_initrd
+
diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 891c42d..5e0d076 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -37,9 +37,14 @@
#include <acpi/apei.h>
#include <linux/dmi.h>
#include <linux/suspend.h>
+#include <linux/initrd.h>
+#include <linux/earlycpio.h>
#include "internal.h"
+#undef pr_fmt
+#define pr_fmt(fmt) "ACPI: " fmt
+
#define _COMPONENT ACPI_BUS_COMPONENT
ACPI_MODULE_NAME("bus");
@@ -863,6 +868,62 @@ static int __init acpi_bus_init_irq(void)
return 0;
}
+void __init acpi_load_initrd_ssdts(void)
+{
+ void *data = (void *)initrd_start;
+ int size = initrd_end - initrd_start;
+ const char *path = "kernel/firmware/acpi/overlay";
+ long offset = 0;
+ struct cpio_data file;
+ struct acpi_table_header *header;
+ void *table;
+ acpi_status status;
+
+ while (true) {
+ file = find_cpio_data(path, data, size, &offset);
+ if (!file.data)
+ break;
+
+ data += offset;
+ size -= offset;
+
+ if (file.size < sizeof(struct acpi_table_header)) {
+ pr_err("initrd table smaller than ACPI header [%s%s]\n",
+ path, file.name);
+ continue;
+ }
+
+ header = file.data;
+
+ if (file.size != header->length) {
+ pr_err("initrd file / table length mismatch [%s%s]\n",
+ path, file.name);
+ continue;
+ }
+
+ if (memcmp(header->signature, ACPI_SIG_SSDT, 4)) {
+ pr_warn("skipping non-SSDT initrd table [%s%s]\n",
+ path, file.name);
+ continue;
+ }
+
+ table = kmemdup(file.data, file.size, GFP_KERNEL);
+ if (!table)
+ continue;
+
+ status = acpi_install_table((uintptr_t)table, 0);
+ if (ACPI_FAILURE(status)) {
+ pr_err("failed to install SSDT from initrd [%s%s]\n",
+ path, file.name);
+ kfree(table);
+ }
+
+ pr_info("installed SSDT table found in initrd [%s%s][0x%x]\n",
+ path, file.name, header->length);
+ add_taint(TAINT_OVERLAY_ACPI_TABLE, LOCKDEP_STILL_OK);
+ }
+}
+
/**
* acpi_early_init - Initialize ACPICA and populate the ACPI namespace.
*
@@ -911,6 +972,8 @@ void __init acpi_early_init(void)
goto error0;
}
+ acpi_load_initrd_ssdts();
+
status = acpi_load_tables();
if (ACPI_FAILURE(status)) {
printk(KERN_ERR PREFIX
--
1.9.1
--
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