[PATCH v3 2/2] i2c, i2c_imc: Add DIMM bus code

From: Andy Lutomirski
Date: Thu Apr 28 2016 - 21:04:13 EST

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Add i2c_scan_dimm_bus to declare that a particular i2c_adapter
contains DIMMs. This will probe (and autoload modules!) for useful
SMBUS devices that live on DIMMs. i2c_imc calls it.

As more SMBUS-addressable DIMM components become supported, this
code can be extended to probe for them.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
drivers/i2c/busses/Kconfig | 5 ++
drivers/i2c/busses/Makefile | 4 ++
drivers/i2c/busses/dimm-bus.c | 107 ++++++++++++++++++++++++++++++++++++++++++
drivers/i2c/busses/i2c-imc.c | 3 ++
include/linux/i2c/dimm-bus.h | 20 ++++++++
5 files changed, 139 insertions(+)
create mode 100644 drivers/i2c/busses/dimm-bus.c
create mode 100644 include/linux/i2c/dimm-bus.h

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 3c05de897566..10aa87872408 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -152,9 +152,14 @@ config I2C_ISMT
This driver can also be built as a module. If so, the module will be
called i2c-ismt.

+config I2C_DIMM_BUS
+ tristate
+ default n
+
config I2C_IMC
tristate "Intel iMC (LGA 2011) SMBus Controller"
depends on PCI && X86
+ select I2C_DIMM_BUS
help
If you say yes to this option, support will be included for the Intel
Integrated Memory Controller SMBus host controller interface. This
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index ab3cdf1b3ca1..093591935bc8 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -25,6 +25,10 @@ obj-$(CONFIG_I2C_SIS96X) += i2c-sis96x.o
obj-$(CONFIG_I2C_VIA) += i2c-via.o
obj-$(CONFIG_I2C_VIAPRO) += i2c-viapro.o

+# DIMM busses
+obj-$(CONFIG_I2C_DIMM_BUS) += dimm-bus.o
+obj-$(CONFIG_I2C_IMC) += i2c-imc.o
+
# Mac SMBus host controller drivers
obj-$(CONFIG_I2C_HYDRA) += i2c-hydra.o
obj-$(CONFIG_I2C_POWERMAC) += i2c-powermac.o
diff --git a/drivers/i2c/busses/dimm-bus.c b/drivers/i2c/busses/dimm-bus.c
new file mode 100644
index 000000000000..d41c1095c093
--- /dev/null
+++ b/drivers/i2c/busses/dimm-bus.c
@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2013-2016 Andrew Lutomirski <luto@xxxxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/i2c.h>
+#include <linux/bug.h>
+#include <linux/module.h>
+#include <linux/i2c/dimm-bus.h>
+
+static bool probe_addr(struct i2c_adapter *adapter, int addr)
+{
+ /*
+ * So far, all known devices that live on DIMMs can be safely
+ * and reliably detected by trying to read a byte at address
+ * zero. (The exception is the SPD write protection control,
+ * which can't be probed and requires special hardware and/or
+ * quick writes to access, and has no driver.)
+ */
+ union i2c_smbus_data dummy;
+
+ return i2c_smbus_xfer(adapter, addr, 0, I2C_SMBUS_READ, 0,
+ I2C_SMBUS_BYTE_DATA, &dummy) >= 0;
+}
+
+/**
+ * i2c_scan_dimm_bus() - Scans an SMBUS segment known to contain DIMMs
+ * @adapter: The SMBUS adapter to scan
+ *
+ * This function tells the DIMM-bus code that the adapter is known to
+ * contain DIMMs. i2c_scan_dimm_bus will probe for devices known to
+ * live on DIMMs.
+ *
+ * Do NOT call this function on general-purpose system SMBUS segments
+ * unless you know that the only things on the bus are DIMMs.
+ * Otherwise is it very likely to mis-identify other things on the
+ * bus.
+ *
+ * Callers are advised not to set adapter->class = I2C_CLASS_SPD to
+ * avoid having two separate mechanisms trying to automatically claim
+ * devices on the bus.
+ */
+void i2c_scan_dimm_bus(struct i2c_adapter *adapter)
+{
+ struct i2c_board_info info = {};
+ int slot;
+
+ /*
+ * We probe with "read byte data". If any DIMM SMBUS driver can't
+ * support that access type, this function should be updated.
+ */
+ if (WARN_ON(!i2c_check_functionality(adapter,
+ I2C_FUNC_SMBUS_READ_BYTE_DATA)))
+ return;
+
+ /*
+ * Addresses on DIMMs use the three low bits to identify the slot
+ * and the four high bits to identify the device type. Known
+ * devices are:
+ *
+ * - 0x50 - 0x57: SPD (Serial Presence Detect) EEPROM
+ * - 0x30 - 0x37: SPD WP control -- not easy to probe
+ * - 0x18 - 0x1f: TSOD (Temperature Sensor on DIMM)
+ *
+ * There's no point in trying to probe the SPD WP control: we'd
+ * want to probe using quick reads, which i2c-imc doesn't
+ * support, we don't have a driver for it, we can't really use
+ * it without special hardware (it's not a normal i2c slave --
+ * see the JEDEC docs), and using it risks bricking the DIMM
+ * it's on anyway.
+ *
+ * NB: There's no need to save the return value from
+ * i2c_new_device, as the core code will unregister it for us
+ * when the adapter is removed. If users want to bind a
+ * different driver, nothing stops them from unbinding the
+ * drivers we request here.
+ */
+ for (slot = 0; slot < 8; slot++) {
+ /* If there's no SPD, then assume there's no DIMM here. */
+ if (!probe_addr(adapter, 0x50 | slot))
+ continue;
+
+ strcpy(info.type, "spd");
+ info.addr = 0x50 | slot;
+ i2c_new_device(adapter, &info);
+
+ if (probe_addr(adapter, 0x18 | slot)) {
+ /* This is a temperature sensor. */
+ strcpy(info.type, "jc42");
+ info.addr = 0x18 | slot;
+ i2c_new_device(adapter, &info);
+ }
+ }
+}
+EXPORT_SYMBOL(i2c_scan_dimm_bus);
+
+MODULE_AUTHOR("Andrew Lutomirski <luto@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("i2c DIMM bus support");
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/i2c/busses/i2c-imc.c b/drivers/i2c/busses/i2c-imc.c
index ace93bb1adb2..57cc44879061 100644
--- a/drivers/i2c/busses/i2c-imc.c
+++ b/drivers/i2c/busses/i2c-imc.c
@@ -19,6 +19,7 @@
#include <linux/pci.h>
#include <linux/ratelimit.h>
#include <linux/i2c.h>
+#include <linux/i2c/dimm-bus.h>

/*
* The datasheet can be found here, for example:
@@ -416,6 +417,8 @@ static int imc_init_channel(struct imc_priv *priv, int i, int socket)
return err;
}

+ i2c_scan_dimm_bus(&ch->adapter);
+
return 0;
}

diff --git a/include/linux/i2c/dimm-bus.h b/include/linux/i2c/dimm-bus.h
new file mode 100644
index 000000000000..21559058e034
--- /dev/null
+++ b/include/linux/i2c/dimm-bus.h
@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2013-2016 Andrew Lutomirski <luto@xxxxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _I2C_DIMM_BUS
+#define _I2C_DIMM_BUS
+
+struct i2c_adapter;
+void i2c_scan_dimm_bus(struct i2c_adapter *adapter);
+
+#endif /* _I2C_DIMM_BUS */
--
2.5.5

Next message: Jason Wang: "Re: [RFC PATCH V2 2/2] vhost: device IOTLB API"
Previous message: Andy Lutomirski: "[PATCH v3 1/2] i2c_imc: New driver for Intel's iMC, found on LGA2011 SNB chips"
In reply to: Andy Lutomirski: "[PATCH v3 1/2] i2c_imc: New driver for Intel's iMC, found on LGA2011 SNB chips"
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