[PATCH v4] platform/chrome: cros_ec_lpc: Choose Microchip EC at runtime

From: Enric Balletbo i Serra
Date: Fri Jun 14 2019 - 00:39:13 EST

On many boards, communication between the kernel and the Embedded
Controller happens over an LPC bus. In these cases, the kernel config
CONFIG_CROS_EC_LPC is enabled. Some of these LPC boards contain a
Microchip Embedded Controller (MEC) that is different from the regular
EC. On these devices, the same LPC bus is used, but the protocol is
a little different. In these cases, the CONFIG_CROS_EC_LPC_MEC kernel
config is enabled. Currently, the kernel decides at compile-time whether
or not to use the MEC variant, and, when that kernel option is selected
it breaks the other boards. We would like a kind of runtime detection to
avoid this.

This patch adds that detection mechanism by probing the protocol at
runtime, first we assume that a MEC variant is connected, and if the
protocol fails it fallbacks to the regular EC. This adds a bit of
overload because we try to read twice on those LPC boards that doesn't
contain a MEC variant, but is a better solution than having to select the
EC variant at compile-time.

While here also fix the alignment in Kconfig file for this config option
replacing the spaces by tabs.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
Reviewed-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
Tested-by: Nick Crews <ncrews@xxxxxxxxxxxx>
---
Hi,

This is another attempt to solve the issue to be able to select at
runtime the CrOS MEC variant. My first thought was check for a device
ID, the MEC1322 has a register that contains the device ID, however I
am not sure if we can read that register from the host without
modifying the firmware. Also, I am not sure if the MEC1322 is the only
device used that supports that LPC protocol variant, so I ended with a
more easy solution, check if the protocol fails or not. Some background
on this issue can be found [1] and [2]

The patch has been tested on:
- Acer Chromebook R11 (Cyan - MEC variant)
- Pixel Chromebook 2015 (Samus - non-MEC variant)
- Dell Chromebook 11 (Wolf - non-MEC variant)
- Toshiba Chromebook (Leon - non-MEC variant)

Best regards,
Enric

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=932626
[2] https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/1474254

Changes in v4:
- Change the logic to test the protocols as suggested by Nick Crews.
- Add the proper cros_ec_lpc_mec.h include. (Nick Crews)
- Fix some const and missing casts. (Nick Crews)
- Clean up related doc-strings. (Nick Crews)

Changes in v3:
- Kconfig: Split across multiple lines to keep it under 80 characters.
- Improve kernel-doc as suggested by Nick Crews.
- Convert msg in write function to const.
- Add rb and tb tags.

Changes in v2:
- Remove global bool to indicate the kind of variant as suggested by Ezequiel.
- Create an internal operations struct to allow different variants.

drivers/platform/chrome/Kconfig | 29 +++------
drivers/platform/chrome/Makefile | 2 +-
drivers/platform/chrome/cros_ec_lpc.c | 78 ++++++++++++++++-------
drivers/platform/chrome/cros_ec_lpc_mec.h | 14 ++++
drivers/platform/chrome/cros_ec_lpc_reg.c | 41 ++++--------
drivers/platform/chrome/cros_ec_lpc_reg.h | 23 +++----
drivers/platform/chrome/wilco_ec/Kconfig | 2 +-
7 files changed, 98 insertions(+), 91 deletions(-)

diff --git a/drivers/platform/chrome/Kconfig b/drivers/platform/chrome/Kconfig
index 2826f7136f65..453e69733842 100644
--- a/drivers/platform/chrome/Kconfig
+++ b/drivers/platform/chrome/Kconfig
@@ -83,28 +83,17 @@ config CROS_EC_SPI
'pre-amble' bytes before the response actually starts.

config CROS_EC_LPC
- tristate "ChromeOS Embedded Controller (LPC)"
- depends on MFD_CROS_EC && ACPI && (X86 || COMPILE_TEST)
- help
- If you say Y here, you get support for talking to the ChromeOS EC
- over an LPC bus. This uses a simple byte-level protocol with a
- checksum. This is used for userspace access only. The kernel
- typically has its own communication methods.
-
- To compile this driver as a module, choose M here: the
- module will be called cros_ec_lpc.
-
-config CROS_EC_LPC_MEC
- bool "ChromeOS Embedded Controller LPC Microchip EC (MEC) variant"
- depends on CROS_EC_LPC
- default n
+ tristate "ChromeOS Embedded Controller (LPC)"
+ depends on MFD_CROS_EC && ACPI && (X86 || COMPILE_TEST)
help
- If you say Y here, a variant LPC protocol for the Microchip EC
- will be used. Note that this variant is not backward compatible
- with non-Microchip ECs.
+ If you say Y here, you get support for talking to the ChromeOS EC
+ over an LPC bus, including the LPC Microchip EC (MEC) variant.
+ This uses a simple byte-level protocol with a checksum. This is
+ used for userspace access only. The kernel typically has its own
+ communication methods.

- If you have a ChromeOS Embedded Controller Microchip EC variant
- choose Y here.
+ To compile this driver as a module, choose M here: the
+ module will be called cros_ec_lpcs.

config CROS_EC_PROTO
bool
diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
index 1b2f1dcfcd5c..da9aa08d9fa6 100644
--- a/drivers/platform/chrome/Makefile
+++ b/drivers/platform/chrome/Makefile
@@ -10,7 +10,7 @@ obj-$(CONFIG_CROS_EC_I2C) += cros_ec_i2c.o
obj-$(CONFIG_CROS_EC_RPMSG) += cros_ec_rpmsg.o
obj-$(CONFIG_CROS_EC_SPI) += cros_ec_spi.o
cros_ec_lpcs-objs := cros_ec_lpc.o cros_ec_lpc_reg.o
-cros_ec_lpcs-$(CONFIG_CROS_EC_LPC_MEC) += cros_ec_lpc_mec.o
+cros_ec_lpcs-objs += cros_ec_lpc_mec.o
obj-$(CONFIG_CROS_EC_LPC) += cros_ec_lpcs.o
obj-$(CONFIG_CROS_EC_PROTO) += cros_ec_proto.o cros_ec_trace.o
obj-$(CONFIG_CROS_KBD_LED_BACKLIGHT) += cros_kbd_led_backlight.o
diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
index c9c240fbe7c6..d6ba6b464abc 100644
--- a/drivers/platform/chrome/cros_ec_lpc.c
+++ b/drivers/platform/chrome/cros_ec_lpc.c
@@ -23,11 +23,29 @@
#include <linux/printk.h>
#include <linux/suspend.h>

+#include "cros_ec_lpc_mec.h"
#include "cros_ec_lpc_reg.h"

#define DRV_NAME "cros_ec_lpcs"
#define ACPI_DRV_NAME "GOOG0004"

+/**
+ * struct lpc_driver_ops - LPC driver operations
+ * @read: Copy length bytes from EC address offset into buffer dest. Returns
+ * the 8-bit checksum of all bytes read.
+ * @write: Copy length bytes from buffer msg into EC address offset. Returns
+ * the 8-bit checksum of all bytes written.
+ */
+struct lpc_driver_ops {
+ u8 (*read)(unsigned int offset, unsigned int length, u8 *dest);
+ u8 (*write)(unsigned int offset, unsigned int length, const u8 *msg);
+};
+
+static struct lpc_driver_ops cros_ec_lpc_ops = {
+ .read = cros_ec_lpc_mec_read_bytes,
+ .write = cros_ec_lpc_mec_write_bytes,
+};
+
/* True if ACPI device is present */
static bool cros_ec_lpc_acpi_device_found;

@@ -38,7 +56,7 @@ static int ec_response_timed_out(void)

usleep_range(200, 300);
do {
- if (!(cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_CMD, 1, &data) &
+ if (!(cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_CMD, 1, &data) &
EC_LPC_STATUS_BUSY_MASK))
return 0;
usleep_range(100, 200);
@@ -58,11 +76,11 @@ static int cros_ec_pkt_xfer_lpc(struct cros_ec_device *ec,
ret = cros_ec_prepare_tx(ec, msg);

/* Write buffer */
- cros_ec_lpc_write_bytes(EC_LPC_ADDR_HOST_PACKET, ret, ec->dout);
+ cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_PACKET, ret, ec->dout);

/* Here we go */
sum = EC_COMMAND_PROTOCOL_3;
- cros_ec_lpc_write_bytes(EC_LPC_ADDR_HOST_CMD, 1, &sum);
+ cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_CMD, 1, &sum);

if (ec_response_timed_out()) {
dev_warn(ec->dev, "EC responsed timed out\n");
@@ -71,15 +89,15 @@ static int cros_ec_pkt_xfer_lpc(struct cros_ec_device *ec,
}

/* Check result */
- msg->result = cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_DATA, 1, &sum);
+ msg->result = cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_DATA, 1, &sum);
ret = cros_ec_check_result(ec, msg);
if (ret)
goto done;

/* Read back response */
dout = (u8 *)&response;
- sum = cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_PACKET, sizeof(response),
- dout);
+ sum = cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_PACKET, sizeof(response),
+ dout);

msg->result = response.result;

@@ -92,9 +110,9 @@ static int cros_ec_pkt_xfer_lpc(struct cros_ec_device *ec,
}

/* Read response and process checksum */
- sum += cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_PACKET +
- sizeof(response), response.data_len,
- msg->data);
+ sum += cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_PACKET +
+ sizeof(response), response.data_len,
+ msg->data);

if (sum) {
dev_err(ec->dev,
@@ -134,17 +152,17 @@ static int cros_ec_cmd_xfer_lpc(struct cros_ec_device *ec,
sum = msg->command + args.flags + args.command_version + args.data_size;

/* Copy data and update checksum */
- sum += cros_ec_lpc_write_bytes(EC_LPC_ADDR_HOST_PARAM, msg->outsize,
- msg->data);
+ sum += cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_PARAM, msg->outsize,
+ msg->data);

/* Finalize checksum and write args */
args.checksum = sum;
- cros_ec_lpc_write_bytes(EC_LPC_ADDR_HOST_ARGS, sizeof(args),
- (u8 *)&args);
+ cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_ARGS, sizeof(args),
+ (u8 *)&args);

/* Here we go */
sum = msg->command;
- cros_ec_lpc_write_bytes(EC_LPC_ADDR_HOST_CMD, 1, &sum);
+ cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_CMD, 1, &sum);

if (ec_response_timed_out()) {
dev_warn(ec->dev, "EC responsed timed out\n");
@@ -153,14 +171,13 @@ static int cros_ec_cmd_xfer_lpc(struct cros_ec_device *ec,
}

/* Check result */
- msg->result = cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_DATA, 1, &sum);
+ msg->result = cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_DATA, 1, &sum);
ret = cros_ec_check_result(ec, msg);
if (ret)
goto done;

/* Read back args */
- cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_ARGS, sizeof(args),
- (u8 *)&args);
+ cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_ARGS, sizeof(args), (u8 *)&args);

if (args.data_size > msg->insize) {
dev_err(ec->dev,
@@ -174,8 +191,8 @@ static int cros_ec_cmd_xfer_lpc(struct cros_ec_device *ec,
sum = msg->command + args.flags + args.command_version + args.data_size;

/* Read response and update checksum */
- sum += cros_ec_lpc_read_bytes(EC_LPC_ADDR_HOST_PARAM, args.data_size,
- msg->data);
+ sum += cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_PARAM, args.data_size,
+ msg->data);

/* Verify checksum */
if (args.checksum != sum) {
@@ -205,13 +222,13 @@ static int cros_ec_lpc_readmem(struct cros_ec_device *ec, unsigned int offset,

/* fixed length */
if (bytes) {
- cros_ec_lpc_read_bytes(EC_LPC_ADDR_MEMMAP + offset, bytes, s);
+ cros_ec_lpc_ops.read(EC_LPC_ADDR_MEMMAP + offset, bytes, s);
return bytes;
}

/* string */
for (; i < EC_MEMMAP_SIZE; i++, s++) {
- cros_ec_lpc_read_bytes(EC_LPC_ADDR_MEMMAP + i, 1, s);
+ cros_ec_lpc_ops.read(EC_LPC_ADDR_MEMMAP + i, 1, s);
cnt++;
if (!*s)
break;
@@ -248,10 +265,23 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
return -EBUSY;
}

- cros_ec_lpc_read_bytes(EC_LPC_ADDR_MEMMAP + EC_MEMMAP_ID, 2, buf);
+ /*
+ * Read the mapped ID twice, the first one is assuming the
+ * EC is a Microchip Embedded Controller (MEC) variant, if the
+ * protocol fails, fallback to the non MEC variant and try to
+ * read again the ID.
+ */
+ cros_ec_lpc_ops.read(EC_LPC_ADDR_MEMMAP + EC_MEMMAP_ID, 2, buf);
if (buf[0] != 'E' || buf[1] != 'C') {
- dev_err(dev, "EC ID not detected\n");
- return -ENODEV;
+ /* Re-assign read/write operations for the non MEC variant */
+ cros_ec_lpc_ops.read = cros_ec_lpc_read_bytes;
+ cros_ec_lpc_ops.write = cros_ec_lpc_write_bytes;
+ cros_ec_lpc_ops.read(EC_LPC_ADDR_MEMMAP + EC_MEMMAP_ID, 2,
+ buf);
+ if (buf[0] != 'E' || buf[1] != 'C') {
+ dev_err(dev, "EC ID not detected\n");
+ return -ENODEV;
+ }
}

if (!devm_request_region(dev, EC_HOST_CMD_REGION0,
diff --git a/drivers/platform/chrome/cros_ec_lpc_mec.h b/drivers/platform/chrome/cros_ec_lpc_mec.h
index aa1018f6b0f2..fcaabdbb5e62 100644
--- a/drivers/platform/chrome/cros_ec_lpc_mec.h
+++ b/drivers/platform/chrome/cros_ec_lpc_mec.h
@@ -76,4 +76,18 @@ int cros_ec_lpc_mec_in_range(unsigned int offset, unsigned int length);
u8 cros_ec_lpc_io_bytes_mec(enum cros_ec_lpc_mec_io_type io_type,
unsigned int offset, unsigned int length, u8 *buf);

+/*
+ * An instance of the read function of struct lpc_driver_ops, used for the
+ * MEC variant of LPC EC.
+ */
+u8 cros_ec_lpc_mec_read_bytes(unsigned int offset, unsigned int length,
+ u8 *dest);
+
+/*
+ * An instance of the write function of struct lpc_driver_ops, used for the
+ * MEC variant of LPC EC.
+ */
+u8 cros_ec_lpc_mec_write_bytes(unsigned int offset, unsigned int length,
+ const u8 *msg);
+
#endif /* __CROS_EC_LPC_MEC_H */
diff --git a/drivers/platform/chrome/cros_ec_lpc_reg.c b/drivers/platform/chrome/cros_ec_lpc_reg.c
index 0f5cd0ac8b49..3bfeb5ad59ba 100644
--- a/drivers/platform/chrome/cros_ec_lpc_reg.c
+++ b/drivers/platform/chrome/cros_ec_lpc_reg.c
@@ -9,7 +9,7 @@

#include "cros_ec_lpc_mec.h"

-static u8 lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
+u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
{
int i;
int sum = 0;
@@ -23,7 +23,8 @@ static u8 lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
return sum;
}

-static u8 lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
+u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
+ const u8 *msg)
{
int i;
int sum = 0;
@@ -37,9 +38,9 @@ static u8 lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
return sum;
}

-#ifdef CONFIG_CROS_EC_LPC_MEC

-u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
+u8 cros_ec_lpc_mec_read_bytes(unsigned int offset, unsigned int length,
+ u8 *dest)
{
int in_range = cros_ec_lpc_mec_in_range(offset, length);

@@ -50,10 +51,12 @@ u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
cros_ec_lpc_io_bytes_mec(MEC_IO_READ,
offset - EC_HOST_CMD_REGION0,
length, dest) :
- lpc_read_bytes(offset, length, dest);
+ cros_ec_lpc_read_bytes(offset, length, dest);
+
}

-u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
+u8 cros_ec_lpc_mec_write_bytes(unsigned int offset, unsigned int length,
+ const u8 *msg)
{
int in_range = cros_ec_lpc_mec_in_range(offset, length);

@@ -63,8 +66,8 @@ u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
return in_range ?
cros_ec_lpc_io_bytes_mec(MEC_IO_WRITE,
offset - EC_HOST_CMD_REGION0,
- length, msg) :
- lpc_write_bytes(offset, length, msg);
+ length, (u8 *)msg) :
+ cros_ec_lpc_write_bytes(offset, length, msg);
}

void cros_ec_lpc_reg_init(void)
@@ -77,25 +80,3 @@ void cros_ec_lpc_reg_destroy(void)
{
cros_ec_lpc_mec_destroy();
}
-
-#else /* CONFIG_CROS_EC_LPC_MEC */
-
-u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
-{
- return lpc_read_bytes(offset, length, dest);
-}
-
-u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
-{
- return lpc_write_bytes(offset, length, msg);
-}
-
-void cros_ec_lpc_reg_init(void)
-{
-}
-
-void cros_ec_lpc_reg_destroy(void)
-{
-}
-
-#endif /* CONFIG_CROS_EC_LPC_MEC */
diff --git a/drivers/platform/chrome/cros_ec_lpc_reg.h b/drivers/platform/chrome/cros_ec_lpc_reg.h
index 416fd2572182..f12115293e47 100644
--- a/drivers/platform/chrome/cros_ec_lpc_reg.h
+++ b/drivers/platform/chrome/cros_ec_lpc_reg.h
@@ -8,25 +8,18 @@
#ifndef __CROS_EC_LPC_REG_H
#define __CROS_EC_LPC_REG_H

-/**
- * cros_ec_lpc_read_bytes - Read bytes from a given LPC-mapped address.
- * Returns 8-bit checksum of all bytes read.
- *
- * @offset: Base read address
- * @length: Number of bytes to read
- * @dest: Destination buffer
+/*
+ * A generic instance of the read function of struct lpc_driver_ops, used for
+ * the LPC EC.
*/
u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest);

-/**
- * cros_ec_lpc_write_bytes - Write bytes to a given LPC-mapped address.
- * Returns 8-bit checksum of all bytes written.
- *
- * @offset: Base write address
- * @length: Number of bytes to write
- * @msg: Write data buffer
+/*
+ * A generic instance of the write function of struct lpc_driver_ops, used for
+ * the LPC EC.
*/
-u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg);
+u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
+ const u8 *msg);

/**
* cros_ec_lpc_reg_init
diff --git a/drivers/platform/chrome/wilco_ec/Kconfig b/drivers/platform/chrome/wilco_ec/Kconfig
index fd29cbfd3d5d..c63ff2508409 100644
--- a/drivers/platform/chrome/wilco_ec/Kconfig
+++ b/drivers/platform/chrome/wilco_ec/Kconfig
@@ -1,7 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
config WILCO_EC
tristate "ChromeOS Wilco Embedded Controller"
- depends on ACPI && X86 && CROS_EC_LPC && CROS_EC_LPC_MEC
+ depends on ACPI && X86 && CROS_EC_LPC
help
If you say Y here, you get support for talking to the ChromeOS
Wilco EC over an eSPI bus. This uses a simple byte-level protocol
--
2.20.1