Re: [PATCH v3 6/7] i2c: ChromeOS EC tunnel driver

From: Lee Jones
Date: Tue May 20 2014 - 04:47:26 EST

On Wed, 30 Apr 2014, Doug Anderson wrote:

> On ARM Chromebooks we have a few devices that are accessed by both the
> AP (the main "Application Processor") and the EC (the Embedded
> Controller). These are:
> * The battery (sbs-battery).
> * The power management unit tps65090.
>
> On the original Samsung ARM Chromebook these devices were on an I2C
> bus that was shared between the AP and the EC and arbitrated using
> some extranal GPIOs (see i2c-arb-gpio-challenge).
>
> The original arbitration scheme worked well enough but had some
> downsides:
> * It was nonstandard (not using standard I2C multimaster)
> * It only worked if the EC-AP communication was I2C
> * It was relatively hard to debug problems (hard to tell if i2c issues
> were caused by the EC, the AP, or some device on the bus).
>
> On the HP Chromebook 11 the design was changed to:
> * The AP/EC comms were still i2c, but the battery/tps65090 were no
> longer on the bus used for AP/EC communication. The battery was
> exposed to the AP through a limited i2c tunnel and tps65090 was
> exposed to the AP through a custom Linux driver.
>
> On the Samsung ARM Chromebook 2 the scheme is changed yet again, now:
> * The AP/EC comms are now using SPI for faster speeds.
> * The EC's i2c bus is exposed to the AP through a full i2c tunnel.
>
> The upstream "tegra124-venice2" uses the same scheme as the Samsung
> ARM Chromebook 2, though it has a different set of components on the
> other side of the bus.
>
> This driver supports the scheme used by the Samsung ARM Chromebook 2.
> Future patches to this driver could add support for the battery tunnel
> on the HP Chromebook 11 (and perhaps could even be used to access
> tps65090 on the HP Chromebook 11 instead of using a special driver,
> but I haven't researched that enough).
>
> Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>
> Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> ---
> Changes in v3:
> - Separate out packet sizing from packet stuffing.
> - Get rid of useless dev_dbg.
> - Check command_sendrecv against NULL.
> - Don't check np against NULL.
> - Get rid of useless error on memory alloc fail.
> - Get rid of useless platform_set_drvdata(dev, NULL);
>
> Changes in v2:
> - Update tunnel binding as per swarren
>
> .../devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt | 39 +++
> drivers/i2c/busses/Kconfig | 9 +
> drivers/i2c/busses/Makefile | 1 +
> drivers/i2c/busses/i2c-cros-ec-tunnel.c | 318 +++++++++++++++++++++
> drivers/mfd/cros_ec.c | 5 +
> 5 files changed, 372 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt
> create mode 100644 drivers/i2c/busses/i2c-cros-ec-tunnel.c

Applied, thanks.

> diff --git a/Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt b/Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt
> new file mode 100644
> index 0000000..898f030
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt
> @@ -0,0 +1,39 @@
> +I2C bus that tunnels through the ChromeOS EC (cros-ec)
> +======================================================
> +On some ChromeOS board designs we've got a connection to the EC (embedded
> +controller) but no direct connection to some devices on the other side of
> +the EC (like a battery and PMIC). To get access to those devices we need
> +to tunnel our i2c commands through the EC.
> +
> +The node for this device should be under a cros-ec node like google,cros-ec-spi
> +or google,cros-ec-i2c.
> +
> +
> +Required properties:
> +- compatible: google,cros-ec-i2c-tunnel
> +- google,remote-bus: The EC bus we'd like to talk to.
> +
> +Optional child nodes:
> +- One node per I2C device connected to the tunnelled I2C bus.
> +
> +
> +Example:
> + cros-ec@0 {
> + compatible = "google,cros-ec-spi";
> +
> + ...
> +
> + i2c-tunnel {
> + compatible = "google,cros-ec-i2c-tunnel";
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + google,remote-bus = <0>;
> +
> + battery: sbs-battery@b {
> + compatible = "sbs,sbs-battery";
> + reg = <0xb>;
> + sbs,poll-retry-count = <1>;
> + };
> + };
> + }
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index c94db1c..9a0a6cc 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -993,6 +993,15 @@ config I2C_SIBYTE
> help
> Supports the SiByte SOC on-chip I2C interfaces (2 channels).
>
> +config I2C_CROS_EC_TUNNEL
> + tristate "ChromeOS EC tunnel I2C bus"
> + depends on MFD_CROS_EC
> + help
> + If you say yes here you get an I2C bus that will tunnel i2c commands
> + through to the other side of the ChromeOS EC to the i2c bus
> + connected there. This will work whatever the interface used to
> + talk to the EC (SPI, I2C or LPC).
> +
> config SCx200_I2C
> tristate "NatSemi SCx200 I2C using GPIO pins (DEPRECATED)"
> depends on SCx200_GPIO
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index 18d18ff..e110ca9 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -95,6 +95,7 @@ obj-$(CONFIG_I2C_VIPERBOARD) += i2c-viperboard.o
> # Other I2C/SMBus bus drivers
> obj-$(CONFIG_I2C_ACORN) += i2c-acorn.o
> obj-$(CONFIG_I2C_BCM_KONA) += i2c-bcm-kona.o
> +obj-$(CONFIG_I2C_CROS_EC_TUNNEL) += i2c-cros-ec-tunnel.o
> obj-$(CONFIG_I2C_ELEKTOR) += i2c-elektor.o
> obj-$(CONFIG_I2C_PCA_ISA) += i2c-pca-isa.o
> obj-$(CONFIG_I2C_SIBYTE) += i2c-sibyte.o
> diff --git a/drivers/i2c/busses/i2c-cros-ec-tunnel.c b/drivers/i2c/busses/i2c-cros-ec-tunnel.c
> new file mode 100644
> index 0000000..8e7a714
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-cros-ec-tunnel.c
> @@ -0,0 +1,318 @@
> +/*
> + * Copyright (C) 2013 Google, Inc
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * Expose an I2C passthrough to the ChromeOS EC.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +#include <linux/mfd/cros_ec.h>
> +#include <linux/mfd/cros_ec_commands.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +/**
> + * struct ec_i2c_device - Driver data for I2C tunnel
> + *
> + * @dev: Device node
> + * @adap: I2C adapter
> + * @ec: Pointer to EC device
> + * @remote_bus: The EC bus number we tunnel to on the other side.
> + * @request_buf: Buffer for transmitting data; we expect most transfers to fit.
> + * @response_buf: Buffer for receiving data; we expect most transfers to fit.
> + */
> +
> +struct ec_i2c_device {
> + struct device *dev;
> + struct i2c_adapter adap;
> + struct cros_ec_device *ec;
> +
> + u16 remote_bus;
> +
> + u8 request_buf[256];
> + u8 response_buf[256];
> +};
> +
> +/**
> + * ec_i2c_count_message - Count bytes needed for ec_i2c_construct_message
> + *
> + * @i2c_msgs: The i2c messages to read
> + * @num: The number of i2c messages.
> + *
> + * Returns the number of bytes the messages will take up.
> + */
> +static int ec_i2c_count_message(const struct i2c_msg i2c_msgs[], int num)
> +{
> + int i;
> + int size;
> +
> + size = sizeof(struct ec_params_i2c_passthru);
> + size += num * sizeof(struct ec_params_i2c_passthru_msg);
> + for (i = 0; i < num; i++)
> + if (!(i2c_msgs[i].flags & I2C_M_RD))
> + size += i2c_msgs[i].len;
> +
> + return size;
> +}
> +
> +/**
> + * ec_i2c_construct_message - construct a message to go to the EC
> + *
> + * This function effectively stuffs the standard i2c_msg format of Linux into
> + * a format that the EC understands.
> + *
> + * @buf: The buffer to fill. We assume that the buffer is big enough.
> + * @i2c_msgs: The i2c messages to read.
> + * @num: The number of i2c messages.
> + * @bus_num: The remote bus number we want to talk to.
> + *
> + * Returns 0 or a negative error number.
> + */
> +static int ec_i2c_construct_message(u8 *buf, const struct i2c_msg i2c_msgs[],
> + int num, u16 bus_num)
> +{
> + struct ec_params_i2c_passthru *params;
> + u8 *out_data;
> + int i;
> +
> + out_data = buf + sizeof(struct ec_params_i2c_passthru) +
> + num * sizeof(struct ec_params_i2c_passthru_msg);
> +
> + params = (struct ec_params_i2c_passthru *)buf;
> + params->port = bus_num;
> + params->num_msgs = num;
> + for (i = 0; i < num; i++) {
> + const struct i2c_msg *i2c_msg = &i2c_msgs[i];
> + struct ec_params_i2c_passthru_msg *msg = &params->msg[i];
> +
> + msg->len = i2c_msg->len;
> + msg->addr_flags = i2c_msg->addr;
> +
> + if (i2c_msg->flags & I2C_M_TEN)
> + msg->addr_flags |= EC_I2C_FLAG_10BIT;
> +
> + if (i2c_msg->flags & I2C_M_RD) {
> + msg->addr_flags |= EC_I2C_FLAG_READ;
> + } else {
> + memcpy(out_data, i2c_msg->buf, msg->len);
> + out_data += msg->len;
> + }
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * ec_i2c_count_response - Count bytes needed for ec_i2c_parse_response
> + *
> + * @i2c_msgs: The i2c messages to to fill up.
> + * @num: The number of i2c messages expected.
> + *
> + * Returns the number of response bytes expeced.
> + */
> +static int ec_i2c_count_response(struct i2c_msg i2c_msgs[], int num)
> +{
> + int size;
> + int i;
> +
> + size = sizeof(struct ec_response_i2c_passthru);
> + for (i = 0; i < num; i++)
> + if (i2c_msgs[i].flags & I2C_M_RD)
> + size += i2c_msgs[i].len;
> +
> + return size;
> +}
> +
> +/**
> + * ec_i2c_parse_response - Parse a response from the EC
> + *
> + * We'll take the EC's response and copy it back into msgs.
> + *
> + * @buf: The buffer to parse.
> + * @i2c_msgs: The i2c messages to to fill up.
> + * @num: The number of i2c messages; will be modified to include the actual
> + * number received.
> + *
> + * Returns 0 or a negative error number.
> + */
> +static int ec_i2c_parse_response(const u8 *buf, struct i2c_msg i2c_msgs[],
> + int *num)
> +{
> + const struct ec_response_i2c_passthru *resp;
> + const u8 *in_data;
> + int i;
> +
> + in_data = buf + sizeof(struct ec_response_i2c_passthru);
> +
> + resp = (const struct ec_response_i2c_passthru *)buf;
> + if (resp->i2c_status & EC_I2C_STATUS_TIMEOUT)
> + return -ETIMEDOUT;
> + else if (resp->i2c_status & EC_I2C_STATUS_ERROR)
> + return -EREMOTEIO;
> +
> + /* Other side could send us back fewer messages, but not more */
> + if (resp->num_msgs > *num)
> + return -EPROTO;
> + *num = resp->num_msgs;
> +
> + for (i = 0; i < *num; i++) {
> + struct i2c_msg *i2c_msg = &i2c_msgs[i];
> +
> + if (i2c_msgs[i].flags & I2C_M_RD) {
> + memcpy(i2c_msg->buf, in_data, i2c_msg->len);
> + in_data += i2c_msg->len;
> + }
> + }
> +
> + return 0;
> +}
> +
> +static int ec_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg i2c_msgs[],
> + int num)
> +{
> + struct ec_i2c_device *bus = adap->algo_data;
> + struct device *dev = bus->dev;
> + const u16 bus_num = bus->remote_bus;
> + int request_len;
> + int response_len;
> + u8 *request = NULL;
> + u8 *response = NULL;
> + int result;
> +
> + request_len = ec_i2c_count_message(i2c_msgs, num);
> + if (request_len < 0) {
> + dev_warn(dev, "Error constructing message %d\n", request_len);
> + result = request_len;
> + goto exit;
> + }
> + response_len = ec_i2c_count_response(i2c_msgs, num);
> + if (response_len < 0) {
> + /* Unexpected; no errors should come when NULL response */
> + dev_warn(dev, "Error preparing response %d\n", response_len);
> + result = response_len;
> + goto exit;
> + }
> +
> + if (request_len <= ARRAY_SIZE(bus->request_buf)) {
> + request = bus->request_buf;
> + } else {
> + request = kzalloc(request_len, GFP_KERNEL);
> + if (request == NULL) {
> + result = -ENOMEM;
> + goto exit;
> + }
> + }
> + if (response_len <= ARRAY_SIZE(bus->response_buf)) {
> + response = bus->response_buf;
> + } else {
> + response = kzalloc(response_len, GFP_KERNEL);
> + if (response == NULL) {
> + result = -ENOMEM;
> + goto exit;
> + }
> + }
> +
> + ec_i2c_construct_message(request, i2c_msgs, num, bus_num);
> + result = bus->ec->command_sendrecv(bus->ec, EC_CMD_I2C_PASSTHRU,
> + request, request_len,
> + response, response_len);
> + if (result)
> + goto exit;
> +
> + result = ec_i2c_parse_response(response, i2c_msgs, &num);
> + if (result < 0)
> + goto exit;
> +
> + /* Indicate success by saying how many messages were sent */
> + result = num;
> +exit:
> + if (request != bus->request_buf)
> + kfree(request);
> + if (response != bus->response_buf)
> + kfree(response);
> +
> + return result;
> +}
> +
> +static u32 ec_i2c_functionality(struct i2c_adapter *adap)
> +{
> + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
> +}
> +
> +static const struct i2c_algorithm ec_i2c_algorithm = {
> + .master_xfer = ec_i2c_xfer,
> + .functionality = ec_i2c_functionality,
> +};
> +
> +static int ec_i2c_probe(struct platform_device *pdev)
> +{
> + struct device_node *np = pdev->dev.of_node;
> + struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
> + struct device *dev = &pdev->dev;
> + struct ec_i2c_device *bus = NULL;
> + u32 remote_bus;
> + int err;
> +
> + if (!ec->command_sendrecv) {
> + dev_err(dev, "Missing sendrecv\n");
> + return -EINVAL;
> + }
> +
> + bus = devm_kzalloc(dev, sizeof(*bus), GFP_KERNEL);
> + if (bus == NULL)
> + return -ENOMEM;
> +
> + err = of_property_read_u32(np, "google,remote-bus", &remote_bus);
> + if (err) {
> + dev_err(dev, "Couldn't read remote-bus property\n");
> + return err;
> + }
> + bus->remote_bus = remote_bus;
> +
> + bus->ec = ec;
> + bus->dev = dev;
> +
> + bus->adap.owner = THIS_MODULE;
> + strlcpy(bus->adap.name, "cros-ec-i2c-tunnel", sizeof(bus->adap.name));
> + bus->adap.algo = &ec_i2c_algorithm;
> + bus->adap.algo_data = bus;
> + bus->adap.dev.parent = &pdev->dev;
> + bus->adap.dev.of_node = np;
> +
> + err = i2c_add_adapter(&bus->adap);
> + if (err) {
> + dev_err(dev, "cannot register i2c adapter\n");
> + return err;
> + }
> + platform_set_drvdata(pdev, bus);
> +
> + return err;
> +}
> +
> +static int ec_i2c_remove(struct platform_device *dev)
> +{
> + struct ec_i2c_device *bus = platform_get_drvdata(dev);
> +
> + i2c_del_adapter(&bus->adap);
> +
> + return 0;
> +}
> +
> +static struct platform_driver ec_i2c_tunnel_driver = {
> + .probe = ec_i2c_probe,
> + .remove = ec_i2c_remove,
> + .driver = {
> + .name = "cros-ec-i2c-tunnel",
> + },
> +};
> +
> +module_platform_driver(ec_i2c_tunnel_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("EC I2C tunnel driver");
> +MODULE_ALIAS("platform:cros-ec-i2c-tunnel");
> diff --git a/drivers/mfd/cros_ec.c b/drivers/mfd/cros_ec.c
> index c58ab96..61bc909 100644
> --- a/drivers/mfd/cros_ec.c
> +++ b/drivers/mfd/cros_ec.c
> @@ -90,6 +90,11 @@ static const struct mfd_cell cros_devs[] = {
> .id = 1,
> .of_compatible = "google,cros-ec-keyb",
> },
> + {
> + .name = "cros-ec-i2c-tunnel",
> + .id = 2,
> + .of_compatible = "google,cros-ec-i2c-tunnel",
> + },
> };
>
> int cros_ec_register(struct cros_ec_device *ec_dev)

--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org â Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/