Re: [PATCH v2] platform/chrome: cros_ec_lpc: Choose Microchip EC at runtime

[Ezequiel Garcia]

On Fri, 2019-06-07 at 12:27 +0200, Enric Balletbo i Serra wrote:
> 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>
> ---
> Hi,
> 
> This is the second 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)
> 
> Nick, could you test the patch for Wilco?
> 
> 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 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          |  3 +-
>  drivers/platform/chrome/cros_ec_lpc.c     | 76 ++++++++++++++++-------
>  drivers/platform/chrome/cros_ec_lpc_reg.c | 39 +++---------
>  drivers/platform/chrome/cros_ec_lpc_reg.h | 26 ++++++++
>  drivers/platform/chrome/wilco_ec/Kconfig  |  2 +-
>  6 files changed, 98 insertions(+), 77 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..d6416411888f 100644
> --- a/drivers/platform/chrome/Makefile
> +++ b/drivers/platform/chrome/Makefile
> @@ -9,8 +9,7 @@ obj-$(CONFIG_CHROMEOS_TBMC)		+= chromeos_tbmc.o
>  obj-$(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-$(CONFIG_CROS_EC_LPC_MEC)	+= cros_ec_lpc_mec.o
> +cros_ec_lpcs-objs			:= cros_ec_lpc.o cros_ec_lpc_reg.o cros_ec_lpc_mec.o
>  obj-$(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..91cb4dd34764 100644
> --- a/drivers/platform/chrome/cros_ec_lpc.c
> +++ b/drivers/platform/chrome/cros_ec_lpc.c
> @@ -28,6 +28,22 @@
>  #define DRV_NAME "cros_ec_lpcs"
>  #define ACPI_DRV_NAME "GOOG0004"
>  
> +/**
> + * struct lpc_ops - LPC driver methods
> + *
> + * @read: Read bytes from a given LPC-mapped address.
> + * @write: Write bytes to a given LPC-mapped address.
> + */
> +struct lpc_ops {
> +	u8	(*read)(unsigned int offset, unsigned int length, u8 *dest);
> +	u8	(*write)(unsigned int offset, unsigned int length, u8 *msg);
> +};
> +
> +static struct lpc_ops cros_ec_lpc_ops = {
> +	.read	= cros_ec_lpc_mec_read_bytes,
> +	.write	= cros_ec_lpc_mec_write_bytes,
> +};
> +

While this is better than a global boolean, it's still not
per-device.

I guess it's not an issue given you typically (always?)
have one cros-ec device per platform.

However, I'm still wondering if it's not better to make it
per-device (as the bus is per-device?).
 
>  /* True if ACPI device is present */
>  static bool cros_ec_lpc_acpi_device_found;
>  
> @@ -38,7 +54,7 @@ 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 +74,11 @@ 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 +87,15 @@ 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 +108,9 @@ 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 +150,17 @@ 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 +169,13 @@ 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 +189,8 @@ 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 +220,13 @@ 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 +263,23 @@ 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_mec_read_bytes(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;
> +		cros_ec_lpc_read_bytes(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;
>  	}
>  
>  	if (!devm_request_region(dev, EC_HOST_CMD_REGION0,
> diff --git a/drivers/platform/chrome/cros_ec_lpc_reg.c b/drivers/platform/chrome/cros_ec_lpc_reg.c
> index 0f5cd0ac8b49..389d3329616f 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 +23,7 @@ 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, u8 *msg)
>  {
>  	int i;
>  	int sum = 0;
> @@ -37,9 +37,8 @@ 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 +49,12 @@ 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,
> +			       u8 *msg)
>  {
>  	int in_range = cros_ec_lpc_mec_in_range(offset, length);
>  
> @@ -64,7 +65,7 @@ u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
>  		cros_ec_lpc_io_bytes_mec(MEC_IO_WRITE,
>  					 offset - EC_HOST_CMD_REGION0,
>  					 length, msg) :
> -		lpc_write_bytes(offset, length, msg);
> +		cros_ec_lpc_write_bytes(offset, length, msg);
>  }
>  
>  void cros_ec_lpc_reg_init(void)
> @@ -77,25 +78,3 @@ 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..e8d53fb8a2bc 100644
> --- a/drivers/platform/chrome/cros_ec_lpc_reg.h
> +++ b/drivers/platform/chrome/cros_ec_lpc_reg.h
> @@ -28,6 +28,32 @@ u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest);
>   */
>  u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg);
>  
> +/**
> + * cros_ec_lpc_mec_read_bytes() - Read bytes from a given LPC-mapped address.
> + * @offset: Base read address
> + * @length: Number of bytes to read
> + * @dest: Destination buffer
> + *
> + * This function is for the MEC (Microchip Embedded Controller) variant.
> + *
> + * Return: 8-bit checksum of all bytes read.
> + */
> +u8 cros_ec_lpc_mec_read_bytes(unsigned int offset, unsigned int length,
> +			      u8 *dest);
> +
> +/**
> + * cros_ec_lpc_mec_write_bytes - Write bytes to a given LPC-mapped address.
> + * @offset: Base write address
> + * @length: Number of bytes to write
> + * @msg: Write data buffer
> + *
> + * This function is for the MEC (Microchip Embedded Controller) variant.
> + *
> + * Return: 8-bit checksum of all bytes written.
> + */
> +u8 cros_ec_lpc_mec_write_bytes(unsigned int offset, unsigned int length,
> +			       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
> 
>