Re: [PATCH v5 2/3] platform/chrome: cros_ec_lpc: Choose Microchip EC at runtime

[Nick Crews]

Thanks for the patch Enric!

Just one nit.

On Fri, Jun 14, 2019 at 3:43 PM Enric Balletbo i Serra
<enric.balletbo@xxxxxxxxxxxxx> 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>
> 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 v5:
> - Assign the methods in cros_ec_lpc_probe(), so down there
>   you can see explicitly what the defaults are
>
> 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    | 158 ++++++++++++-----------
>  drivers/platform/chrome/wilco_ec/Kconfig |   2 +-
>  4 files changed, 95 insertions(+), 96 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 e2a250892404..7c831d02c926 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-$(CONFIG_CROS_EC_SPI)              += cros_ec_spi.o
>  cros_ec_lpcs-objs                      := cros_ec_lpc.o
> -cros_ec_lpcs-$(CONFIG_CROS_EC_LPC_MEC) += cros_ec_lpc_mec.o
> +cros_ec_lpcs-objs                      += cros_ec_lpc_mec.o

nit: This can fit on the previous line, so we don't have two lines with the +=.

>  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 00a07c9337b7..b260786cc3cc 100644
> --- a/drivers/platform/chrome/cros_ec_lpc.c
> +++ b/drivers/platform/chrome/cros_ec_lpc.c
> @@ -31,7 +31,26 @@
>  /* True if ACPI device is present */
>  static bool cros_ec_lpc_acpi_device_found;
>
> -static u8 lpc_read_bytes(unsigned int offset, unsigned int length, u8 *dest)
> +/**
> + * 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 = { };
> +
> +/*
> + * A generic instance of the read function of struct lpc_driver_ops, used for
> + * the LPC EC.
> + */
> +static u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length,
> +                                u8 *dest)
>  {
>         int sum = 0;
>         int i;
> @@ -45,7 +64,12 @@ 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)
> +/*
> + * A generic instance of the write function of struct lpc_driver_ops, used for
> + * the LPC EC.
> + */
> +static u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
> +                                 const u8 *msg)
>  {
>         int sum = 0;
>         int i;
> @@ -59,10 +83,12 @@ static u8 lpc_write_bytes(unsigned int offset, unsigned int length, u8 *msg)
>         return sum;
>  }
>
> -#ifdef CONFIG_CROS_EC_LPC_MEC
> -
> -static u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length,
> -                                u8 *dest)
> +/*
> + * An instance of the read function of struct lpc_driver_ops, used for the
> + * MEC variant of LPC EC.
> + */
> +static 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);
>
> @@ -73,11 +99,15 @@ static u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length,
>                 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);
>  }
>
> -static u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
> -                                 u8 *msg)
> +/*
> + * An instance of the write function of struct lpc_driver_ops, used for the
> + * MEC variant of LPC EC.
> + */
> +static 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);
>
> @@ -87,45 +117,10 @@ static u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
>         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);
> -}
> -
> -static void cros_ec_lpc_reg_init(void)
> -{
> -       cros_ec_lpc_mec_init(EC_HOST_CMD_REGION0,
> -                            EC_LPC_ADDR_MEMMAP + EC_MEMMAP_SIZE);
> +                                        length, (u8 *)msg) :
> +               cros_ec_lpc_write_bytes(offset, length, msg);
>  }
>
> -static void cros_ec_lpc_reg_destroy(void)
> -{
> -       cros_ec_lpc_mec_destroy();
> -}
> -
> -#else /* CONFIG_CROS_EC_LPC_MEC */
> -
> -static u8 cros_ec_lpc_read_bytes(unsigned int offset, unsigned int length,
> -                                u8 *dest)
> -{
> -       return lpc_read_bytes(offset, length, dest);
> -}
> -
> -static u8 cros_ec_lpc_write_bytes(unsigned int offset, unsigned int length,
> -                                 u8 *msg)
> -{
> -       return lpc_write_bytes(offset, length, msg);
> -}
> -
> -static void cros_ec_lpc_reg_init(void)
> -{
> -}
> -
> -static void cros_ec_lpc_reg_destroy(void)
> -{
> -}
> -
> -#endif /* CONFIG_CROS_EC_LPC_MEC */
> -
>  static int ec_response_timed_out(void)
>  {
>         unsigned long one_second = jiffies + HZ;
> @@ -133,7 +128,7 @@ 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);
> @@ -153,11 +148,11 @@ 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");
> @@ -166,15 +161,15 @@ 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;
>
> @@ -187,9 +182,9 @@ 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,
> @@ -229,17 +224,17 @@ 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");
> @@ -248,14 +243,13 @@ 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,
> @@ -269,8 +263,8 @@ 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) {
> @@ -300,13 +294,13 @@ 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;
> @@ -343,10 +337,25 @@ 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 = cros_ec_lpc_mec_read_bytes;
> +       cros_ec_lpc_ops.write = cros_ec_lpc_mec_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;
> +               /* 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,
> @@ -541,13 +550,14 @@ static int __init cros_ec_lpc_init(void)
>                 return -ENODEV;
>         }
>
> -       cros_ec_lpc_reg_init();
> +       cros_ec_lpc_mec_init(EC_HOST_CMD_REGION0,
> +                            EC_LPC_ADDR_MEMMAP + EC_MEMMAP_SIZE);
>
>         /* Register the driver */
>         ret = platform_driver_register(&cros_ec_lpc_driver);
>         if (ret) {
>                 pr_err(DRV_NAME ": can't register driver: %d\n", ret);
> -               cros_ec_lpc_reg_destroy();
> +               cros_ec_lpc_mec_destroy();
>                 return ret;
>         }
>
> @@ -557,7 +567,7 @@ static int __init cros_ec_lpc_init(void)
>                 if (ret) {
>                         pr_err(DRV_NAME ": can't register device: %d\n", ret);
>                         platform_driver_unregister(&cros_ec_lpc_driver);
> -                       cros_ec_lpc_reg_destroy();
> +                       cros_ec_lpc_mec_destroy();
>                 }
>         }
>
> @@ -569,7 +579,7 @@ static void __exit cros_ec_lpc_exit(void)
>         if (!cros_ec_lpc_acpi_device_found)
>                 platform_device_unregister(&cros_ec_lpc_device);
>         platform_driver_unregister(&cros_ec_lpc_driver);
> -       cros_ec_lpc_reg_destroy();
> +       cros_ec_lpc_mec_destroy();
>  }
>
>  module_init(cros_ec_lpc_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

Reviewed-by: Nick Crews <ncrews@xxxxxxxxxxxx>

> --
> 2.20.1
>