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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 13 Jul 2018 17:34:38 +0300
Message-ID: <CAHp75VceuqTdQLXu=gQCoeSWV3zmrWdDrCe-ChxfS=24KDQSZg@mail.gmail.com>
Subject: Re: [PATCH v5] dcdbas: Add support for WSMT ACPI table
To:     Stuart Hayes <stuart.w.hayes@gmail.com>
Cc:     Mario Limonciello <Mario.Limonciello@dell.com>,
        Darren Hart <dvhart@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>
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On Tue, Jul 3, 2018 at 7:20 PM, Stuart Hayes <stuart.w.hayes@gmail.com> wrote:
>
> If the WSMT ACPI table is present and indicates that a fixed communication
> buffer should be used, use the firmware-specified buffer instead of
> allocating a buffer in memory for communications between the dcdbas driver
> and firmare.
>
> Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
> ---
> v2 Bumped driver version to 5.6.0-3.3
> v3 Removed dependency on ACPI in Kconfig
>    Moved the added #include to be in alphabetical order
>    Added comments in smi_request_store()
>    Simplified checksum code
>    Changed loop searching 0xf0000 to be more readable
>    Reworked calculation of remap_size & smi_data_buf_size
> v4 Fixed comment that starts with "Calling Interface SMI"
>    Fixed formatting of first "if" statement in dcdbas_check_wsmt()
> v5 Reworked comment that starts with "Calling Interface SMI"
>    Changed EPS scanning loop to check every 16 bytes
>

Mario, any comments on this?

For now I pushed this to my review and testing queue, thanks!

>
>  drivers/firmware/dcdbas.c | 123 +++++++++++++++++++++++++++++++++++++++++++---
>  drivers/firmware/dcdbas.h |  10 ++++
>  2 files changed, 127 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
> index 0bdea60c65dd..ae28e48ff7dc 100644
> --- a/drivers/firmware/dcdbas.c
> +++ b/drivers/firmware/dcdbas.c
> @@ -21,6 +21,7 @@
>   */
>
>  #include <linux/platform_device.h>
> +#include <linux/acpi.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/errno.h>
>  #include <linux/cpu.h>
> @@ -41,7 +42,7 @@
>  #include "dcdbas.h"
>
>  #define DRIVER_NAME            "dcdbas"
> -#define DRIVER_VERSION         "5.6.0-3.2"
> +#define DRIVER_VERSION         "5.6.0-3.3"
>  #define DRIVER_DESCRIPTION     "Dell Systems Management Base Driver"
>
>  static struct platform_device *dcdbas_pdev;
> @@ -49,19 +50,23 @@ static struct platform_device *dcdbas_pdev;
>  static u8 *smi_data_buf;
>  static dma_addr_t smi_data_buf_handle;
>  static unsigned long smi_data_buf_size;
> +static unsigned long max_smi_data_buf_size = MAX_SMI_DATA_BUF_SIZE;
>  static u32 smi_data_buf_phys_addr;
>  static DEFINE_MUTEX(smi_data_lock);
> +static u8 *eps_buffer;
>
>  static unsigned int host_control_action;
>  static unsigned int host_control_smi_type;
>  static unsigned int host_control_on_shutdown;
>
> +static bool wsmt_enabled;
> +
>  /**
>   * smi_data_buf_free: free SMI data buffer
>   */
>  static void smi_data_buf_free(void)
>  {
> -       if (!smi_data_buf)
> +       if (!smi_data_buf || wsmt_enabled)
>                 return;
>
>         dev_dbg(&dcdbas_pdev->dev, "%s: phys: %x size: %lu\n",
> @@ -86,7 +91,7 @@ static int smi_data_buf_realloc(unsigned long size)
>         if (smi_data_buf_size >= size)
>                 return 0;
>
> -       if (size > MAX_SMI_DATA_BUF_SIZE)
> +       if (size > max_smi_data_buf_size)
>                 return -EINVAL;
>
>         /* new buffer is needed */
> @@ -169,7 +174,7 @@ static ssize_t smi_data_write(struct file *filp, struct kobject *kobj,
>  {
>         ssize_t ret;
>
> -       if ((pos + count) > MAX_SMI_DATA_BUF_SIZE)
> +       if ((pos + count) > max_smi_data_buf_size)
>                 return -EINVAL;
>
>         mutex_lock(&smi_data_lock);
> @@ -322,8 +327,20 @@ static ssize_t smi_request_store(struct device *dev,
>                         ret = count;
>                 break;
>         case 1:
> -               /* Calling Interface SMI */
> -               smi_cmd->ebx = (u32) virt_to_phys(smi_cmd->command_buffer);
> +               /*
> +                * Calling Interface SMI
> +                *
> +                * Provide physical address of command buffer field within
> +                * the struct smi_cmd to BIOS.
> +                *
> +                * Because the address that smi_cmd (smi_data_buf) points to
> +                * will be from memremap() of a non-memory address if WSMT
> +                * is present, we can't use virt_to_phys() on smi_cmd, so
> +                * we have to use the physical address that was saved when
> +                * the virtual address for smi_cmd was received.
> +                */
> +               smi_cmd->ebx = smi_data_buf_phys_addr +
> +                               offsetof(struct smi_cmd, command_buffer);
>                 ret = dcdbas_smi_request(smi_cmd);
>                 if (!ret)
>                         ret = count;
> @@ -482,6 +499,93 @@ static void dcdbas_host_control(void)
>         }
>  }
>
> +/* WSMT */
> +
> +static u8 checksum(u8 *buffer, u8 length)
> +{
> +       u8 sum = 0;
> +       u8 *end = buffer + length;
> +
> +       while (buffer < end)
> +               sum += *buffer++;
> +       return sum;
> +}
> +
> +static inline struct smm_eps_table *check_eps_table(u8 *addr)
> +{
> +       struct smm_eps_table *eps = (struct smm_eps_table *)addr;
> +
> +       if (strncmp(eps->smm_comm_buff_anchor, SMM_EPS_SIG, 4) != 0)
> +               return NULL;
> +
> +       if (checksum(addr, eps->length) != 0)
> +               return NULL;
> +
> +       return eps;
> +}
> +
> +static int dcdbas_check_wsmt(void)
> +{
> +       struct acpi_table_wsmt *wsmt = NULL;
> +       struct smm_eps_table *eps = NULL;
> +       u64 remap_size;
> +       u8 *addr;
> +
> +       acpi_get_table(ACPI_SIG_WSMT, 0, (struct acpi_table_header **)&wsmt);
> +       if (!wsmt)
> +               return 0;
> +
> +       /* Check if WSMT ACPI table shows that protection is enabled */
> +       if (!(wsmt->protection_flags & ACPI_WSMT_FIXED_COMM_BUFFERS) ||
> +           !(wsmt->protection_flags & ACPI_WSMT_COMM_BUFFER_NESTED_PTR_PROTECTION))
> +               return 0;
> +
> +       /* Scan for EPS (entry point structure) */
> +       for (addr = (u8 *)__va(0xf0000);
> +            addr < (u8 *)__va(0x100000 - sizeof(struct smm_eps_table));
> +            addr += 16) {
> +               eps = check_eps_table(addr);
> +               if (eps)
> +                       break;
> +       }
> +
> +       if (!eps) {
> +               dev_dbg(&dcdbas_pdev->dev, "found WSMT, but no EPS found\n");
> +               return -ENODEV;
> +       }
> +
> +       /*
> +        * Get physical address of buffer and map to virtual address.
> +        * Table gives size in 4K pages, regardless of actual system page size.
> +        */
> +       if (upper_32_bits(eps->smm_comm_buff_addr + 8)) {
> +               dev_warn(&dcdbas_pdev->dev, "found WSMT, but EPS buffer address is above 4GB\n");
> +               return -EINVAL;
> +       }
> +       /*
> +        * Limit remap size to MAX_SMI_DATA_BUF_SIZE + 8 (since the first 8
> +        * bytes are used for a semaphore, not the data buffer itself).
> +        */
> +       remap_size = eps->num_of_4k_pages * PAGE_SIZE;
> +       if (remap_size > MAX_SMI_DATA_BUF_SIZE + 8)
> +               remap_size = MAX_SMI_DATA_BUF_SIZE + 8;
> +       eps_buffer = memremap(eps->smm_comm_buff_addr, remap_size, MEMREMAP_WB);
> +       if (!eps_buffer) {
> +               dev_warn(&dcdbas_pdev->dev, "found WSMT, but failed to map EPS buffer\n");
> +               return -ENOMEM;
> +       }
> +
> +       /* First 8 bytes is for a semaphore, not part of the smi_data_buf */
> +       smi_data_buf_phys_addr = eps->smm_comm_buff_addr + 8;
> +       smi_data_buf = eps_buffer + 8;
> +       smi_data_buf_size = remap_size - 8;
> +       max_smi_data_buf_size = smi_data_buf_size;
> +       wsmt_enabled = true;
> +       dev_info(&dcdbas_pdev->dev,
> +                "WSMT found, using firmware-provided SMI buffer.\n");
> +       return 1;
> +}
> +
>  /**
>   * dcdbas_reboot_notify: handle reboot notification for host control
>   */
> @@ -548,6 +652,11 @@ static int dcdbas_probe(struct platform_device *dev)
>
>         dcdbas_pdev = dev;
>
> +       /* Check if ACPI WSMT table specifies protected SMI buffer address */
> +       error = dcdbas_check_wsmt();
> +       if (error < 0)
> +               return error;
> +
>         /*
>          * BIOS SMI calls require buffer addresses be in 32-bit address space.
>          * This is done by setting the DMA mask below.
> @@ -635,6 +744,8 @@ static void __exit dcdbas_exit(void)
>          */
>         if (dcdbas_pdev)
>                 smi_data_buf_free();
> +       if (eps_buffer)
> +               memunmap(eps_buffer);
>         platform_device_unregister(dcdbas_pdev_reg);
>         platform_driver_unregister(&dcdbas_driver);
>  }
> diff --git a/drivers/firmware/dcdbas.h b/drivers/firmware/dcdbas.h
> index ca3cb0a54ab6..52729a494b00 100644
> --- a/drivers/firmware/dcdbas.h
> +++ b/drivers/firmware/dcdbas.h
> @@ -53,6 +53,7 @@
>  #define EXPIRED_TIMER                          (0)
>
>  #define SMI_CMD_MAGIC                          (0x534D4931)
> +#define SMM_EPS_SIG                            "$SCB"
>
>  #define DCDBAS_DEV_ATTR_RW(_name) \
>         DEVICE_ATTR(_name,0600,_name##_show,_name##_store);
> @@ -103,5 +104,14 @@ struct apm_cmd {
>
>  int dcdbas_smi_request(struct smi_cmd *smi_cmd);
>
> +struct smm_eps_table {
> +       char smm_comm_buff_anchor[4];
> +       u8 length;
> +       u8 checksum;
> +       u8 version;
> +       u64 smm_comm_buff_addr;
> +       u64 num_of_4k_pages;
> +} __packed;
> +
>  #endif /* _DCDBAS_H_ */
>
> --
> 2.14.2
>


-- 
With Best Regards,
Andy Shevchenko