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Subject[PATCH v5] dcdbas: Add support for WSMT ACPI table
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Date

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


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
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