[PATCH 04/14] cxl/mem: Implement polled mode mailbox

Ben Widawsky
2021-01-30T00:28:25Z

Provide enough functionality to utilize the mailbox of a memory device.
The mailbox is used to interact with the firmware running on the memory
device.

The CXL specification defines separate capabilities for the mailbox and
the memory device. The mailbox interface has a doorbell to indicate
ready to accept commands and the memory device has a capability register
that indicates the mailbox interface is ready. The expectation is that
the doorbell-ready is always later than the memory-device-indication
that the mailbox is ready.

Create a function to handle sending a command, optionally with a
payload, to the memory device, polling on a result, and then optionally
copying out the payload. The algorithm for doing this comes straight out
of the CXL 2.0 specification.

Primary mailboxes are capable of generating an interrupt when submitting
a command in the background. That implementation is saved for a later
time.

Secondary mailboxes aren't implemented at this time.

The flow is proven with one implemented command, "identify". Because the
class code has already told the driver this is a memory device and the
identify command is mandatory.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
drivers/cxl/Kconfig | 14 ++
drivers/cxl/cxl.h | 39 +++++
drivers/cxl/mem.c | 342 +++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 394 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 3b66b46af8a0..fe591f74af96 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -32,4 +32,18 @@ config CXL_MEM
Chapter 2.3 Type 3 CXL Device in the CXL 2.0 specification.

If unsure say 'm'.
+
+config CXL_MEM_INSECURE_DEBUG
+ bool "CXL.mem debugging"
+ depends on CXL_MEM
+ help
+ Enable debug of all CXL command payloads.
+
+ Some CXL devices and controllers support encryption and other
+ security features. The payloads for the commands that enable
+ those features may contain sensitive clear-text security
+ material. Disable debug of those command payloads by default.
+ If you are a kernel developer actively working on CXL
+ security enabling say Y, otherwise say N.
+
endif
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index a3da7f8050c4..df3d97154b63 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -31,9 +31,36 @@
#define CXLDEV_MB_CAPS_OFFSET 0x00
#define CXLDEV_MB_CAP_PAYLOAD_SIZE_MASK GENMASK(4, 0)
#define CXLDEV_MB_CTRL_OFFSET 0x04
+#define CXLDEV_MB_CTRL_DOORBELL BIT(0)
#define CXLDEV_MB_CMD_OFFSET 0x08
+#define CXLDEV_MB_CMD_COMMAND_OPCODE_MASK GENMASK(15, 0)
+#define CXLDEV_MB_CMD_PAYLOAD_LENGTH_MASK GENMASK(36, 16)
#define CXLDEV_MB_STATUS_OFFSET 0x10
+#define CXLDEV_MB_STATUS_RET_CODE_MASK GENMASK(47, 32)
#define CXLDEV_MB_BG_CMD_STATUS_OFFSET 0x18
+#define CXLDEV_MB_PAYLOAD_OFFSET 0x20
+
+/* Memory Device (CXL 2.0 - 8.2.8.5.1.1) */
+#define CXLMDEV_STATUS_OFFSET 0x0
+#define CXLMDEV_DEV_FATAL BIT(0)
+#define CXLMDEV_FW_HALT BIT(1)
+#define CXLMDEV_STATUS_MEDIA_STATUS_MASK GENMASK(3, 2)
+#define CXLMDEV_MS_NOT_READY 0
+#define CXLMDEV_MS_READY 1
+#define CXLMDEV_MS_ERROR 2
+#define CXLMDEV_MS_DISABLED 3
+#define CXLMDEV_READY(status) \
+ (CXL_GET_FIELD(status, CXLMDEV_STATUS_MEDIA_STATUS) == CXLMDEV_MS_READY)
+#define CXLMDEV_MBOX_IF_READY BIT(4)
+#define CXLMDEV_RESET_NEEDED_SHIFT 5
+#define CXLMDEV_RESET_NEEDED_MASK GENMASK(7, 5)
+#define CXLMDEV_RESET_NEEDED_NOT 0
+#define CXLMDEV_RESET_NEEDED_COLD 1
+#define CXLMDEV_RESET_NEEDED_WARM 2
+#define CXLMDEV_RESET_NEEDED_HOT 3
+#define CXLMDEV_RESET_NEEDED_CXL 4
+#define CXLMDEV_RESET_NEEDED(status) \
+ (CXL_GET_FIELD(status, CXLMDEV_RESET_NEEDED) != CXLMDEV_RESET_NEEDED_NOT)

/**
* struct cxl_mem - A CXL memory device
@@ -44,6 +71,16 @@ struct cxl_mem {
struct pci_dev *pdev;
void __iomem *regs;

+ struct {
+ struct range range;
+ } pmem;
+
+ struct {
+ struct range range;
+ } ram;
+
+ char firmware_version[0x10];
+
/* Cap 0001h - CXL_CAP_CAP_ID_DEVICE_STATUS */
struct {
void __iomem *regs;
@@ -51,6 +88,7 @@ struct cxl_mem {

/* Cap 0002h - CXL_CAP_CAP_ID_PRIMARY_MAILBOX */
struct {
+ struct mutex mutex; /* Protects device mailbox and firmware */
void __iomem *regs;
size_t payload_size;
} mbox;
@@ -89,5 +127,6 @@ struct cxl_mem {

cxl_reg(status);
cxl_reg(mbox);
+cxl_reg(mem);

#endif /* __CXL_H__ */
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index fa14d51243ee..69ed15bfa5d4 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -6,6 +6,270 @@
#include "pci.h"
#include "cxl.h"

+#define cxl_doorbell_busy(cxlm) \
+ (cxl_read_mbox_reg32(cxlm, CXLDEV_MB_CTRL_OFFSET) & \
+ CXLDEV_MB_CTRL_DOORBELL)
+
+#define CXL_MAILBOX_TIMEOUT_US 2000
+
+enum opcode {
+ CXL_MBOX_OP_IDENTIFY = 0x4000,
+ CXL_MBOX_OP_MAX = 0x10000
+};
+
+/**
+ * struct mbox_cmd - A command to be submitted to hardware.
+ * @opcode: (input) The command set and command submitted to hardware.
+ * @payload_in: (input) Pointer to the input payload.
+ * @payload_out: (output) Pointer to the output payload. Must be allocated by
+ * the caller.
+ * @size_in: (input) Number of bytes to load from @payload.
+ * @size_out: (output) Number of bytes loaded into @payload.
+ * @return_code: (output) Error code returned from hardware.
+ *
+ * This is the primary mechanism used to send commands to the hardware.
+ * All the fields except @payload_* correspond exactly to the fields described in
+ * Command Register section of the CXL 2.0 spec (8.2.8.4.5). @payload_in and
+ * @payload_out are written to, and read from the Command Payload Registers
+ * defined in (8.2.8.4.8).
+ */
+struct mbox_cmd {
+ u16 opcode;
+ void *payload_in;
+ void *payload_out;
+ size_t size_in;
+ size_t size_out;
+ u16 return_code;
+#define CXL_MBOX_SUCCESS 0
+};
+
+static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
+{
+ const int timeout = msecs_to_jiffies(CXL_MAILBOX_TIMEOUT_US);
+ const unsigned long start = jiffies;
+ unsigned long end = start;
+
+ while (cxl_doorbell_busy(cxlm)) {
+ end = jiffies;
+
+ if (time_after(end, start + timeout)) {
+ /* Check again in case preempted before timeout test */
+ if (!cxl_doorbell_busy(cxlm))
+ break;
+ return -ETIMEDOUT;
+ }
+ cpu_relax();
+ }
+
+ dev_dbg(&cxlm->pdev->dev, "Doorbell wait took %dms",
+ jiffies_to_msecs(end) - jiffies_to_msecs(start));
+ return 0;
+}
+
+static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
+ struct mbox_cmd *mbox_cmd)
+{
+ dev_warn(&cxlm->pdev->dev, "Mailbox command timed out\n");
+ dev_info(&cxlm->pdev->dev,
+ "\topcode: 0x%04x\n"
+ "\tpayload size: %zub\n",
+ mbox_cmd->opcode, mbox_cmd->size_in);
+
+ if (IS_ENABLED(CONFIG_CXL_MEM_INSECURE_DEBUG)) {
+ print_hex_dump_debug("Payload ", DUMP_PREFIX_OFFSET, 16, 1,
+ mbox_cmd->payload_in, mbox_cmd->size_in,
+ true);
+ }
+
+ /* Here's a good place to figure out if a device reset is needed */
+}
+
+/**
+ * cxl_mem_mbox_send_cmd() - Send a mailbox command to a memory device.
+ * @cxlm: The CXL memory device to communicate with.
+ * @mbox_cmd: Command to send to the memory device.
+ *
+ * Context: Any context. Expects mbox_lock to be held.
+ * Return: -ETIMEDOUT if timeout occurred waiting for completion. 0 on success.
+ * Caller should check the return code in @mbox_cmd to make sure it
+ * succeeded.
+ *
+ * This is a generic form of the CXL mailbox send command, thus the only I/O
+ * operations used are cxl_read_mbox_reg(). Memory devices, and perhaps other
+ * types of CXL devices may have further information available upon error
+ * conditions.
+ *
+ * The CXL spec allows for up to two mailboxes. The intention is for the primary
+ * mailbox to be OS controlled and the secondary mailbox to be used by system
+ * firmware. This allows the OS and firmware to communicate with the device and
+ * not need to coordinate with each other. The driver only uses the primary
+ * mailbox.
+ */
+static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm,
+ struct mbox_cmd *mbox_cmd)
+{
+ void __iomem *payload = cxlm->mbox.regs + CXLDEV_MB_PAYLOAD_OFFSET;
+ u64 cmd_reg, status_reg;
+ size_t out_len;
+ int rc;
+
+ lockdep_assert_held(&cxlm->mbox.mutex);
+
+ /*
+ * Here are the steps from 8.2.8.4 of the CXL 2.0 spec.
+ * 1. Caller reads MB Control Register to verify doorbell is clear
+ * 2. Caller writes Command Register
+ * 3. Caller writes Command Payload Registers if input payload is non-empty
+ * 4. Caller writes MB Control Register to set doorbell
+ * 5. Caller either polls for doorbell to be clear or waits for interrupt if configured
+ * 6. Caller reads MB Status Register to fetch Return code
+ * 7. If command successful, Caller reads Command Register to get Payload Length
+ * 8. If output payload is non-empty, host reads Command Payload Registers
+ *
+ * Hardware is free to do whatever it wants before the doorbell is
+ * rung, and isn't allowed to change anything after it clears the
+ * doorbell. As such, steps 2 and 3 can happen in any order, and steps
+ * 6, 7, 8 can also happen in any order (though some orders might not
+ * make sense).
+ */
+
+ /* #1 */
+ if (cxl_doorbell_busy(cxlm)) {
+ dev_err_ratelimited(&cxlm->pdev->dev,
+ "Mailbox re-busy after acquiring\n");
+ return -EBUSY;
+ }
+
+ cmd_reg = CXL_SET_FIELD(mbox_cmd->opcode, CXLDEV_MB_CMD_COMMAND_OPCODE);
+ if (mbox_cmd->size_in) {
+ if (WARN_ON(!mbox_cmd->payload_in))
+ return -EINVAL;
+
+ cmd_reg |= CXL_SET_FIELD(mbox_cmd->size_in,
+ CXLDEV_MB_CMD_PAYLOAD_LENGTH);
+ memcpy_toio(payload, mbox_cmd->payload_in, mbox_cmd->size_in);
+ }
+
+ /* #2, #3 */
+ cxl_write_mbox_reg64(cxlm, CXLDEV_MB_CMD_OFFSET, cmd_reg);
+
+ /* #4 */
+ dev_dbg(&cxlm->pdev->dev, "Sending command\n");
+ cxl_write_mbox_reg32(cxlm, CXLDEV_MB_CTRL_OFFSET,
+ CXLDEV_MB_CTRL_DOORBELL);
+
+ /* #5 */
+ rc = cxl_mem_wait_for_doorbell(cxlm);
+ if (rc == -ETIMEDOUT) {
+ cxl_mem_mbox_timeout(cxlm, mbox_cmd);
+ return rc;
+ }
+
+ /* #6 */
+ status_reg = cxl_read_mbox_reg64(cxlm, CXLDEV_MB_STATUS_OFFSET);
+ mbox_cmd->return_code =
+ CXL_GET_FIELD(status_reg, CXLDEV_MB_STATUS_RET_CODE);
+
+ if (mbox_cmd->return_code != 0) {
+ dev_dbg(&cxlm->pdev->dev, "Mailbox operation had an error\n");
+ return 0;
+ }
+
+ /* #7 */
+ cmd_reg = cxl_read_mbox_reg64(cxlm, CXLDEV_MB_CMD_OFFSET);
+ out_len = CXL_GET_FIELD(cmd_reg, CXLDEV_MB_CMD_PAYLOAD_LENGTH);
+
+ /* #8 */
+ if (out_len && mbox_cmd->payload_out)
+ memcpy_fromio(mbox_cmd->payload_out, payload, out_len);
+
+ mbox_cmd->size_out = out_len;
+
+ return 0;
+}
+
+/**
+ * cxl_mem_mbox_get() - Acquire exclusive access to the mailbox.
+ * @cxlm: The memory device to gain access to.
+ *
+ * Context: Any context. Takes the mbox_lock.
+ * Return: 0 if exclusive access was acquired.
+ */
+static int cxl_mem_mbox_get(struct cxl_mem *cxlm)
+{
+ struct device *dev = &cxlm->pdev->dev;
+ int rc = -EBUSY;
+ u64 md_status;
+
+ mutex_lock_io(&cxlm->mbox.mutex);
+
+ /*
+ * XXX: There is some amount of ambiguity in the 2.0 version of the spec
+ * around the mailbox interface ready (8.2.8.5.1.1). The purpose of the
+ * bit is to allow firmware running on the device to notify the driver
+ * that it's ready to receive commands. It is unclear if the bit needs
+ * to be read for each transaction mailbox, ie. the firmware can switch
+ * it on and off as needed. Second, there is no defined timeout for
+ * mailbox ready, like there is for the doorbell interface.
+ *
+ * Assumptions:
+ * 1. The firmware might toggle the Mailbox Interface Ready bit, check
+ * it for every command.
+ *
+ * 2. If the doorbell is clear, the firmware should have first set the
+ * Mailbox Interface Ready bit. Therefore, waiting for the doorbell
+ * to be ready is sufficient.
+ */
+ rc = cxl_mem_wait_for_doorbell(cxlm);
+ if (rc) {
+ dev_warn(dev, "Mailbox interface not ready\n");
+ goto out;
+ }
+
+ md_status = cxl_read_mem_reg64(cxlm, CXLMDEV_STATUS_OFFSET);
+ if (!(md_status & CXLMDEV_MBOX_IF_READY && CXLMDEV_READY(md_status))) {
+ dev_err(dev,
+ "mbox: reported doorbell ready, but not mbox ready\n");
+ goto out;
+ }
+
+ /*
+ * Hardware shouldn't allow a ready status but also have failure bits
+ * set. Spit out an error, this should be a bug report
+ */
+ rc = -EFAULT;
+ if (md_status & CXLMDEV_DEV_FATAL) {
+ dev_err(dev, "mbox: reported ready, but fatal\n");
+ goto out;
+ }
+ if (md_status & CXLMDEV_FW_HALT) {
+ dev_err(dev, "mbox: reported ready, but halted\n");
+ goto out;
+ }
+ if (CXLMDEV_RESET_NEEDED(md_status)) {
+ dev_err(dev, "mbox: reported ready, but reset needed\n");
+ goto out;
+ }
+
+ /* with lock held */
+ return 0;
+
+out:
+ mutex_unlock(&cxlm->mbox.mutex);
+ return rc;
+}
+
+/**
+ * cxl_mem_mbox_put() - Release exclusive access to the mailbox.
+ * @cxlm: The CXL memory device to communicate with.
+ *
+ * Context: Any context. Expects mbox_lock to be held.
+ */
+static void cxl_mem_mbox_put(struct cxl_mem *cxlm)
+{
+ mutex_unlock(&cxlm->mbox.mutex);
+}
+
/**
* cxl_mem_setup_regs() - Setup necessary MMIO.
* @cxlm: The CXL memory device to communicate with.
@@ -142,6 +406,8 @@ static struct cxl_mem *cxl_mem_create(struct pci_dev *pdev, u32 reg_lo,
return NULL;
}

+ mutex_init(&cxlm->mbox.mutex);
+
regs = pcim_iomap_table(pdev)[bar];
cxlm->pdev = pdev;
cxlm->regs = regs + offset;
@@ -174,6 +440,76 @@ static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
return 0;
}

+/**
+ * cxl_mem_identify() - Send the IDENTIFY command to the device.
+ * @cxlm: The device to identify.
+ *
+ * Return: 0 if identify was executed successfully.
+ *
+ * This will dispatch the identify command to the device and on success populate
+ * structures to be exported to sysfs.
+ */
+static int cxl_mem_identify(struct cxl_mem *cxlm)
+{
+ struct cxl_mbox_identify {
+ char fw_revision[0x10];
+ __le64 total_capacity;
+ __le64 volatile_capacity;
+ __le64 persistent_capacity;
+ __le64 partition_align;
+ __le16 info_event_log_size;
+ __le16 warning_event_log_size;
+ __le16 failure_event_log_size;
+ __le16 fatal_event_log_size;
+ __le32 lsa_size;
+ u8 poison_list_max_mer[3];
+ __le16 inject_poison_limit;
+ u8 poison_caps;
+ u8 qos_telemetry_caps;
+ } __packed id;
+ struct mbox_cmd mbox_cmd;
+ int rc;
+
+ /* Retrieve initial device memory map */
+ rc = cxl_mem_mbox_get(cxlm);
+ if (rc)
+ return rc;
+
+ mbox_cmd = (struct mbox_cmd){
+ .opcode = CXL_MBOX_OP_IDENTIFY,
+ .payload_out = &id,
+ .size_in = 0,
+ };
+ rc = cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
+ cxl_mem_mbox_put(cxlm);
+ if (rc)
+ return rc;
+
+ /* TODO: Handle retry or reset responses from firmware. */
+ if (mbox_cmd.return_code != CXL_MBOX_SUCCESS) {
+ dev_err(&cxlm->pdev->dev, "Mailbox command failed (%d)\n",
+ mbox_cmd.return_code);
+ return -ENXIO;
+ }
+
+ if (mbox_cmd.size_out != sizeof(id))
+ return -ENXIO;
+
+ /*
+ * TODO: enumerate DPA map, as 'ram' and 'pmem' do not alias.
+ * For now, only the capacity is exported in sysfs
+ */
+ cxlm->ram.range.start = 0;
+ cxlm->ram.range.end = le64_to_cpu(id.volatile_capacity) - 1;
+
+ cxlm->pmem.range.start = 0;
+ cxlm->pmem.range.end = le64_to_cpu(id.persistent_capacity) - 1;
+
+ memcpy(cxlm->firmware_version, id.fw_revision, sizeof(id.fw_revision));
+
+ return rc;
+}
+
static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
{
struct device *dev = &pdev->dev;
@@ -219,7 +555,11 @@ static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
if (rc)
return rc;

- return cxl_mem_setup_mailbox(cxlm);
+ rc = cxl_mem_setup_mailbox(cxlm);
+ if (rc)
+ return rc;
+
+ return cxl_mem_identify(cxlm);
}

static const struct pci_device_id cxl_mem_pci_tbl[] = {
--
2.30.0