cxl/pci: Implement Interface Ready Timeout

The original driver implementation used the doorbell timeout for the
Mailbox Interface Ready bit to piggy back off of, since the latter does
not have a defined timeout. This functionality, introduced in commit
8adaf747c9f0 ("cxl/mem: Find device capabilities"), needs improvement as
the recent "Add Mailbox Ready Time" ECN timeout indicates that the
mailbox ready time can be significantly longer that 2 seconds.

While the specification limits the maximum timeout to 256s, the cxl_pci
driver gives up on the mailbox after 60s. This value corresponds with
important timeout values already present in the kernel. A module
parameter is provided as an emergency override and represents the
default Linux policy for all devices.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
[djbw: add modparam, drop check_device_status()]
Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/164367306565.208548.1932299464604450843.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index 8dc91fd3396a398f1dc102a0f1cc27e4ac2424fb..cc0cdd7e9de3ccb4c2719dcf6a4e84821cc691f9 100644 (file)
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
 #include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/moduleparam.h>
 #include <linux/module.h>
+#include <linux/delay.h>
 #include <linux/sizes.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
@@ -35,6 +37,20 @@
 /* CXL 2.0 - 8.2.8.4 */
 #define CXL_MAILBOX_TIMEOUT_MS (2 * HZ)
 
+/*
+ * CXL 2.0 ECN "Add Mailbox Ready Time" defines a capability field to
+ * dictate how long to wait for the mailbox to become ready. The new
+ * field allows the device to tell software the amount of time to wait
+ * before mailbox ready. This field per the spec theoretically allows
+ * for up to 255 seconds. 255 seconds is unreasonably long, its longer
+ * than the maximum SATA port link recovery wait. Default to 60 seconds
+ * until someone builds a CXL device that needs more time in practice.
+ */
+static unsigned short mbox_ready_timeout = 60;
+module_param(mbox_ready_timeout, ushort, 0644);
+MODULE_PARM_DESC(mbox_ready_timeout,
+                "seconds to wait for mailbox ready status");
+
 static int cxl_pci_mbox_wait_for_doorbell(struct cxl_dev_state *cxlds)
 {
        const unsigned long start = jiffies;
@@ -281,6 +297,25 @@ static int cxl_pci_mbox_send(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *c
 static int cxl_pci_setup_mailbox(struct cxl_dev_state *cxlds)
 {
        const int cap = readl(cxlds->regs.mbox + CXLDEV_MBOX_CAPS_OFFSET);
+       unsigned long timeout;
+       u64 md_status;
+
+       timeout = jiffies + mbox_ready_timeout * HZ;
+       do {
+               md_status = readq(cxlds->regs.memdev + CXLMDEV_STATUS_OFFSET);
+               if (md_status & CXLMDEV_MBOX_IF_READY)
+                       break;
+               if (msleep_interruptible(100))
+                       break;
+       } while (!time_after(jiffies, timeout));
+
+       if (!(md_status & CXLMDEV_MBOX_IF_READY)) {
+               dev_err(cxlds->dev,
+                       "timeout awaiting mailbox ready, device state:%s%s\n",
+                       md_status & CXLMDEV_DEV_FATAL ? " fatal" : "",
+                       md_status & CXLMDEV_FW_HALT ? " firmware-halt" : "");
+               return -EIO;
+       }
 
        cxlds->mbox_send = cxl_pci_mbox_send;
        cxlds->payload_size =