cxl/memdev: Make mailbox functionality optional

In support of the Linux CXL core scaling for a wider set of CXL devices,
allow for the creation of memdevs with some memory device capabilities
disabled. Specifically, allow for CXL devices outside of those claiming
to be compliant with the generic CXL memory device class code, like
vendor specific Type-2/3 devices that host CXL.mem. This implies, allow
for the creation of memdevs that only support component-registers, not
necessarily memory-device-registers (like mailbox registers). A memdev
derived from a CXL endpoint that does not support generic class code
expectations is tagged "CXL_DEVTYPE_DEVMEM", while a memdev derived from a
class-code compliant endpoint is tagged "CXL_DEVTYPE_CLASSMEM".

The primary assumption of a CXL_DEVTYPE_DEVMEM memdev is that it
optionally may not host a mailbox. Disable the command passthrough ioctl
for memdevs that are not CXL_DEVTYPE_CLASSMEM, and return empty strings
from memdev attributes associated with data retrieved via the
class-device-standard IDENTIFY command. Note that empty strings were
chosen over attribute visibility to maintain compatibility with shipping
versions of cxl-cli that expect those attributes to always be present.
Once cxl-cli has dropped that requirement this workaround can be
deprecated.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/168679260782.3436160.7587293613945445365.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 10 insertions, 1 deletions

diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index ab9d455e8579..1990a5940b7c 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -1272,6 +1272,7 @@ struct cxl_memdev_state *cxl_memdev_state_create(struct device *dev)
 	mutex_init(&mds->mbox_mutex);
 	mutex_init(&mds->event.log_lock);
 	mds->cxlds.dev = dev;
+	mds->cxlds.type = CXL_DEVTYPE_CLASSMEM;
 
 	return mds;
 }
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index 15434b1b4909..3f2d54f30548 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -41,6 +41,8 @@ static ssize_t firmware_version_show(struct device *dev,
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
 
+	if (!mds)
+		return sysfs_emit(buf, "\n");
 	return sysfs_emit(buf, "%.16s\n", mds->firmware_version);
 }
 static DEVICE_ATTR_RO(firmware_version);
@@ -52,6 +54,8 @@ static ssize_t payload_max_show(struct device *dev,
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
 
+	if (!mds)
+		return sysfs_emit(buf, "\n");
 	return sysfs_emit(buf, "%zu\n", mds->payload_size);
 }
 static DEVICE_ATTR_RO(payload_max);
@@ -63,6 +67,8 @@ static ssize_t label_storage_size_show(struct device *dev,
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
 
+	if (!mds)
+		return sysfs_emit(buf, "\n");
 	return sysfs_emit(buf, "%zu\n", mds->lsa_size);
 }
 static DEVICE_ATTR_RO(label_storage_size);
@@ -517,10 +523,12 @@ static long cxl_memdev_ioctl(struct file *file, unsigned int cmd,
 			     unsigned long arg)
 {
 	struct cxl_memdev *cxlmd = file->private_data;
+	struct cxl_dev_state *cxlds;
 	int rc = -ENXIO;
 
 	down_read(&cxl_memdev_rwsem);
-	if (cxlmd->cxlds)
+	cxlds = cxlmd->cxlds;
+	if (cxlds && cxlds->type == CXL_DEVTYPE_CLASSMEM)
 		rc = __cxl_memdev_ioctl(cxlmd, cmd, arg);
 	up_read(&cxl_memdev_rwsem);