[PATCH v2] dmaengine: idxd: add module parameter to force disable of SVA

[Dave Jiang <dave.jiang@xxxxxxxxx>]

Add a module parameter that overrides the SVA feature enabling. This keeps
the driver in legacy mode even when intel_iommu=sm_on is set. In this mode,
the descriptor fields must be programmed with dma_addr_t from the Linux DMA
API for source, destination, and completion descriptors.

Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
---

v2: 
- Add documentation (Vinod)

 Documentation/admin-guide/kernel-parameters.txt |    6 ++++++
 drivers/dma/idxd/init.c                         |    8 +++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c722ec19cd00..c25786b95419 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1673,6 +1673,12 @@
 			In such case C2/C3 won't be used again.
 			idle=nomwait: Disable mwait for CPU C-states
 
+	idxd.sva=	[HW]
+			Format: <bool>
+			Allow force disabling of Shared Virtual Memory (SVA)
+			support for the idxd driver. By default it is set to
+			true (1).
+
 	ieee754=	[MIPS] Select IEEE Std 754 conformance mode
 			Format: { strict | legacy | 2008 | relaxed }
 			Default: strict
diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
index 25cc947c6179..9687a24ff982 100644
--- a/drivers/dma/idxd/init.c
+++ b/drivers/dma/idxd/init.c
@@ -26,6 +26,10 @@ MODULE_VERSION(IDXD_DRIVER_VERSION);
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Intel Corporation");
 
+static bool sva = true;
+module_param(sva, bool, 0644);
+MODULE_PARM_DESC(sva, "Toggle SVA support on/off");
+
 #define DRV_NAME "idxd"
 
 bool support_enqcmd;
@@ -338,12 +342,14 @@ static int idxd_probe(struct idxd_device *idxd)
 	idxd_device_init_reset(idxd);
 	dev_dbg(dev, "IDXD reset complete\n");
 
-	if (IS_ENABLED(CONFIG_INTEL_IDXD_SVM)) {
+	if (IS_ENABLED(CONFIG_INTEL_IDXD_SVM) && sva) {
 		rc = idxd_enable_system_pasid(idxd);
 		if (rc < 0)
 			dev_warn(dev, "Failed to enable PASID. No SVA support: %d\n", rc);
 		else
 			set_bit(IDXD_FLAG_PASID_ENABLED, &idxd->flags);
+	} else if (!sva) {
+		dev_warn(dev, "User forced SVA off via module param.\n");
 	}
 
 	idxd_read_caps(idxd);