netdev - [PATCH v2] vhost-vdpa: print warning when vhost_vdpa_alloc

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Date:   Thu,  2 Feb 2023 10:42:12 +0200
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     mst@...hat.com, jasowang@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, Alvaro Karsz <alvaro.karsz@...id-run.com>,
        Eugenio Perez Martin <eperezma@...hat.com>
Subject: [PATCH v2] vhost-vdpa: print warning when vhost_vdpa_alloc_domain fails

Add a print explaining why vhost_vdpa_alloc_domain failed if the device
is not IOMMU cache coherent capable.

Without this print, we have no hint why the operation failed.

For example:

$ virsh start <domain>
	error: Failed to start domain <domain>
	error: Unable to open '/dev/vhost-vdpa-<idx>' for vdpa device:
	       Unknown error 524

Suggested-by: Eugenio Perez Martin <eperezma@...hat.com>
Signed-off-by: Alvaro Karsz <alvaro.karsz@...id-run.com>

---
v2:
	- replace dev_err with dev_warn_once.

 drivers/vhost/vdpa.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 23db92388393..135f8aa70fb2 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1151,8 +1151,11 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
 	if (!bus)
 		return -EFAULT;
 
-	if (!device_iommu_capable(dma_dev, IOMMU_CAP_CACHE_COHERENCY))
+	if (!device_iommu_capable(dma_dev, IOMMU_CAP_CACHE_COHERENCY)) {
+		dev_warn_once(&v->dev,
+			      "Failed to allocate domain, device is not IOMMU cache coherent capable\n");
 		return -ENOTSUPP;
+	}
 
 	v->domain = iommu_domain_alloc(bus);
 	if (!v->domain)
-- 
2.34.1