linux-kernel - [PATCH] uio_hv_generic: Enable interrupt for low speed VMBus devices

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Message-Id: <1665685754-13971-1-git-send-email-ssengar@linux.microsoft.com>
Date:   Thu, 13 Oct 2022 11:29:14 -0700
From:   Saurabh Sengar <ssengar@...ux.microsoft.com>
To:     ssengar@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        longli@...rosoft.com, gregkh@...uxfoundation.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        mikelley@...rosoft.com
Subject: [PATCH] uio_hv_generic: Enable interrupt for low speed VMBus devices

Hyper-V is adding some "specialty" synthetic devices. Instead of writing
new kernel-level VMBus drivers for these devices, the devices will be
presented to user space via this existing Hyper-V generic UIO driver, so
that a user space driver can handle the device. Since these new synthetic
devices are low speed devices, they don't support monitor bits and we must
use vmbus_setevent() to enable interrupts from the host.

Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
---
 drivers/uio/uio_hv_generic.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
index c08a6cfd119f..8e5aa4a1247f 100644
--- a/drivers/uio/uio_hv_generic.c
+++ b/drivers/uio/uio_hv_generic.c
@@ -84,6 +84,9 @@ hv_uio_irqcontrol(struct uio_info *info, s32 irq_state)
 	dev->channel->inbound.ring_buffer->interrupt_mask = !irq_state;
 	virt_mb();
 
+	if (!dev->channel->offermsg.monitor_allocated && irq_state)
+		vmbus_setevent(dev->channel);
+
 	return 0;
 }
 
@@ -239,12 +242,6 @@ hv_uio_probe(struct hv_device *dev,
 	void *ring_buffer;
 	int ret;
 
-	/* Communicating with host has to be via shared memory not hypercall */
-	if (!channel->offermsg.monitor_allocated) {
-		dev_err(&dev->device, "vmbus channel requires hypercall\n");
-		return -ENOTSUPP;
-	}
-
 	pdata = devm_kzalloc(&dev->device, sizeof(*pdata), GFP_KERNEL);
 	if (!pdata)
 		return -ENOMEM;
-- 
2.34.1