VMCI: dma dg: add support for DMA datagrams sends

Use DMA based send operation from the transmit buffer instead of the
iowrite8_rep based datagram send when DMA datagrams are supported.

The outgoing datagram is sent as inline data in the VMCI transmit
buffer. Once the header has been configured, the send is initiated
by writing the lower 32 bit of the buffer base address to the
VMCI_DATA_OUT_LOW_ADDR register. Only then will the device process
the header and the datagram itself. Following that, the driver busy
waits (it isn't possible to sleep on the send path) for the header
busy flag to change - indicating that the send is complete.

Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Signed-off-by: Jorgen Hansen <jhansen@vmware.com>
Link: https://lore.kernel.org/r/20220207102725.2742-8-jhansen@vmware.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 43 insertions, 2 deletions

diff --git a/drivers/misc/vmw_vmci/vmci_guest.c b/drivers/misc/vmw_vmci/vmci_guest.c
index 36eade15ba87..bf524217914e 100644
--- a/drivers/misc/vmw_vmci/vmci_guest.c
+++ b/drivers/misc/vmw_vmci/vmci_guest.c
@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/processor.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/init.h>
@@ -114,6 +115,47 @@ static void vmci_write_reg(struct vmci_guest_device *dev, u32 val, u32 reg)
 		iowrite32(val, dev->iobase + reg);
 }
 
+static int vmci_write_data(struct vmci_guest_device *dev,
+			   struct vmci_datagram *dg)
+{
+	int result;
+
+	if (dev->mmio_base != NULL) {
+		struct vmci_data_in_out_header *buffer_header = dev->tx_buffer;
+		u8 *dg_out_buffer = (u8 *)(buffer_header + 1);
+
+		if (VMCI_DG_SIZE(dg) > VMCI_MAX_DG_SIZE)
+			return VMCI_ERROR_INVALID_ARGS;
+
+		/*
+		 * Initialize send buffer with outgoing datagram
+		 * and set up header for inline data. Device will
+		 * not access buffer asynchronously - only after
+		 * the write to VMCI_DATA_OUT_LOW_ADDR.
+		 */
+		memcpy(dg_out_buffer, dg, VMCI_DG_SIZE(dg));
+		buffer_header->opcode = 0;
+		buffer_header->size = VMCI_DG_SIZE(dg);
+		buffer_header->busy = 1;
+
+		vmci_write_reg(dev, lower_32_bits(dev->tx_buffer_base),
+			       VMCI_DATA_OUT_LOW_ADDR);
+
+		/* Caller holds a spinlock, so cannot block. */
+		spin_until_cond(buffer_header->busy == 0);
+
+		result = vmci_read_reg(vmci_dev_g, VMCI_RESULT_LOW_ADDR);
+		if (result == VMCI_SUCCESS)
+			result = (int)buffer_header->result;
+	} else {
+		iowrite8_rep(dev->iobase + VMCI_DATA_OUT_ADDR,
+			     dg, VMCI_DG_SIZE(dg));
+		result = vmci_read_reg(vmci_dev_g, VMCI_RESULT_LOW_ADDR);
+	}
+
+	return result;
+}
+
 /*
  * VM to hypervisor call mechanism. We use the standard VMware naming
  * convention since shared code is calling this function as well.
@@ -139,8 +181,7 @@ int vmci_send_datagram(struct vmci_datagram *dg)
 	spin_lock_irqsave(&vmci_dev_spinlock, flags);
 
 	if (vmci_dev_g) {
-		iowrite8_rep(vmci_dev_g->iobase + VMCI_DATA_OUT_ADDR,
-			     dg, VMCI_DG_SIZE(dg));
+		vmci_write_data(vmci_dev_g, dg);
 		result = vmci_read_reg(vmci_dev_g, VMCI_RESULT_LOW_ADDR);
 	} else {
 		result = VMCI_ERROR_UNAVAILABLE;