linux-kernel - [PATCH] cdx: add support for driver managed dma

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Date:   Wed, 31 May 2023 17:17:59 +0530
From:   Nipun Gupta <nipun.gupta@....com>
To:     <gregkh@...uxfoundation.org>, <alex.williamson@...hat.com>,
        <linux-kernel@...r.kernel.org>
CC:     <git@....com>, <harpreet.anand@....com>,
        <pieter.jansen-van-vuuren@....com>, <nikhil.agarwal@....com>,
        <michal.simek@....com>, Nipun Gupta <nipun.gupta@....com>
Subject: [PATCH] cdx: add support for driver managed dma

The devices on cdx could be bound to drivers with the device
DMA managed by kernel drivers or user-space applications.
As multiple devices can be placed in the same IOMMU group, the
DMA on these devices must either be entirely under kernel control
or userspace control. driver_managed_dma flag should be set by
the driver which assigns the devices to be controlled by
user-space.

Signed-off-by: Nipun Gupta <nipun.gupta@....com>
Suggested-by: Alex Williamson <alex.williamson@...hat.com>
---
 drivers/cdx/cdx.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
index 38511fd36325..d2cad4c670a0 100644
--- a/drivers/cdx/cdx.c
+++ b/drivers/cdx/cdx.c
@@ -62,6 +62,8 @@
 #include <linux/mm.h>
 #include <linux/xarray.h>
 #include <linux/cdx/cdx_bus.h>
+#include <linux/iommu.h>
+#include <linux/dma-map-ops.h>
 #include "cdx.h"
 
 /* Default DMA mask for devices on a CDX bus */
@@ -257,6 +259,7 @@ static void cdx_shutdown(struct device *dev)
 
 static int cdx_dma_configure(struct device *dev)
 {
+	struct cdx_driver *cdx_drv = to_cdx_driver(dev->driver);
 	struct cdx_device *cdx_dev = to_cdx_device(dev);
 	u32 input_id = cdx_dev->req_id;
 	int ret;
@@ -267,9 +270,23 @@ static int cdx_dma_configure(struct device *dev)
 		return ret;
 	}
 
+	if (!ret && !cdx_drv->driver_managed_dma) {
+		ret = iommu_device_use_default_domain(dev);
+		if (ret)
+			arch_teardown_dma_ops(dev);
+	}
+
 	return 0;
 }
 
+static void cdx_dma_cleanup(struct device *dev)
+{
+	struct cdx_driver *cdx_drv = to_cdx_driver(dev->driver);
+
+	if (!cdx_drv->driver_managed_dma)
+		iommu_device_unuse_default_domain(dev);
+}
+
 /* show configuration fields */
 #define cdx_config_attr(field, format_string)	\
 static ssize_t	\
@@ -405,6 +422,7 @@ struct bus_type cdx_bus_type = {
 	.remove		= cdx_remove,
 	.shutdown	= cdx_shutdown,
 	.dma_configure	= cdx_dma_configure,
+	.dma_cleanup	= cdx_dma_cleanup,
 	.bus_groups	= cdx_bus_groups,
 	.dev_groups	= cdx_dev_groups,
 };
-- 
2.17.1