linux-kernel - [PATCH] virtio: Simplify DMA setting

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Message-Id: <fc97319a44d41d8b7eb127e1facdef4139ed77ac.1641625657.git.christophe.jaillet@wanadoo.fr>
Date:   Sat,  8 Jan 2022 08:08:43 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     mst@...hat.com, jasowang@...hat.com
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] virtio: Simplify DMA setting

As stated in [1], dma_set_mask() with a 64-bit mask will never fail if
dev->dma_mask is non-NULL.
So, if it fails, the 32 bits case will also fail for the same reason.

Simplify code and remove some dead code accordingly.


While at it, include directly <linux/dma-mapping.h> instead on relying on
indirect inclusion.

[1]: https://lkml.org/lkml/2021/6/7/398

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 drivers/virtio/virtio_mmio.c           | 4 +---
 drivers/virtio/virtio_pci_legacy_dev.c | 7 +++----
 drivers/virtio/virtio_pci_modern_dev.c | 6 ++----
 3 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 56128b9c46eb..aa1efa854de1 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -617,9 +617,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
 	}
 	if (rc)
-		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
-	if (rc)
-		dev_warn(&pdev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
+		dev_warn(&pdev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
 
 	platform_set_drvdata(pdev, vm_dev);
 
diff --git a/drivers/virtio/virtio_pci_legacy_dev.c b/drivers/virtio/virtio_pci_legacy_dev.c
index 677d1f68bc9b..52b1c4dd43fe 100644
--- a/drivers/virtio/virtio_pci_legacy_dev.c
+++ b/drivers/virtio/virtio_pci_legacy_dev.c
@@ -2,6 +2,7 @@
 
 #include "linux/virtio_pci.h"
 #include <linux/virtio_pci_legacy.h>
+#include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 
@@ -26,9 +27,7 @@ int vp_legacy_probe(struct virtio_pci_legacy_device *ldev)
 		return -ENODEV;
 
 	rc = dma_set_mask(&pci_dev->dev, DMA_BIT_MASK(64));
-	if (rc) {
-		rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(32));
-	} else {
+	if (!rc) {
 		/*
 		 * The virtio ring base address is expressed as a 32-bit PFN,
 		 * with a page size of 1 << VIRTIO_PCI_QUEUE_ADDR_SHIFT.
@@ -38,7 +37,7 @@ int vp_legacy_probe(struct virtio_pci_legacy_device *ldev)
 	}
 
 	if (rc)
-		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
+		dev_warn(&pci_dev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
 
 	rc = pci_request_region(pci_dev, 0, "virtio-pci-legacy");
 	if (rc)
diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
index e8b3ff2b9fbc..830dc269d68f 100644
--- a/drivers/virtio/virtio_pci_modern_dev.c
+++ b/drivers/virtio/virtio_pci_modern_dev.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <linux/virtio_pci_modern.h>
+#include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 
@@ -256,10 +257,7 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
 
 	err = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
 	if (err)
-		err = dma_set_mask_and_coherent(&pci_dev->dev,
-						DMA_BIT_MASK(32));
-	if (err)
-		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
+		dev_warn(&pci_dev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
 
 	/* Device capability is only mandatory for devices that have
 	 * device-specific configuration.
-- 
2.32.0