[PATCH v3] usb: xhci-pci: Limit VIA VL805 DMA addressing to 36 bits

[Xincheng Zhang]

The VIA VL805/806 xHCI controller advertises AC64, but fails to handle
DMA addresses at or above 0x1000000000. On systems with large amounts of
RAM, this can cause USB device failures when the controller is given DMA
addresses beyond its usable address width.

Do not use XHCI_NO_64BIT_SUPPORT for this controller. That quirk clears
the cached AC64 capability and limits DMA to 32 bits, causing unnecessary
bouncing for addresses between 4GiB and 64GiB and hiding the controller's
real AC64 capability from code that may need to distinguish register
access width from usable DMA address width.

Track the usable DMA address width separately from the AC64 capability.
Initialize the generic xhci->dma_mask_bits field to 64 and let PCI quirks
reduce it for controllers with narrower DMA support. Set VIA VL805/806 to
36 bits so the DMA API only hands it addresses in the range it can handle
while keeping HCCPARAMS1.AC64 visible.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Xincheng Zhang <zhangxincheng@xxxxxxxxxxxxx>
---
Changes in v3:
- Replace the dedicated 36-bit quirk bit with generic xhci->dma_mask_bits.
- Let PCI quirks set the usable DMA address width directly.
- Keep the existing 32-bit fallback behavior unchanged.
- Link to v2: https://lore.kernel.org/all/20260629-xhci-via-dma-fix-v2-1-380167319652@xxxxxxxxxxxxx/

Changes in v2:
- Replace XHCI_NO_64BIT_SUPPORT with a dedicated 36-bit DMA mask quirk.
- Preserve HCCPARAMS1.AC64 instead of clearing it for VL805/806.
- Limit VL805/806 DMA to DMA_BIT_MASK(36) instead of 32-bit.
- Add a stable Cc trailer.
- Link to v1: https://lore.kernel.org/all/20260623-xhci-via-dma-fix-v1-1-3f12c81a1cf8@xxxxxxxxxxxxx/
---
 drivers/usb/host/xhci-pci.c |  1 +
 drivers/usb/host/xhci.c     | 15 ++++++++++-----
 drivers/usb/host/xhci.h     |  1 +
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index 039c26b241d0..6b3fcba44b08 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -448,6 +448,7 @@ static void xhci_pci_quirks(struct device *dev, struct xhci_hcd *xhci)
 	if (pdev->vendor == PCI_VENDOR_ID_VIA && pdev->device == PCI_DEVICE_ID_VIA_VL805) {
 		xhci->quirks |= XHCI_LPM_SUPPORT;
 		xhci->quirks |= XHCI_TRB_OVERFETCH;
+		xhci->dma_mask_bits = 36;
 	}
 
 	if (pdev->vendor == PCI_VENDOR_ID_ASMEDIA &&
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 6922cc5496c1..5e6f8f0bb901 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -5457,6 +5457,7 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 	if (xhci->hci_version > 0x100)
 		xhci->hcc_params2 = readl(&xhci->cap_regs->hcc_params2);
 
+	xhci->dma_mask_bits = 64;
 	xhci->max_slots = min(HCS_MAX_SLOTS(hcs_params1), MAX_HC_SLOTS);
 	xhci->max_ports = min(HCS_MAX_PORTS(hcs_params1), MAX_HC_PORTS);
 	/* xhci-plat or xhci-pci might have set max_interrupters already */
@@ -5506,12 +5507,16 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 	if (xhci->quirks & XHCI_NO_64BIT_SUPPORT)
 		xhci->hcc_params &= ~BIT(0);
 
-	/* Set dma_mask and coherent_dma_mask to 64-bits,
-	 * if xHC supports 64-bit addressing */
+	/*
+	 * Set dma_mask and coherent_dma_mask to 64-bits if xHC supports
+	 * 64-bit addressing, unless a controller-specific quirk callback
+	 * limits the usable address width.
+	 */
 	if ((xhci->hcc_params & HCC_64BIT_ADDR) &&
-			!dma_set_mask(dev, DMA_BIT_MASK(64))) {
-		xhci_dbg(xhci, "Enabling 64-bit DMA addresses.\n");
-		dma_set_coherent_mask(dev, DMA_BIT_MASK(64));
+	    !dma_set_mask(dev, DMA_BIT_MASK(xhci->dma_mask_bits))) {
+		xhci_dbg(xhci, "Enabling %u-bit DMA addresses.\n",
+			 xhci->dma_mask_bits);
+		dma_set_coherent_mask(dev, DMA_BIT_MASK(xhci->dma_mask_bits));
 	} else {
 		/*
 		 * This is to avoid error in cases where a 32-bit USB
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index d02046a573e4..2d3941b5e1e3 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1526,6 +1526,7 @@ struct xhci_hcd {
 	/* imod_interval in ns (I * 250ns) */
 	u32		imod_interval;
 	u32		page_size;
+	unsigned int	dma_mask_bits;
 	/* MSI-X/MSI vectors */
 	int		nvecs;
 	/* optional clocks */

---
base-commit: 502d801f0ab03e4f32f9a33d203154ce84887921
change-id: 20260623-xhci-via-dma-fix-c563b889ea54

Best regards,
--  
Xincheng Zhang <zhangxincheng@xxxxxxxxxxxxx>