linux-kernel - [PATCH v6 2/2] PCI: dwc: Add support for 64-bit MSI target address

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Date:   Thu, 25 Aug 2022 23:54:03 +0000
From:   Will McVicker <willmcvicker@...gle.com>
To:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        "Krzysztof Wilczyński" <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Will McVicker <willmcvicker@...gle.com>
Cc:     kernel-team@...roid.com, Vidya Sagar <vidyas@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Robin Murphy <robin.murphy@....com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: [PATCH v6 2/2] PCI: dwc: Add support for 64-bit MSI target address

Since not all devices require a 32-bit MSI address, add support to the
PCIe host driver to allow setting the DMA mask to 64-bits if the 32-bit
allocation fails. This allows kernels to disable ZONE_DMA32 and bounce
buffering (swiotlb) without risking not being able to get a 32-bit address
during DMA allocation.

Basically, in the slim chance that there are no 32-bit allocations
available, the current PCIe host driver will fail to allocate the msi_msg
page due to a DMA address overflow (seen in [1]). With this patch, the
PCIe host can retry the allocation with a 64-bit DMA mask if the current
PCIe device advertises 64-bit support via its MSI capabilities.

[1] https://lore.kernel.org/all/Yo0soniFborDl7+C@google.com/

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Will McVicker <willmcvicker@...gle.com>
Reviewed-by: Rob Herring <robh@...nel.org>
Acked-by: Jingoo Han <jingoohan1@...il.com>
---
 .../pci/controller/dwc/pcie-designware-host.c | 19 ++++++++++++++++---
 drivers/pci/controller/dwc/pcie-designware.c  |  8 ++++++++
 drivers/pci/controller/dwc/pcie-designware.h  |  1 +
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 39f3b37d4033..7e0352861bcb 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -374,9 +374,22 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 	msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
 					GFP_KERNEL);
 	if (!msi_vaddr) {
-		dev_err(dev, "Failed to alloc and map MSI data\n");
-		dw_pcie_free_msi(pp);
-		return -ENOMEM;
+		u16 msi_capabilities;
+
+		/* Retry the allocation with a 64-bit mask if supported. */
+		msi_capabilities = dw_pcie_msi_capabilities(pci);
+		if ((msi_capabilities & PCI_MSI_FLAGS_ENABLE) &&
+		    (msi_capabilities & PCI_MSI_FLAGS_64BIT)) {
+			dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
+			msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64),
+							&pp->msi_data,
+							GFP_KERNEL);
+		}
+		if (!msi_vaddr) {
+			dev_err(dev, "Failed to alloc and map MSI data\n");
+			dw_pcie_free_msi(pp);
+			return -ENOMEM;
+		}
 	}
 
 	return 0;
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index c6725c519a47..650a7f22f9d0 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -82,6 +82,14 @@ u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap)
 }
 EXPORT_SYMBOL_GPL(dw_pcie_find_capability);
 
+u16 dw_pcie_msi_capabilities(struct dw_pcie *pci)
+{
+	u8 offset;
+
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_MSI);
+	return dw_pcie_readw_dbi(pci, offset + PCI_MSI_FLAGS);
+}
+
 static u16 dw_pcie_find_next_ext_capability(struct dw_pcie *pci, u16 start,
 					    u8 cap)
 {
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index a871ae7eb59e..45fcdfc8c035 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -332,6 +332,7 @@ void dw_pcie_version_detect(struct dw_pcie *pci);
 
 u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap);
 u16 dw_pcie_find_ext_capability(struct dw_pcie *pci, u8 cap);
+u16 dw_pcie_msi_capabilities(struct dw_pcie *pci);
 
 int dw_pcie_read(void __iomem *addr, int size, u32 *val);
 int dw_pcie_write(void __iomem *addr, int size, u32 val);
-- 
2.37.2.672.g94769d06f0-goog