[PATCH 4/4] Avoid DMA exception when using axon_msi with IOMMU

[Michael Ellerman]

There's a brown-paper-bag bug in axon_msi, we pass the address of our
FIFO directly to the hardware, without DMA mapping it. This leads to
DMA exceptions if you enable MSI & the IOMMU.

The fix is to correctly DMA map the fifo, dma_alloc_coherent() does
what we want - and we need to track the virt & phys addresses.

Signed-off-by: Michael Ellerman <[EMAIL PROTECTED]>
---
 arch/powerpc/platforms/cell/axon_msi.c |   21 ++++++++++-----------
 1 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/platforms/cell/axon_msi.c 
b/arch/powerpc/platforms/cell/axon_msi.c
index ea3dc8c..b9a97c4 100644
--- a/arch/powerpc/platforms/cell/axon_msi.c
+++ b/arch/powerpc/platforms/cell/axon_msi.c
@@ -65,7 +65,8 @@
 
 struct axon_msic {
        struct irq_host *irq_host;
-       __le32 *fifo;
+       __le32 *fifo_virt;
+       dma_addr_t fifo_phys;
        dcr_host_t dcr_host;
        u32 read_offset;
 };
@@ -91,7 +92,7 @@ static void axon_msi_cascade(unsigned int irq, struct 
irq_desc *desc)
 
        while (msic->read_offset != write_offset) {
                idx  = msic->read_offset / sizeof(__le32);
-               msi  = le32_to_cpu(msic->fifo[idx]);
+               msi  = le32_to_cpu(msic->fifo_virt[idx]);
                msi &= 0xFFFF;
 
                pr_debug("axon_msi: woff %x roff %x msi %x\n",
@@ -306,7 +307,6 @@ static int axon_msi_shutdown(struct of_device *device)
 static int axon_msi_probe(struct of_device *device,
                          const struct of_device_id *device_id)
 {
-       struct page *page;
        struct device_node *dn = device->node;
        struct axon_msic *msic;
        unsigned int virq;
@@ -338,16 +338,14 @@ static int axon_msi_probe(struct of_device *device,
                goto out_free_msic;
        }
 
-       page = alloc_pages_node(of_node_to_nid(dn), GFP_KERNEL,
-                               get_order(MSIC_FIFO_SIZE_BYTES));
-       if (!page) {
+       msic->fifo_virt = dma_alloc_coherent(&device->dev, MSIC_FIFO_SIZE_BYTES,
+                                            &msic->fifo_phys, GFP_KERNEL);
+       if (!msic->fifo_virt) {
                printk(KERN_ERR "axon_msi: couldn't allocate fifo for %s\n",
                       dn->full_name);
                goto out_free_msic;
        }
 
-       msic->fifo = page_address(page);
-
        msic->irq_host = irq_alloc_host(of_node_get(dn), IRQ_HOST_MAP_NOMAP,
                                        NR_IRQS, &msic_host_ops, 0);
        if (!msic->irq_host) {
@@ -370,9 +368,9 @@ static int axon_msi_probe(struct of_device *device,
        pr_debug("axon_msi: irq 0x%x setup for axon_msi\n", virq);
 
        /* Enable the MSIC hardware */
-       msic_dcr_write(msic, MSIC_BASE_ADDR_HI_REG, (u64)msic->fifo >> 32);
+       msic_dcr_write(msic, MSIC_BASE_ADDR_HI_REG, msic->fifo_phys >> 32);
        msic_dcr_write(msic, MSIC_BASE_ADDR_LO_REG,
-                                 (u64)msic->fifo & 0xFFFFFFFF);
+                                 msic->fifo_phys & 0xFFFFFFFF);
        msic_dcr_write(msic, MSIC_CTRL_REG,
                        MSIC_CTRL_IRQ_ENABLE | MSIC_CTRL_ENABLE |
                        MSIC_CTRL_FIFO_SIZE);
@@ -390,7 +388,8 @@ static int axon_msi_probe(struct of_device *device,
 out_free_host:
        kfree(msic->irq_host);
 out_free_fifo:
-       __free_pages(virt_to_page(msic->fifo), get_order(MSIC_FIFO_SIZE_BYTES));
+       dma_free_coherent(&device->dev, MSIC_FIFO_SIZE_BYTES, msic->fifo_virt,
+                         msic->fifo_phys);
 out_free_msic:
        kfree(msic);
 out:
-- 
1.5.2.rc1.1884.g59b20

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