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

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2008-01-25 at 16:59 +1100, Michael Ellerman wrote:
> 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 <michael@ellerman.id.au>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> ---
>  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: