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    SubjectRe: [PATCH] x86/PCI: sta2x11: use default DMA address translation ops
    Hi Nicolas,

    I'm hoping Christoph will chime in and one of the x86 guys will merge
    this, since I'm not a DMA expert. Trivial comments/questions below.

    On Wed, Oct 16, 2019 at 06:51:37PM +0200, Nicolas Saenz Julienne wrote:
    > The devices found behind this PCIe chip have unusual DMA mapping
    > constraints as there is an AMBA interconnect placed in between them and
    > the different PCI endpoints. The offset between physical memory
    > addresses and AMBA's view is provided by reading a PCI config register,
    > which is saved and used whenever DMA mapping is needed.
    >
    > It turns out that this DMA setup can be represented by properly setting
    > 'dma_pfn_offset', 'dma_bus_mask' and 'dma_mask' during the PCI device
    > enable fixup. And ultimately allows us to get rid of this device's
    > custom DMA functions.
    >
    > Aside from the code deletion and DMA setup, sta2x11_pdev_to_mapping() is
    > moved to avoid warnings whenever CONFIG_PM is not enabled.
    >
    > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

    > - pci_read_config_dword(pdev, AHB_BASE(0), &map->amba_base);
    > +
    > + pci_read_config_dword(pdev, AHB_BASE(0), &amba_base);
    > + dev->dma_pfn_offset = PFN_DOWN(-amba_base);
    > + dev->bus_dma_mask = amba_base + STA2X11_AMBA_SIZE - 1;

    I think of a mask as typically being one less than a power of two, but
    that's not the case here, e.g., STA2X11_AMBA_SIZE - 1 == 0x1fffffff
    (512MB-1), so if amba_size is 1G, the mask will be 0x5fffffff.

    Just double-checking to be sure that's what you intend.

    > + pci_set_consistent_dma_mask(pdev, amba_base + STA2X11_AMBA_SIZE - 1);
    > + pci_set_dma_mask(pdev, amba_base + STA2X11_AMBA_SIZE - 1);

    Maybe add a local variable instead of repeating the "amba_base + ..."
    expression three times?

    > /* Configure AHB mapping */
    > pci_write_config_dword(pdev, AHB_PEXLBASE(0), 0);
    > @@ -252,14 +156,25 @@ static void sta2x11_map_ep(struct pci_dev *pdev)
    > pci_write_config_dword(pdev, AHB_CRW(i), 0);
    >
    > dev_info(&pdev->dev,
    > - "sta2x11: Map EP %i: AMBA address %#8x-%#8x\n",
    > - sta2x11_pdev_to_ep(pdev), map->amba_base,
    > - map->amba_base + STA2X11_AMBA_SIZE - 1);
    > + "sta2x11: Map EP %i: AMBA address %#8x-%#8llx\n",
    > + sta2x11_pdev_to_ep(pdev), amba_base, dev->bus_dma_mask);

    This would read better as

    amba_base, amba_base + STA2X11_AMBA_SIZE - 1

    I know that's the same dev->bus_dma_mask, but a "mask" is not the
    obvious name for the end of a range.

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