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Date:   Mon, 2 Dec 2019 09:03:58 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     James Sewart <jamessewart@arista.com>
Cc:     linux-pci@vger.kernel.org, Logan Gunthorpe <logang@deltatee.com>,
        Christoph Hellwig <hch@infradead.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Dmitry Safonov <dima@arista.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Bjorn Helgaas <helgaas@kernel.org>
Subject: Re: [PATCH v5 2/3] PCI: Add parameter nr_devfns to pci_add_dma_alias
Message-ID: <20191202170358.GB4174@infradead.org>
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On Fri, Nov 29, 2019 at 05:56:55PM +0000, James Sewart wrote:
> pci_add_dma_alias can now be used to create a dma alias for a range of
> devfns.
> 
> Signed-off-by: James Sewart <jamessewart@arista.com>
> ---
>  drivers/pci/pci.c    | 23 ++++++++++++++++++-----
>  drivers/pci/quirks.c | 14 +++++++-------
>  include/linux/pci.h  |  2 +-
>  3 files changed, 26 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 0a4449a30ace..f9800a610ca1 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5857,7 +5857,8 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
>  /**
>   * pci_add_dma_alias - Add a DMA devfn alias for a device
>   * @dev: the PCI device for which alias is added
> - * @devfn: alias slot and function
> + * @devfn_from: alias slot and function
> + * @nr_devfns: Number of subsequent devfns to alias
>   *
>   * This helper encodes an 8-bit devfn as a bit number in dma_alias_mask
>   * which is used to program permissible bus-devfn source addresses for DMA
> @@ -5873,8 +5874,14 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
>   * cannot be left as a userspace activity).  DMA aliases should therefore
>   * be configured via quirks, such as the PCI fixup header quirk.
>   */
> -void pci_add_dma_alias(struct pci_dev *dev, u8 devfn)
> +void pci_add_dma_alias(struct pci_dev *dev, u8 devfn_from, unsigned nr_devfns)
>  {
> +	int devfn_to;
> +
> +	if (nr_devfns > U8_MAX+1)
> +		nr_devfns = U8_MAX+1;

Missing whitespaces here as well.  Also this could use max() and I
think you want a documented constants for MAX_NR_DEVFNS that documents
this "not off by one".