linux-kernel - Re: [PATCH v6 2/3] PCI: Add parameter nr_devfns to pci_add_dma

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Message-ID: <20191210223745.GA167002@google.com>
Date:   Tue, 10 Dec 2019 16:37:45 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     James Sewart <jamessewart@...sta.com>
Cc:     linux-pci@...r.kernel.org, Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Dmitry Safonov <dima@...sta.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v6 2/3] PCI: Add parameter nr_devfns to pci_add_dma_alias

[+cc Joerg]

On Tue, Dec 03, 2019 at 03:43:53PM +0000, James Sewart wrote:
> pci_add_dma_alias can now be used to create a dma alias for a range of
> devfns.
> 
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
> Signed-off-by: James Sewart <jamessewart@...sta.com>
> ---
>  drivers/pci/pci.c    | 22 +++++++++++++++++-----
>  drivers/pci/quirks.c | 14 +++++++-------
>  include/linux/pci.h  |  2 +-
>  3 files changed, 25 insertions(+), 13 deletions(-)

Heads up Joerg: I also updated drivers/iommu/amd_iommu.c (this is the
one reported by the kbuild test robot) and removed the printk there
that prints the same thing as the one in pci_add_dma_alias(), and I
updated a PCI quirk that was merged after this patch was posted.

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index d3c83248f3ce..dbb01aceafda 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 +5874,13 @@ 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;
> +
> +	nr_devfns = min(nr_devfns, (unsigned)MAX_NR_DEVFNS);
> +	devfn_to = devfn_from + nr_devfns - 1;

I made this look like:

+       devfn_to = min(devfn_from + nr_devfns - 1,
+                      (unsigned) MAX_NR_DEVFNS - 1);

so devfn_from=0xf0, nr_devfns=0x20 doesn't cause devfn_to to wrap
around.

I did keep Logan's reviewed-by, so let me know if I broke something.

>  	if (!dev->dma_alias_mask)
>  		dev->dma_alias_mask = bitmap_zalloc(MAX_NR_DEVFNS, GFP_KERNEL);
>  	if (!dev->dma_alias_mask) {
> @@ -5882,9 +5888,15 @@ void pci_add_dma_alias(struct pci_dev *dev, u8 devfn)
>  		return;
>  	}
>  
> -	set_bit(devfn, dev->dma_alias_mask);
> -	pci_info(dev, "Enabling fixed DMA alias to %02x.%d\n",
> -		 PCI_SLOT(devfn), PCI_FUNC(devfn));
> +	bitmap_set(dev->dma_alias_mask, devfn_from, nr_devfns);
> +
> +	if (nr_devfns == 1)
> +		pci_info(dev, "Enabling fixed DMA alias to %02x.%d\n",
> +				PCI_SLOT(devfn_from), PCI_FUNC(devfn_from));
> +	else if(nr_devfns > 1)
> +		pci_info(dev, "Enabling fixed DMA alias for devfn range from %02x.%d to %02x.%d\n",
> +				PCI_SLOT(devfn_from), PCI_FUNC(devfn_from),
> +				PCI_SLOT(devfn_to), PCI_FUNC(devfn_to));
>  }