linux-kernel - Re: [PATCH 1/3] arm64: enable pci resource mapping using sysfs

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Date:   Wed, 15 Mar 2017 17:54:08 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 1/3] arm64: enable pci resource mapping using sysfs

Hi,

On Wed, Mar 15, 2017 at 05:17:46PM +0000, David Woodhouse wrote:
> From: Brijesh Singh <brijess@...zon.com>
> 
> To support pci resource mapping from userspace, pci_mmap_page_range
> implementation must be done for that platform. This support was
> broken for arm64.
> 
> This patch copies existing implementation from arm to
> enable sysfs mmap.

It's not so much "broken" as "not currently supported".

[...]

> +#define HAVE_PCI_MMAP
> +extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> +			       enum pci_mmap_state mmap_state, int write_combine);
> +

Per the prior attempt at this [1], we only want to expose the sysfs
interface, and not the legacy procfs interface, and need the two
decoupled [2].

... or has something changed in the mean time, so that this only exposes
the sysfs interface?

[...]

> +int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> +			enum pci_mmap_state mmap_state, int write_combine)
> +{
> +	if (mmap_state == pci_mmap_io)
> +		return -EINVAL;
> +
> +	if (write_combine)
> +		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +	else
> +		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);

... as per Will's comment in [3], the latter of these should use
pgprot_device.

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-April/421948.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-April/423083.html
[3] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-April/422571.html