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Message-ID: <CAE9FiQXPmG6UYYGHG52_i8vaBJ5yPm6Z4Zfx_BhQxVhyWC5fnw@mail.gmail.com>
Date: Wed, 8 Jun 2016 15:35:16 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
David Miller <davem@...emloft.net>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Wei Yang <weiyang@...ux.vnet.ibm.com>,
Khalid Aziz <khalid.aziz@...cle.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>, linux-cris-kernel@...s.com,
"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
linux-am33-list@...hat.com, linux-parisc@...r.kernel.org,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
linux-sh@...r.kernel.org,
"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v12 01/15] PCI: Let pci_mmap_page_range() take extra
resource pointer
On Wed, Jun 8, 2016 at 2:03 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> Microblaze does look up the resource in pci_mmap_page_range(), but it
> never actually uses it. It *looks* like it uses it, but that code is
> actually dead and I think we should apply the first patch below.
Good one.
>
> That leaves powerpc as the only arch that would use this extra
> resource pointer. It uses it in __pci_mmap_set_pgprot() to help
> decide whether to make a normal uncacheable mapping or a write-
> combining one. There's nothing here that's specific to the powerpc
> architecture, and I don't think we should add this parameter just to
> cater to powerpc.
>
> There are two cases where __pci_mmap_set_pgprot() on powerpc does
> something based on the resource:
>
> 1) We're using procfs to mmap I/O port space after we requested
> write-combining, e.g., we did this:
>
> ioctl(fd, PCIIOC_MMAP_IS_IO); # request I/O port space
> ioctl(fd, PCIIOC_WRITE_COMBINE, 1); # request write-combining
> mmap(fd, ...)
>
> On powerpc, we ignore the write-combining request in this case.
>
> I think we can handle this case by applying the second patch
> below to ignore write-combining on I/O space for all arches, not
> just powerpc.
>
> 2) We're using sysfs to mmap resourceN (not resourceN_wc), and
> the resource is prefetchable. On powerpc, we turn *on*
> write-combining, even though the user didn't ask for it.
>
> I'm not sure this case is actually safe, because it changes the
> ordering properties. If it *is* safe, we could enable write-
> combining in pci_mmap_resource(), where we already have the
> resource and it could be done for all arches.
>
> This case is not strictly necessary, except to avoid a
> performance regression, because the user could have mapped
> resourceN_wc to explicitly request write-combining.
>
Agreed.
>
> commit 4e712b691abc5b579e3e4327f56b0b7988bdd1cb
> Author: Bjorn Helgaas <bhelgaas@...gle.com>
> Date: Wed Jun 8 14:00:14 2016 -0500
>
> microblaze/PCI: Remove useless __pci_mmap_set_pgprot()
>
> The microblaze __pci_mmap_set_pgprot() was apparently copied from powerpc,
> where it computes either an uncacheable pgprot_t or a write-combining one.
> But on microblaze, we always use the regular uncacheable pgprot_t.
>
> Remove the useless code in __pci_mmap_set_pgprot() and inline the
> pgprot_noncached() at the only caller.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> diff --git a/arch/microblaze/pci/pci-common.c b/arch/microblaze/pci/pci-common.c
> index 14cba60..1974567 100644
> --- a/arch/microblaze/pci/pci-common.c
> +++ b/arch/microblaze/pci/pci-common.c
> @@ -219,33 +219,6 @@ static struct resource *__pci_mmap_make_offset(struct pci_dev *dev,
> }
>
> /*
> - * Set vm_page_prot of VMA, as appropriate for this architecture, for a pci
> - * device mapping.
> - */
> -static pgprot_t __pci_mmap_set_pgprot(struct pci_dev *dev, struct resource *rp,
> - pgprot_t protection,
> - enum pci_mmap_state mmap_state,
> - int write_combine)
> -{
> - pgprot_t prot = protection;
> -
> - /* Write combine is always 0 on non-memory space mappings. On
> - * memory space, if the user didn't pass 1, we check for a
> - * "prefetchable" resource. This is a bit hackish, but we use
> - * this to workaround the inability of /sysfs to provide a write
> - * combine bit
> - */
> - if (mmap_state != pci_mmap_mem)
> - write_combine = 0;
> - else if (write_combine == 0) {
> - if (rp->flags & IORESOURCE_PREFETCH)
> - write_combine = 1;
> - }
> -
> - return pgprot_noncached(prot);
> -}
> -
> -/*
> * This one is used by /dev/mem and fbdev who have no clue about the
> * PCI device, it tries to find the PCI device first and calls the
> * above routine
> @@ -317,9 +290,7 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> return -EINVAL;
>
> vma->vm_pgoff = offset >> PAGE_SHIFT;
> - vma->vm_page_prot = __pci_mmap_set_pgprot(dev, rp,
> - vma->vm_page_prot,
> - mmap_state, write_combine);
> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>
> ret = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> vma->vm_end - vma->vm_start, vma->vm_page_prot);
>
Acked-by: Yinghai Lu <yinghai@...nel.org>
>
>
> commit 962972ee5e0ba6ceb680cb182bad65f8886586a6
> Author: Bjorn Helgaas <bhelgaas@...gle.com>
> Date: Wed Jun 8 14:46:54 2016 -0500
>
> PCI: Ignore write-combining when mapping I/O port space
>
> PCI exposes files like /proc/bus/pci/00/00.0 in procfs. These files
> support operations like this:
>
> ioctl(fd, PCIIOC_MMAP_IS_IO); # request I/O port space
> ioctl(fd, PCIIOC_WRITE_COMBINE, 1); # request write-combining
> mmap(fd, ...)
>
> Many architectures don't allow mmap of I/O port space at all, but I don't
> think it makes sense to do a write-combining mapping on the ones that do.
> We could change proc_bus_pci_ioctl() so the user could never enable write-
> combining for I/O port space, but that would break the following sequence,
> which is currently legal:
>
> mmap(fd, ...) # default is I/O, non-combining
> ioctl(fd, PCIIOC_WRITE_COMBINE, 1); # request write-combining
> ioctl(fd, PCIIOC_MMAP_IS_MEM); # request memory space
> mmap(fd, ...)
>
> Ignore the write-combining flag when mapping I/O port space.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index 3f155e7..21f8d613 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -247,7 +247,8 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
>
> ret = pci_mmap_page_range(dev, vma,
> fpriv->mmap_state,
> - fpriv->write_combine);
> + (fpriv->mmap_state == pci_mmap_mem) ?
> + fpriv->write_combine : 0);
> if (ret < 0)
> return ret;
>
ok to me.
At the same time, can you kill __pci_mmap_set_pgprot() for powerpc.
diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index 0f7a60f..0d0148d 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -356,36 +356,6 @@ static struct resource
*__pci_mmap_make_offset(struct pci_dev *dev,
}
/*
- * Set vm_page_prot of VMA, as appropriate for this architecture, for a pci
- * device mapping.
- */
-static pgprot_t __pci_mmap_set_pgprot(struct pci_dev *dev, struct resource *rp,
- pgprot_t protection,
- enum pci_mmap_state mmap_state,
- int write_combine)
-{
-
- /* Write combine is always 0 on non-memory space mappings. On
- * memory space, if the user didn't pass 1, we check for a
- * "prefetchable" resource. This is a bit hackish, but we use
- * this to workaround the inability of /sysfs to provide a write
- * combine bit
- */
- if (mmap_state != pci_mmap_mem)
- write_combine = 0;
- else if (write_combine == 0) {
- if (rp->flags & IORESOURCE_PREFETCH)
- write_combine = 1;
- }
-
- /* XXX would be nice to have a way to ask for write-through */
- if (write_combine)
- return pgprot_noncached_wc(protection);
- else
- return pgprot_noncached(protection);
-}
-
-/*
* This one is used by /dev/mem and fbdev who have no clue about the
* PCI device, it tries to find the PCI device first and calls the
* above routine
@@ -458,9 +428,10 @@ int pci_mmap_page_range(struct pci_dev *dev,
struct vm_area_struct *vma,
return -EINVAL;
vma->vm_pgoff = offset >> PAGE_SHIFT;
- vma->vm_page_prot = __pci_mmap_set_pgprot(dev, rp,
- vma->vm_page_prot,
- mmap_state, write_combine);
+ if (write_combine)
+ vma->vm_page_prot = pgprot_noncached_wc(protection);
+ else
+ vma->vm_page_prot = pgprot_noncached(protection);
ret = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
vma->vm_end - vma->vm_start, vma->vm_page_prot);
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