Subject: [PATCH] arm64: pci: add support for pci_mmap_page_range

From: [email-masked] (Jerin Jacob)
Date: Mon, 27 Jul 2015 10:40:29 +0530

On Fri, Jul 24, 2015 at 03:41:03PM +0100, Will Deacon wrote:
> On Fri, Jul 24, 2015 at 06:54:23AM +0100, Jerin Jacob wrote:
> > certain X11 servers and user space network drivers frameworks
> > need PCI mmaped /sys/bus/pci/devices/B:D:F/resourceX file to access PCI bar
> > address space from user space.
> > 
> > Signed-off-by: Jerin Jacob <[email-masked]>
> > ---
> >  arch/arm64/include/asm/pci.h |  6 ++++++
> >  arch/arm64/kernel/pci.c      | 20 ++++++++++++++++++++
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
> > index b008a72..e7afe8d 100644
> > --- a/arch/arm64/include/asm/pci.h
> > +++ b/arch/arm64/include/asm/pci.h
> > @@ -39,5 +39,11 @@ static inline int pci_proc_domain(struct pci_bus *bus)
> >  }
> >  #endif  /* CONFIG_PCI */
> >  
> > +#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);
> > +
> > +
> >  #endif  /* __KERNEL__ */
> >  #endif  /* __ASM_PCI_H */
> > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > index 4095379..94b04c7 100644
> > --- a/arch/arm64/kernel/pci.c
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -71,3 +71,23 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> >  	return NULL;
> >  }
> >  #endif
> > +
> > +int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> > +		enum pci_mmap_state mmap_state, int write_combine)
> > +{
> > +	/*
> > +	* I/O space can be accessed via normal processor loads and stores on
> > +	* this platform but for now we elect not to do this and portable
> > +	* drivers should not do this anyway.
> > +	*/
> > +	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);
> > +
> > +	return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> > +	       vma->vm_end - vma->vm_start, vma->vm_page_prot);
> > +}
> 
> So pci_iomap_range chooses the memory attributes based on the BAR flags
> (and even then it looks weird -- CACHEABLE => ioremap, else ioremap_nocache,
> which is just the same as ioremap on arm64).
> 
> It would be good to understand (a) why this is different and (b) what

AFAIU, pci_iomap_range is the generic implementation and chooses to
use only minimal attributes that works on all the architectures.
The primary consumer of pci_iomap_range is virtio_pci driver,Which
doesn't care about HW PCI memory attributes like Prefetchable.

> the consistent set of attributes should be.

PCI perspective, memory attributes are Prefetchable and non-Prefetchable
for a given BAR.

Former one does have read side-effects or supports write
merging(typically used
by graphics memory) and latter one has read side effects and does not
support write merging(typically used by register files)

IMO, In armv8 nomenclature, MT_NORMAL_NC and MT_DEVICE_nGnRnE map
correctly to above PCI memory attribute definitions.

and pci-sysfs.c(consumer of pci_mmap_page_range)
creates the /sys/bus/pci/devices/B:D:F/resource[_wc]X file based
on BAR flag(Prefetchable or non-Prefetchable) and expose to userspace.

Jerin

> Will