linux-kernel - Re: [PATCH v8 3/9] pci: Introduce pci_register_io

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Message-ID: <20140701204508.GA19569@bart.dudau.co.uk>
Date:	Tue, 1 Jul 2014 21:45:09 +0100
From:	"Liviu Dudau" <liviu@...au.co.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Liviu Dudau <Liviu.Dudau@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 3/9] pci: Introduce pci_register_io_range() helper
 function.

On Tue, Jul 01, 2014 at 09:36:10PM +0200, Arnd Bergmann wrote:
> On Tuesday 01 July 2014 19:43:28 Liviu Dudau wrote:
> > +/*
> > + * Record the PCI IO range (expressed as CPU physical address + size).
> > + * Return a negative value if an error has occured, zero otherwise
> > + */
> > +int __weak pci_register_io_range(phys_addr_t addr, resource_size_t size)
> > +{
> > +#ifdef PCI_IOBASE
> > +       struct io_range *res;
> > +       resource_size_t allocated_size = 0;
> > +
> > +       /* check if the range hasn't been previously recorded */
> > +       list_for_each_entry(res, &io_range_list, list) {
> > +               if (addr >= res->start && addr + size <= res->start + size)
> > +                       return 0;
> > +               allocated_size += res->size;
> > +       }
> > +
> > +       /* range not registed yet, check for available space */
> > +       if (allocated_size + size - 1 > IO_SPACE_LIMIT)
> > +               return -E2BIG;
> > +
> > +       /* add the range to the list */
> > +       res = kzalloc(sizeof(*res), GFP_KERNEL);
> > +       if (!res)
> > +               return -ENOMEM;
> > +
> > +       res->start = addr;
> > +       res->size = size;
> > +
> > +       list_add_tail(&res->list, &io_range_list);
> > +
> > +       return 0;
> > +#else
> > +       return -EINVAL;
> > +#endif
> > +}
> > +
> >  unsigned long __weak pci_address_to_pio(phys_addr_t address)
> >  {
> > +#ifdef PCI_IOBASE
> > +       struct io_range *res;
> > +       resource_size_t offset = 0;
> > +
> > +       list_for_each_entry(res, &io_range_list, list) {
> > +               if (address >= res->start &&
> > +                       address < res->start + res->size) {
> > +                       return res->start - address + offset;
> > +               }
> > +               offset += res->size;
> > +       }
> > +
> > +       return (unsigned long)-1;
> > +#else
> >         if (address > IO_SPACE_LIMIT)
> >                 return (unsigned long)-1;
> >  
> >         return (unsigned long) address;
> > +#endif
> >  }
> 
> This still conflicts with the other allocator you have in patch 9
> for pci_remap_iospace: nothing guarantees that the mapping is the
> same for both.
> 
> Also, this is a completely pointless exercise at this moment, because
> nobody cares about the result of pci_address_to_pio on architectures
> that don't already provide this function. If we ever get a proper
> Open Firmware implementation that wants to put hardcoded PCI devices
> into DT, we can add an implementation, but for now this seems overkill.
> 
> The allocator in pci_register_io_range seems reasonable, why not merge
> this function with pci_remap_iospace() as I have asked you multiple
> times before? Just make it return the io_offset so the caller can
> put that into the PCI host resources.

Hi Arnd,

While I agree with you that at some moment the allocators were inconsistent
wrt each other, for this version I would respectfully disagree on this.
The allocator in pci_register_io_range() only makes sure that the ranges
are not overlapping, it doesn't do any mapping whatsoever, while
pci_remap_iospace() does only an ioremap_page_range(). The idea is that
you get the offset out of pci_address_to_pio() and apply it to
pci_remap_iospace().

Why do you think there are conflicts?

Best regards,
Liviu


> 
> 	Arnd
> --
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