Re: [PATCH] OF: PCI: const usage needed by MIPS

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, May 1, 2012 at 7:28 AM, John Crispin <blogic@openwrt.org> wrote:
> On 30/04/12 19:54, David Daney wrote:
>> On 04/30/2012 10:46 AM, John Crispin wrote:
>>> On MIPS we want to call of_irq_map_pci from inside
>>>
>>> arch/mips/include/asm/pci.h:extern int pcibios_map_irq(
>>>                 const struct pci_dev *dev, u8 slot, u8 pin);
>>>
>>> For this to work we need to change several functions to const usage.
>>
>> I think there is a mismatch on this throughout the kernel.
>>
>> Properly fixing it requires touching many more places than these.
>> Although I haven't tried it, I wouldn't be surprised if doing this
>> caused warnings to appear in non-MIPS code.
>>
>> Ralf had a patch at one point that tried to make this consistent
>> tree-wide, but it is not yet applied.
>>
>> David Daney
>
> Hi,
>
> Ok, lets see what Ralf has to say.
>
> I just tested the patch on x86 with OF enabled and drivers turned on
> that use the API. I did not see any errors appear.

I'm far from a const expert, but I think this should be safe.  Here's
my reasoning:

We're changing pci_swizzle_interrupt_pin() to take a pointer to a
constant struct pci_dev.  pci_swizzle_interrupt_pin() only reads the
struct pci_dev; it doesn't modify it.  It is legal to pass either
"struct pci_dev *" or "const struct pci_dev *" to a function expecting
"const struct pci_dev *"; the callee just won't be able to modify the
struct, even if the caller can.

Similar reasoning applies to of_irq_map_pci().

So I'm fine with this.  You sent it to Grant, so I'll assume he'll
merge it unless I hear otherwise.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>