Re: [PATCH V3 2/4] ARM64 LPC: LPC driver implementation on Hip06

[Arnd Bergmann <arnd@arndb.de>]

On Friday, September 23, 2016 10:23:30 AM CEST Gabriele Paoloni wrote:
> Hi Arnd
> 
> > -----Original Message-----
> > From: Arnd Bergmann [mailto:arnd@arndb.de]
> > Sent: 23 September 2016 10:52
> > To: zhichang.yuan
> > Cc: Gabriele Paoloni; linux-arm-kernel@lists.infradead.org;
> > devicetree@vger.kernel.org; lorenzo.pieralisi@arm.com; minyard@acm.org;
> > linux-pci@vger.kernel.org; gregkh@linuxfoundation.org; John Garry;
> > will.deacon@arm.com; linux-kernel@vger.kernel.org; Yuanzhichang;
> > Linuxarm; xuwei (O); linux-serial@vger.kernel.org;
> > benh@kernel.crashing.org; zourongrong@gmail.com; liviu.dudau@arm.com;
> > kantyzc@163.com
> > Subject: Re: [PATCH V3 2/4] ARM64 LPC: LPC driver implementation on
> > Hip06
> > 
> > On Friday, September 23, 2016 12:27:17 AM CEST zhichang.yuan wrote:
> > > For this patch sketch, I have a question.
> > > Do we call pci_address_to_pio in arch_of_address_to_pio to get the
> > > corresponding logical IO port
> > > for LPC??
> > 
> > 
> > No, of course not, that would be silly:
> > 
> > The argument to pci_address_to_pio() is a phys_addr_t, and we we don't
> > have one because there is no address associated with your PIO, that
> > is the entire point of your driver!
> > 
> > Also, we already know the mapping because this is what the inb/outb
> > workaround is looking at, so there is absolutely no reason to call it
> > either.
> 
> Ok assume that we do not call pci_address_to_pio() for the ISA bus...
> The LPC driver will register its phys address range in io_range_list,
> then the IPMI driver probe will retrieve its physical address calling
> of_address_to_resource and will use the indirect io to access this
> address.
> 
> From the perspective of the indirect IO function the input parameter
> is an unsigned long addr that (now) can be either:
> 1) an IO token coming from a legacy pci device
> 2) a phys address that lives on the LPC bus
> 
> These are conceptually two separate address spaces (and actually they 
> both start from 0).

Why? Any IORESOURCE_IO address always refers to the logical I/O port
range in Linux, not the physical address that is used on a bus.

> If the input parameter can live on different address spaces that are
> overlapped, even if I save the used LPC range in arm64_extio_ops->start/end
> there is no way for the indirect IO to tell if the input parameter is
> an I/O token or a phys address that belongs to LPC...  

The start address is the offset: if you get an address between 'start'
and 'end', you subtract the 'start' from it, and use that to call
the registered driver function. That works because we can safely
assume that the bus address range that the LPC driver registers starts
zero.

	Arnd