> -----Original Message----- > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: 15 September 2016 13:25 > To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: Gabriele Paoloni; devicetree@xxxxxxxxxxxxxxx; > lorenzo.pieralisi@xxxxxxx; minyard@xxxxxxx; linux-pci@xxxxxxxxxxxxxxx; > gregkh@xxxxxxxxxxxxxxxxxxx; John Garry; will.deacon@xxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; Yuanzhichang; Linuxarm; xuwei (O); linux- > serial@xxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > zourongrong@xxxxxxxxx; liviu.dudau@xxxxxxx; kantyzc@xxxxxxx; > zhichang.yuan02@xxxxxxxxx > Subject: Re: [PATCH V3 2/4] ARM64 LPC: LPC driver implementation on > Hip06 > > On Thursday, September 15, 2016 12:05:51 PM CEST Gabriele Paoloni > wrote: > > > -----Original Message----- > > > On Thursday, September 15, 2016 8:02:27 AM CEST Gabriele Paoloni > wrote: > > > > > > > > From <<3.1.1. Open Firmware Properties for Bus Nodes>> in > > > > http://www.firmware.org/1275/bindings/isa/isa0_4d.ps > > > > > > > > I quote: > > > > "There shall be an entry in the "ranges" property for each > > > > of the Memory and/or I/O spaces if that address space is > > > > mapped through the bridge." > > > > > > > > It seems to me that it is ok to have 1:1 address mapping and that > > > > therefore of_translate_address() should fail if "ranges" is not > > > > present. > > > > > > The key here is the definition of "mapped through the bridge". > > > I can only understand this as "directly mapped", i.e. an I/O > > > port of the child bus corresponds directly to a memory address > > > on the parent bus, but this is not the case here. > > > > > > The problem with adding the mapping here is that it looks > > > like it should be valid to create a page table entry for > > > the address returned from the translation and access it through > > > a pointer dereference, but that is clearly not possible. > > > > I understand that somehow we are abusing of the ranges property > > here however the point is that with the current implementation ranges > > is needed because otherwise the ipmi driver probe will fail here: > > > > of_ipmi_probe -> of_address_to_resource -> __of_address_to_resource > > -> of_translate_address -> __of_translate_address > > > > Now we had a bit of discussion internally and to avoid > > having ranges we came up with two possible solutions: > > > > 1) Using bit 3 of phys.hi cell in 2.2.1 of > > http://www.firmware.org/1275/bindings/isa/isa0_4d.ps > > This would mean reworking of_bus_isa_get_flags in > > http://lxr.free-electrons.com/source/drivers/of/address.c#L398 > > and setting a new flag to be checked in __of_address_to_resource > > > > 2) Adding a property in the bindings of each device that is > > a child of our LPC bus and modify __of_address_to_resource > > to check if the property is in the DT and eventually bypass > > of_translate_address > > > > However in both 1) and 2) there are some issues: > > in 1) we are not complying with the isa binding doc (we use > > a bit that should be zero); in 2) we need to modify the > > bindings documentation of the devices that are connected > > to our LPC controller (therefore modifying other devices > > bindings to fit our special case). > > > > I think that maybe having the 1:1 range mapping doesn't > > reflect well the reality but it is the less painful > > solution... > > > > What's your view? > > We can check the 'i' bit for I/O space in of_bus_isa_get_flags, > and that should be enough to translate the I/O port number. > > The only part we need to change here is to not go through > the crazy conversion all the way from PCI I/O space to a > physical address and back to a (logical) port number > that we do today with of_translate_address/pci_address_to_pio. > > I can think of a several of ways to fix __of_address_to_resource > to just do the right thing according to the ISA binding to > make the normal drivers work. > > The easiest solution is probably to hook into the > "taddr == OF_BAD_ADDR" case in __of_address_to_resource > and add a lookup for ISA buses there, and instead check > if some special I/O port operations were registered > for the port number, using an architecture specific > function that arm64 implements. Other architectures > like x86 that don't have a direct mapping between I/O > ports and MMIO addresses would implement that same > function differently. So with respect to this patchset once we enter the "taddr == OF_BAD_ADDR" case you would add an arch specific function that checks if the resource is an I/O resource, if the parent node is an ISA bus (calling of_bus_isa_match) and if arm64_extio_ops is non NULL. I think it can work for us and it doesn't affect current devices. I will talk to Zhichang about this for the next patchset version. Many Thanks for your ideas Gab > > Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
