On Wed, Jan 12, 2022 at 12:57:44PM +0000, Jiaxun Yang wrote: > 在2022年1月11日一月 下午9:46，Bjorn Helgaas写道： > > [-cc many, +cc iproc, loongson, tegra maintainers] > > > > On Tue, Jul 21, 2020 at 08:25:14PM -0600, Rob Herring wrote: > >> The majority of DT based host drivers use the default .map_irq() and > >> .swizzle_irq() functions, so let's initialize the function pointers to > >> the default and drop setting them in the host drivers. > >> > >> Drivers like iProc which don't support legacy interrupts need to set > >> .map_irq() back to NULL. > > > > Probably a dumb question... > > > > This patch removed all the ->swizzle_irq users in drivers/pci/, which > > is great -- IIUC swizzling is specified by the PCI-to-PCI Bridge Spec, > > r1.2, sec 9.1, and should not be device-specific. I assume the few > > remaining arch/ users (arm and alpha) are either bugs or workarounds > > for broken devices. > > > > My question is why we still have a few users of ->map_irq: loongson, > > tegra, iproc. Shouldn't this mapping be described somehow via DT? > > For Loongson we are describing IRQ map in DT for newer platforms. > But for legacy platforms (AMD RS780E North Bridge) with i8259 irqchip, > we need to read PCI IRQ registers to get mapping information. > > It is not known until boot time, so we have to use map_irq callback. I see these: Documentation/devicetree/bindings/pci/loongson.yaml arch/mips/boot/dts/loongson/rs780e-pch.dtsi which makes me think there are Loongson systems with DT. Are there some Loongson systems with DT and some legacy ones without? The only driver I see is drivers/pci/controller/pci-loongson.c. Is that used for all Loongson system? It unconditionally uses ->map_irq = loongson_map_irq(). loongson_map_irq() reads PCI_INTERRUPT_LINE; I think that depends on firmware having previously programmed it, right? Bjorn
