Messages in this thread | | | Subject | PCI host bridge hotplug test question (was Re: [PATCH v2] bus: hisi_lpc: Don't use devm_kzalloc() to allocate logical PIO range) | From | John Garry <> | Date | Wed, 19 Jun 2019 10:48:32 +0100 |
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On 18/06/2019 18:50, Bjorn Helgaas wrote: > [+cc Rafael, Mika, Jiang, linux-pci for ACPI host bridge hotplug test question] > > On Tue, Jun 18, 2019 at 3:44 AM John Garry <john.garry@huawei.com> wrote: > >>>>> Could you just move the logic_pio_register_range() call farther down >>>>> in hisi_lpc_probe()? IIUC, once logic_pio_register_range() returns, >>>>> an inb() with the right port number will try to access that port, so >>>>> we should be prepared for that, i.e., maybe this in the wrong order to >>>>> begin with? >>>> >>>> No, unfortunately we can't. The reason is that we need the logical PIO >>>> base for that range before we enumerate the children of that host. We >>>> need that base address for "translating" the child bus addresses to >>>> logical PIO addresses. > >>> Ah, yeah, that makes sense. I think. We do assume that we know all >>> the MMIO and I/O port translations before enumerating devices. It's >>> *conceivable* that could be changed someday since we don't actually >>> need the translations until a driver claims the device, >> >> We actually need them before a driver claims the device. >> >> The reason is that when we create that child platform device we set the >> device's IORESOURCE_IO resources according to the translated logic PIO >> addresses, and not the host bus address. This is what makes the host >> transparent to the child device driver. > > I think you need it to set pdev->resource[], which is currently done > long before the driver claims the device (though one could imagine > delaying it even as far as pci_enable_device()-time). I don't think > the translation is actually *used* until the driver claims the device > because only the driver knows how to do any inb/outb to the device. > > But of course, that's all speculative and doesn't change what you need > to do now. The current code assumes we know the translations during > enumeration, so you need to do the logic_pio registration before > enumerating. > >>> and it would >>> gain some flexibility if we didn't have to program the host bridge >>> windows until we know how much space is required. But I don't see >>> that happening anytime soon. > >> My problem is that I need to ensure that the new logical PIO unregister >> function works ok for hot-pluggable host bridges. I need to get some way >> to test this. Advice? >
Hi Bjorn,
> Good question. The ACPI host bridge driver (drivers/acpi/pci_root.c) > should support hotplug, but I'm not sure if there's a manual way to > trigger it via sysfs or something similar. If there is, and you have > a machine with more than one host bridge, you might be able to remove > one that leads to non-essential devices.
For one of our earlier boards I don't think that it had any essential devices on the host bridge. But I need to find out about possibility of removal. Hmmm.
> > Bjorn >
Further to the topic of supporting hotplug and unregistering IO port regions, we don't even release IO port regions in the error path of PCI host enumeration. We have pci_register_io_range(), but no unregister equivalent.
Looking at the history here, pci_register_io_range() was originally in OF code. And in the OF code, calling pci_register_io_range() is a side-effect of parsing the device tree. As such, I can see why there was no unregister function.
It would be worth noting this discussion, where the same was mentioned: https://lore.kernel.org/linux-pci/20180403140410.GE27789@ulmo/
The tegra PCI host probe can defer, but, since there is no tidy-up of pci_register_io_range() when deferring, we need to ensure that the port IO management code can handle re-attempts to register the same range.
It looks like this can be cleaned up also.
Thanks, John
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