On 4/4/2020 12:20 PM, Nicolas Saenz Julienne wrote: > On Thu, 2020-04-02 at 14:38 -0500, Bjorn Helgaas wrote: >> [+cc Rob for DT platform device dependency question] >> >> On Thu, Apr 02, 2020 at 04:27:23PM +0200, Nicolas Saenz Julienne wrote: > > [...] > >>> Sorry it wasn't clear enough, I'll redo this comment. Also note that >>> the PCIe bus and the XHCI chip are hardwired, so that's the only >>> device that'll ever be available on the bus. >>> >>> VIA805's XHCI firmware has to be loaded trough RPi's firmware >>> mailbox in between the PCIe bus probe and the subsequent USB probe. >>> Note that a PCI reset clears the firmware. The only mechanism >>> available in between the two operations are PCI Fixups. These are >>> limited in their own way, as I can't return -EPROBE_DEFER if the >>> firmware interface isn't available yet. Hence the need for an >>> explicit dependency between pcie-brcmstb and raspberrypi's firmware >>> mailbox device. >>> >>> Your concern here showcases this series' limitations. From a high >>> level perspective it's not clear to me who should be responsible for >>> downloading the firmware. >> >> I think it's fairly common for drivers to download firmware to their >> devices. I guess there's not really any need to download the firmware >> until a driver wants to use the device, right? >> >>> And I get the feeling I'm abusing PCI fixups. I haven't found any >>> smart way to deal with this three way dependency of >>> platform/non-platform devices. >> >> So IIUC, the three-way dependency involves: >> >> 1) brcm_pcie_probe(), which initialize the PCI host controller >> platform device, enumerates PCI devices, and makes them available >> for driver binding, > > Yes, and also resets the PCI bus, which will clear VL805's firmware (the XHCI > chip). > >> 2) the firmware mailbox initialization (maybe >> rpi_firmware_probe()?), >> >> 3) quirk_usb_early_handoff(), which downloads firmware to the VL805 >> PCI USB adapter via rpi_firmware_init_vl805(), which uses the >> firmware mailbox? > > And yes, that's the general idea. > >> Is there some way to express a dependency between >> "raspberrypi,bcm2835-firmware" (the platform device claimed by >> rpi_firmware_probe() and "brcm,bcm2711-pcie"? If we could ensure that >> rpi_firmware_probe() runs before brcm_pcie_probe(), would that solve >> part of this? > > That's ultimately what this patch tries to achieve. If there was a way to > offload it to DT it would be way nicer. Have you looked whether device links between producer/consumer could help here? AFAICT there is not usually a way to express an ordering dependency other than by referencing symbols from a different module, which falls apart when everything gets built into the kernel obviously and then you are at the mercy of the linking order and initicall levels. https://www.kernel.org/doc/html/v4.13/driver-api/device_link.html -- Florian
