On Thu, Apr 17, 2025 at 10:39:49AM +0200, Niklas Cassel wrote: > On Thu, Apr 17, 2025 at 04:07:51PM +0800, Hans Zhang wrote: > > On 2025/4/17 15:48, Niklas Cassel wrote: > > > > Hi Niklas and Shawn, > > > > Thank you very much for your discussion and reply. > > > > I tested it on RK3588 and our platform. By setting pci=pcie_bus_safe, the > > maximum MPS will be automatically matched in the end. > > > > So is my patch no longer needed? For RK3588, does the customer have to > > configure CONFIG_PCIE_BUS_SAFE or pci=pcie_bus_safe? > > > > Also, for pci-meson.c, can the meson_set_max_payload be deleted? > > I think the only reason why this works is because > pcie_bus_configure_settings(), in the case of > pcie_bus_config == PCIE_BUS_SAFE, will walk the bus and set MPS in > the bridge to the lowest of the downstream devices: > https://github.com/torvalds/linux/blob/v6.15-rc2/drivers/pci/probe.c#L2994-L2999 > > So Hans, if you look at lspci for the other RCs/bridges that don't > have any downstream devices connected, do they also show DevCtl.MPS 256B > or do they still show 128B ? > > One could argue that for all policies (execept for maybe PCIE_BUS_TUNE_OFF), > pcie_bus_configure_settings() should start off by initializing DevCtl.MPS to > DevCap.MPS (for the bridge itself), and after that pcie_bus_configure_settings() > can override it depending on policy, e.g. set MPS to 128B in case of > pcie_bus_config == PCIE_BUS_PEER2PEER, or walk the bus in case of > pcie_bus_config == PCIE_BUS_SAFE. > > That way, we should be able to remove the setting for pci-meson.c as well. Thanks, I came here to say basically the same thing. Ideally I think the generic code in pcie_bus_configure_settings() should be able to increase MPS or decrease it such that neither meson_set_max_payload() nor rockchip_pcie_set_max_payload() is required. However, the requirement to pick a Kconfig setting makes it a mess. I would love to get rid of those Kconfig symbols. I don't like the command-line parameters either, but it would definitely be an improvement if we could nuke the Kconfig symbols and rely on the command-line parameters. It's also a problem when devices are hot-added after the hierarchy has already been set up because the new device might not work correctly in the existing config. It's a hard problem to solve. For new platforms without an install base, maybe it would be easier to rely on the command-line parameters since there aren't a bunch of users that would have to change the Kconfig. Bjorn
