Re: [PATCH V3] Revert "PCI: tegra194: Enable support for 256 Byte payload"

Krzysztof Wilczyński
2023-06-27T10:48:22Z

Hello,

> This reverts commit 4fb8e46c1bc4 ("PCI: tegra194: Enable
> support for 256 Byte payload").
>
> Consider a PCIe hierarchy with a PCIe switch and a device connected
> downstream of the switch that has support for MPS which is the minimum in
> the hierarchy, and root port programmed with an MPS in its DevCtl register
> that is greater than the minimum. In this scenario, the default bus
> configuration of the kernel i.e. "PCIE_BUS_DEFAULT" doesn't configure the
> MPS settings in the hierarchy correctly resulting in the device with
> support for minimum MPS in the hierarchy receiving the TLPs of size more
> than that. Although this can be addressed by appending "pci=pcie_bus_safe"
> to the kernel command line, it doesn't seem to be a good idea to always
> have this commandline argument even for the basic functionality to work.
>
> Reverting commit 4fb8e46c1bc4 ("PCI: tegra194: Enable support for 256
> Byte payload") avoids this requirement and ensures that the basic
> functionality of the devices irrespective of the hierarchy and the MPS of
> the devices in the hierarchy.
>
> To reap the benefits of having support for higher MPS, optionally, one can
> always append the kernel command line with "pci=pcie_bus_perf".

Applied to controller/tegra194, thank you!

[1/1] Revert "PCI: tegra194: Enable support for 256 Byte payload"
https://git.kernel.org/pci/pci/c/606295f16360

Krzysztof