PCI: loongson: Override PCIe bridge supported speeds for Loongson-3C6000 series

PCI: loongson: Override PCIe bridge supported speeds for Loongson-3C6000 series

Older steppings of the Loongson-3C6000 series incorrectly report the
supported link speeds on their PCIe bridges (device IDs 0x3c19, 0x3c29)
as only 2.5 GT/s, despite the upstream bus supporting speeds from
2.5 GT/s up to 16 GT/s.

As a result, since commit 774c71c52aa4 ("PCI/bwctrl: Enable only if more
than one speed is supported"), bwctrl will be disabled if there's only
one 2.5 GT/s value in vector 'supported_speeds'.

Manually override the 'supported_speeds' field for affected PCIe bridges
with those found on the upstream bus to correctly reflect the supported
link speeds.  Updating the speeds to reflect what the hardware actually
supports avoids quirks in drivers consuming the speed information.

This commit was originally found from AOSC OS[1].

Fixes: cd89edda4002 ("PCI: loongson: Add ACPI init support")
Signed-off-by: Ayden Meng <aydenmeng@yeah.net>
Signed-off-by: Mingcong Bai <jeffbai@aosc.io>
[Ziyao Li: move from drivers/pci/quirks.c to drivers/pci/controller/pci-loongson.c]
Signed-off-by: Ziyao Li <liziyao@uniontech.com>
[Xi Ruoyao: Fixed falling through logic, added debug log, Fixes tag and rebased to 7.0-rc7]
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
[bhelgaas: commit log, https://lore.kernel.org/all/9d815df3b33a63223112b97440c01247935363c1.camel@xry111.site]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Lain Fearyncess Yang <fsf@live.com>
Tested-by: Ayden Meng <aydenmeng@yeah.net>
Tested-by: Mingcong Bai <jeffbai@aosc.io>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Cc: stable@vger.kernel.org
Link: https://github.com/AOSC-Tracking/linux/commit/4392f441363abdf6fa0a0433d73175a17f493454
Link: https://github.com/AOSC-Tracking/linux/pull/2
Link: https://patch.msgid.link/20260412101731.107059-1-xry111@xry111.site