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| author | Pali Rohár <pali@kernel.org> | 2021-11-02 18:12:59 +0100 |
|---|---|---|
| committer | Thomas Bogendoerfer <tsbogend@alpha.franken.de> | 2021-11-03 17:34:11 +0100 |
| commit | 36de23a4c5f0b61ceb4812b535422fa6c6e97447 (patch) | |
| tree | 9fef7f3d525fd8e1e6dcd7ab1b3d19d26e36fb68 /arch/mips/pci | |
| parent | f69fa4c81b426ef07157704ba27e73a42f4911de (diff) | |
| download | lwn-36de23a4c5f0b61ceb4812b535422fa6c6e97447.tar.gz lwn-36de23a4c5f0b61ceb4812b535422fa6c6e97447.zip | |
MIPS: Cobalt: Explain GT64111 early PCI fixup
Properly document why changing PCI Class Code for GT64111 device to Host
Bridge is required as important details were after 20 years forgotten.
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Diffstat (limited to 'arch/mips/pci')
| -rw-r--r-- | arch/mips/pci/fixup-cobalt.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/mips/pci/fixup-cobalt.c b/arch/mips/pci/fixup-cobalt.c index 44be65c3e6bb..00206ff52988 100644 --- a/arch/mips/pci/fixup-cobalt.c +++ b/arch/mips/pci/fixup-cobalt.c @@ -36,6 +36,21 @@ #define VIA_COBALT_BRD_ID_REG 0x94 #define VIA_COBALT_BRD_REG_to_ID(reg) ((unsigned char)(reg) >> 4) +/* + * Default value of PCI Class Code on GT64111 is PCI_CLASS_MEMORY_OTHER (0x0580) + * instead of PCI_CLASS_BRIDGE_HOST (0x0600). Galileo explained this choice in + * document "GT-64111 System Controller for RC4640, RM523X and VR4300 CPUs", + * section "6.5.3 PCI Autoconfiguration at RESET": + * + * Some PCs refuse to configure host bridges if they are found plugged into + * a PCI slot (ask the BIOS vendors why...). The "Memory Controller" Class + * Code does not cause a problem for these non-compliant BIOSes, so we used + * this as the default in the GT-64111. + * + * So fix the incorrect default value of PCI Class Code. More details are on: + * https://lore.kernel.org/r/20211102154831.xtrlgrmrizl5eidl@pali/ + * https://lore.kernel.org/r/20211102150201.GA11675@alpha.franken.de/ + */ static void qube_raq_galileo_early_fixup(struct pci_dev *dev) { if (dev->devfn == PCI_DEVFN(0, 0) && |