From: Huacai Chen chenhuacai@loongson.cn
[ Upstream commit 8b3517f88ff2983f52698893519227c10aac90b2 ]
Except for isochronous-configured devices, software may set Max_Read_Request_Size (MRRS) to any value up to 4096. If a device issues a read request with size greater than the completer's Max_Payload_Size (MPS), the completer is required to break the response into multiple completions.
Instead of correctly responding with multiple completions to a large read request, some LS7A Root Ports respond with a Completer Abort. To prevent this, the MRRS must be limited to an implementation-specific value.
The OS cannot detect that value, so rely on BIOS to configure MRRS before booting, and quirk the Root Ports so we never set an MRRS larger than that BIOS value for any downstream device.
N.B. Hot-added devices are not configured by BIOS, and they power up with MRRS = 512 bytes, so these devices will be limited to 512 bytes. If the LS7A limit is smaller, those hot-added devices may not work correctly, but per [1], hotplug is not supported with this chipset revision.
[1] https://lore.kernel.org/r/073638a7-ae68-2847-ac3d-29e5e760d6af@loongson.cn
[bhelgaas: commit log] Link: https://bugzilla.kernel.org/show_bug.cgi?id=216884 Link: https://lore.kernel.org/r/20230201043018.778499-3-chenhuacai@loongson.cn Signed-off-by: Huacai Chen chenhuacai@loongson.cn Signed-off-by: Bjorn Helgaas bhelgaas@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/pci/controller/pci-loongson.c | 44 +++++++++------------------ drivers/pci/pci.c | 10 ++++++ include/linux/pci.h | 1 + 3 files changed, 26 insertions(+), 29 deletions(-)
diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c index 05c50408f13b7..759ec211c17bf 100644 --- a/drivers/pci/controller/pci-loongson.c +++ b/drivers/pci/controller/pci-loongson.c @@ -75,37 +75,23 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON, DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON, DEV_LS7A_LPC, system_bus_quirk);
-static void loongson_mrrs_quirk(struct pci_dev *dev) +static void loongson_mrrs_quirk(struct pci_dev *pdev) { - struct pci_bus *bus = dev->bus; - struct pci_dev *bridge; - static const struct pci_device_id bridge_devids[] = { - { PCI_VDEVICE(LOONGSON, DEV_PCIE_PORT_0) }, - { PCI_VDEVICE(LOONGSON, DEV_PCIE_PORT_1) }, - { PCI_VDEVICE(LOONGSON, DEV_PCIE_PORT_2) }, - { 0, }, - }; - - /* look for the matching bridge */ - while (!pci_is_root_bus(bus)) { - bridge = bus->self; - bus = bus->parent; - /* - * Some Loongson PCIe ports have a h/w limitation of - * 256 bytes maximum read request size. They can't handle - * anything larger than this. So force this limit on - * any devices attached under these ports. - */ - if (pci_match_id(bridge_devids, bridge)) { - if (pcie_get_readrq(dev) > 256) { - pci_info(dev, "limiting MRRS to 256\n"); - pcie_set_readrq(dev, 256); - } - break; - } - } + /* + * Some Loongson PCIe ports have h/w limitations of maximum read + * request size. They can't handle anything larger than this. So + * force this limit on any devices attached under these ports. + */ + struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->bus); + + bridge->no_inc_mrrs = 1; } -DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, loongson_mrrs_quirk); +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON, + DEV_PCIE_PORT_0, loongson_mrrs_quirk); +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON, + DEV_PCIE_PORT_1, loongson_mrrs_quirk); +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON, + DEV_PCIE_PORT_2, loongson_mrrs_quirk);
static void loongson_pci_pin_quirk(struct pci_dev *pdev) { diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 5641786bd0206..aee2c9dd2ddca 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -6026,6 +6026,7 @@ int pcie_set_readrq(struct pci_dev *dev, int rq) { u16 v; int ret; + struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
if (rq < 128 || rq > 4096 || !is_power_of_2(rq)) return -EINVAL; @@ -6044,6 +6045,15 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
v = (ffs(rq) - 8) << 12;
+ if (bridge->no_inc_mrrs) { + int max_mrrs = pcie_get_readrq(dev); + + if (rq > max_mrrs) { + pci_info(dev, "can't set Max_Read_Request_Size to %d; max is %d\n", rq, max_mrrs); + return -EINVAL; + } + } + ret = pcie_capability_clear_and_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_READRQ, v);
diff --git a/include/linux/pci.h b/include/linux/pci.h index 254c8a4126a89..50042ea8e0083 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -572,6 +572,7 @@ struct pci_host_bridge { void *release_data; unsigned int ignore_reset_delay:1; /* For entire hierarchy */ unsigned int no_ext_tags:1; /* No Extended Tags */ + unsigned int no_inc_mrrs:1; /* No Increase MRRS */ unsigned int native_aer:1; /* OS may use PCIe AER */ unsigned int native_pcie_hotplug:1; /* OS may use PCIe hotplug */ unsigned int native_shpc_hotplug:1; /* OS may use SHPC hotplug */