diff options
Diffstat (limited to 'arch/x86/kernel/amd_nb.c')
| -rw-r--r-- | arch/x86/kernel/amd_nb.c | 44 |
1 files changed, 39 insertions, 5 deletions
diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c index 027a8c7a2c9e..059e5c16af05 100644 --- a/arch/x86/kernel/amd_nb.c +++ b/arch/x86/kernel/amd_nb.c @@ -180,6 +180,43 @@ static struct pci_dev *next_northbridge(struct pci_dev *dev, return dev; } +/* + * SMN accesses may fail in ways that are difficult to detect here in the called + * functions amd_smn_read() and amd_smn_write(). Therefore, callers must do + * their own checking based on what behavior they expect. + * + * For SMN reads, the returned value may be zero if the register is Read-as-Zero. + * Or it may be a "PCI Error Response", e.g. all 0xFFs. The "PCI Error Response" + * can be checked here, and a proper error code can be returned. + * + * But the Read-as-Zero response cannot be verified here. A value of 0 may be + * correct in some cases, so callers must check that this correct is for the + * register/fields they need. + * + * For SMN writes, success can be determined through a "write and read back" + * However, this is not robust when done here. + * + * Possible issues: + * + * 1) Bits that are "Write-1-to-Clear". In this case, the read value should + * *not* match the write value. + * + * 2) Bits that are "Read-as-Zero"/"Writes-Ignored". This information cannot be + * known here. + * + * 3) Bits that are "Reserved / Set to 1". Ditto above. + * + * Callers of amd_smn_write() should do the "write and read back" check + * themselves, if needed. + * + * For #1, they can see if their target bits got cleared. + * + * For #2 and #3, they can check if their target bits got set as intended. + * + * This matches what is done for RDMSR/WRMSR. As long as there's no #GP, then + * the operation is considered a success, and the caller does their own + * checking. + */ static int __amd_smn_rw(u16 node, u32 address, u32 *value, bool write) { struct pci_dev *root; @@ -202,9 +239,6 @@ static int __amd_smn_rw(u16 node, u32 address, u32 *value, bool write) err = (write ? pci_write_config_dword(root, 0x64, *value) : pci_read_config_dword(root, 0x64, value)); - if (err) - pr_warn("Error %s SMN address 0x%x.\n", - (write ? "writing to" : "reading from"), address); out_unlock: mutex_unlock(&smn_mutex); @@ -213,7 +247,7 @@ out: return err; } -int amd_smn_read(u16 node, u32 address, u32 *value) +int __must_check amd_smn_read(u16 node, u32 address, u32 *value) { int err = __amd_smn_rw(node, address, value, false); @@ -226,7 +260,7 @@ int amd_smn_read(u16 node, u32 address, u32 *value) } EXPORT_SYMBOL_GPL(amd_smn_read); -int amd_smn_write(u16 node, u32 address, u32 value) +int __must_check amd_smn_write(u16 node, u32 address, u32 value) { return __amd_smn_rw(node, address, &value, true); } |