Re: [PATCH v4] pci: Make return value of pcie_capability_read*() consistent

[Yicong Yang]

On 2020/4/28 2:13, Bjorn Helgaas wrote:
>
> I'm starting to think we're approaching this backwards.  I searched
> for PCIBIOS_FUNC_NOT_SUPPORTED, PCIBIOS_BAD_VENDOR_ID, and the other
> error values.  Almost every use is a *return* in a config accessor.
> There are very, very few *tests* for these values.

If we have certain reasons to reserve PCI_BIOS* error to identify PCI errors
in PCI drivers, maybe redefine the PCI_BIOS* to generic error codes can solve
the issues, and no need to call pcibios_err_to_errno() to do the conversion.
Few changes may be made to current codes. One possible patch may
look like below. Otherwise, maybe convert all PCI_BIOS* errors to generic error
codes is a better idea.

Not sure it's the best way or not. Just FYI.


diff --git a/include/linux/pci.h b/include/linux/pci.h
index 83ce1cd..843987c 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -675,14 +675,18 @@ static inline bool pci_dev_msi_enabled(struct pci_dev *pci_dev) { return false;
 
 /* Error values that may be returned by PCI functions */
 #define PCIBIOS_SUCCESSFUL		0x00
-#define PCIBIOS_FUNC_NOT_SUPPORTED	0x81
-#define PCIBIOS_BAD_VENDOR_ID		0x83
-#define PCIBIOS_DEVICE_NOT_FOUND	0x86
-#define PCIBIOS_BAD_REGISTER_NUMBER	0x87
-#define PCIBIOS_SET_FAILED		0x88
-#define PCIBIOS_BUFFER_TOO_SMALL	0x89
-
-/* Translate above to generic errno for passing back through non-PCI code */
+#define PCIBIOS_FUNC_NOT_SUPPORTED	-ENOENT
+#define PCIBIOS_BAD_VENDOR_ID		-ENOTTY
+#define PCIBIOS_DEVICE_NOT_FOUND	-ENODEV
+#define PCIBIOS_BAD_REGISTER_NUMBER	-EFAULT
+#define PCIBIOS_SET_FAILED		-EIO
+#define PCIBIOS_BUFFER_TOO_SMALL	-ENOSPC
+
+/**
+ * Translate above to generic errno for passing back through non-PCI code
+ *
+ * Deprecated. Use the PCIBIOS_* directly without a translation.
+ */
 static inline int pcibios_err_to_errno(int err)
 {
 	if (err <= PCIBIOS_SUCCESSFUL)
@@ -690,17 +694,12 @@ static inline int pcibios_err_to_errno(int err)
 
 	switch (err) {
 	case PCIBIOS_FUNC_NOT_SUPPORTED:
-		return -ENOENT;
 	case PCIBIOS_BAD_VENDOR_ID:
-		return -ENOTTY;
 	case PCIBIOS_DEVICE_NOT_FOUND:
-		return -ENODEV;
 	case PCIBIOS_BAD_REGISTER_NUMBER:
-		return -EFAULT;
 	case PCIBIOS_SET_FAILED:
-		return -EIO;
 	case PCIBIOS_BUFFER_TOO_SMALL:
-		return -ENOSPC;
+		return err;
 	}
 
 	return -ERANGE;


>
> For example, the only tests for PCIBIOS_FUNC_NOT_SUPPORTED are in
> xen_pcibios_err_to_errno() and pcibios_err_to_errno(), i.e., we're
> just converting that value to -ENOENT or the Xen-specific thing.
>
> So I think the best approach might be to remove the PCIBIOS_* error
> values completely and replace them with the corresponding values from
> pcibios_err_to_errno().  For example, a part of the patch would look
> like this:
>
> diff --git a/arch/mips/pci/ops-emma2rh.c b/arch/mips/pci/ops-emma2rh.c
> index 65f47344536c..d4d9c902c147 100644
> --- a/arch/mips/pci/ops-emma2rh.c
> +++ b/arch/mips/pci/ops-emma2rh.c
> @@ -100,7 +100,7 @@ static int pci_config_read(struct pci_bus *bus, unsigned int devfn, int where,
>  		break;
>  	default:
>  		emma2rh_out32(EMMA2RH_PCI_IWIN0_CTR, backup_win0);
> -		return PCIBIOS_FUNC_NOT_SUPPORTED;
> +		return -ENOENT;
>  	}
>  
>  	emma2rh_out32(EMMA2RH_PCI_IWIN0_CTR, backup_win0);
> @@ -149,7 +149,7 @@ static int pci_config_write(struct pci_bus *bus, unsigned int devfn, int where,
>  		break;
>  	default:
>  		emma2rh_out32(EMMA2RH_PCI_IWIN0_CTR, backup_win0);
> -		return PCIBIOS_FUNC_NOT_SUPPORTED;
> +		return -ENOENT;
>  	}
>  	*(volatile u32 *)(base + (PCI_FUNC(devfn) << 8) +
>  			  (where & 0xfffffffc)) = data;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 83ce1cdf5676..f95637a8d391 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -675,7 +675,6 @@ static inline bool pci_dev_msi_enabled(struct pci_dev *pci_dev) { return false;
>  
>  /* Error values that may be returned by PCI functions */
>  #define PCIBIOS_SUCCESSFUL		0x00
> -#define PCIBIOS_FUNC_NOT_SUPPORTED	0x81
>  #define PCIBIOS_BAD_VENDOR_ID		0x83
>  #define PCIBIOS_DEVICE_NOT_FOUND	0x86
>  #define PCIBIOS_BAD_REGISTER_NUMBER	0x87
> @@ -689,8 +688,6 @@ static inline int pcibios_err_to_errno(int err)
>  		return err; /* Assume already errno */
>  
>  	switch (err) {
> -	case PCIBIOS_FUNC_NOT_SUPPORTED:
> -		return -ENOENT;
>  	case PCIBIOS_BAD_VENDOR_ID:
>  		return -ENOTTY;
>  	case PCIBIOS_DEVICE_NOT_FOUND:
> .
>