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SubjectRe: [PATCH v2 03/24] PCI: Unify PCI error response checking
On Fri, Oct 15, 2021 at 08:08:44PM +0530, Naveen Naidu wrote:
> An MMIO read from a PCI device that doesn't exist or doesn't respond
> causes a PCI error. There's no real data to return to satisfy the
> CPU read, so most hardware fabricates ~0 data.
>
> Use SET_PCI_ERROR_RESPONSE() to set the error response and
> RESPONSE_IS_PCI_ERROR() to check the error response during hardware
> read.
>
> These definitions make error checks consistent and easier to find.
>
> Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>
> ---
> drivers/pci/access.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index b3b2006ed1d2..03712866c818 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -417,10 +417,10 @@ int pcie_capability_read_word(struct pci_dev *dev, int pos, u16 *val)
> ret = pci_read_config_word(dev, pci_pcie_cap(dev) + pos, val);
> /*
> * Reset *val to 0 if pci_read_config_word() fails, it may
> - * have been written as 0xFFFF if hardware error happens
> - * during pci_read_config_word().
> + * have been written as 0xFFFF (PCI_ERROR_RESPONSE) if hardware error
> + * happens during pci_read_config_word().
> */
> - if (ret)
> + if (RESPONSE_IS_PCI_ERROR(val))

What if there is no error (in ret) and the register value was actually
~0? We'd be corrupting the value.

In general, I think we should rely more on the error codes and less on
the ~0 value.

> *val = 0;
> return ret;
> }
> @@ -452,10 +452,10 @@ int pcie_capability_read_dword(struct pci_dev *dev, int pos, u32 *val)
> ret = pci_read_config_dword(dev, pci_pcie_cap(dev) + pos, val);
> /*
> * Reset *val to 0 if pci_read_config_dword() fails, it may
> - * have been written as 0xFFFFFFFF if hardware error happens
> - * during pci_read_config_dword().
> + * have been written as 0xFFFFFFFF (PCI_ERROR_RESPONSE) if hardware
> + * error happens during pci_read_config_dword().
> */
> - if (ret)
> + if (RESPONSE_IS_PCI_ERROR(val))
> *val = 0;
> return ret;
> }
> @@ -529,7 +529,7 @@ EXPORT_SYMBOL(pcie_capability_clear_and_set_dword);
> int pci_read_config_byte(const struct pci_dev *dev, int where, u8 *val)
> {
> if (pci_dev_is_disconnected(dev)) {
> - *val = ~0;
> + SET_PCI_ERROR_RESPONSE(val);
> return PCIBIOS_DEVICE_NOT_FOUND;
> }
> return pci_bus_read_config_byte(dev->bus, dev->devfn, where, val);
> @@ -539,7 +539,7 @@ EXPORT_SYMBOL(pci_read_config_byte);
> int pci_read_config_word(const struct pci_dev *dev, int where, u16 *val)
> {
> if (pci_dev_is_disconnected(dev)) {
> - *val = ~0;
> + SET_PCI_ERROR_RESPONSE(val);
> return PCIBIOS_DEVICE_NOT_FOUND;
> }
> return pci_bus_read_config_word(dev->bus, dev->devfn, where, val);
> @@ -550,7 +550,7 @@ int pci_read_config_dword(const struct pci_dev *dev, int where,
> u32 *val)
> {
> if (pci_dev_is_disconnected(dev)) {
> - *val = ~0;
> + SET_PCI_ERROR_RESPONSE(val);
> return PCIBIOS_DEVICE_NOT_FOUND;
> }
> return pci_bus_read_config_dword(dev->bus, dev->devfn, where, val);
> --
> 2.25.1
>
>

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