Hi Piotr,
On Wed, May 10, 2017 at 01:30:01PM +0100, Piotr Gregor wrote:
> The check for interrupt masking support is done by reading
> the PCI_COMMAND config word
>
> pci_read_config_word(dev, PCI_COMMAND, &orig);
>
> then flipping the PCI_COMMAND_INTX_DISABLE bit and writing result back
>
> pci_write_config_word(dev, PCI_COMMAND,
> orig ^ PCI_COMMAND_INTX_DISABLE);
>
> The expected result is that following read of the PCI_COMMAND
>
> pci_read_config_word(dev, PCI_COMMAND, &new);
>
> returns PCI_COMMAND with only PCI_COMMAND_INTX_DISABLE bit changed.
>
> There are two possible outcomes:
>
> 1. Command is the same (hasn't changed)
> 2. Commmand has changed
>
> And the second of them may be decoupled to:
>
> 2.1 Command changed only for PCI_COMMAND_INTX_DISABLE bit
> (hasn't changed for bits different than PCI_COMMAND_INTX_DISABLE)
> 2.2 Command changed for bit(s) different than PCI_COMMAND_INTX_DISABLE bit
> (and maybe for PCI_COMMAND_INTX_DISABLE too)
>
> The 2.1 is expected result and anything else is error.
> The 2.2 outcome is handled by pci_intx_mask_supported by printing
> appropriate message to the log, but outcome 1 is not handled.
>
> Log the message about command not being changed at all.
>
> Signed-off-by: Piotr Gregor <piotrgregor@xxxxxxxxxxx>
> ---
> drivers/pci/pci.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b01bd5b..67a611e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3712,7 +3712,7 @@ EXPORT_SYMBOL_GPL(pci_intx);
> * pci_intx_mask_supported - probe for INTx masking support
> * @dev: the PCI device to operate on
> *
> - * Check if the device dev support INTx masking via the config space
> + * Check if the device dev supports INTx masking via the config space
> * command word.
> */
> bool pci_intx_mask_supported(struct pci_dev *dev)
> @@ -3736,11 +3736,21 @@ bool pci_intx_mask_supported(struct pci_dev *dev)
> * go ahead and check it.
> */
> if ((new ^ orig) & ~PCI_COMMAND_INTX_DISABLE) {
> + /*
> + * If anything else than PCI_COMMAND_INTX_DISABLE bit has
> + * changed (and maybe PCI_COMMAND_INTX_DISABLE too)
> + */
> dev_err(&dev->dev, "Command register changed from 0x%x to 0x%x: driver or hardware bug?\n",
> orig, new);
> } else if ((new ^ orig) & PCI_COMMAND_INTX_DISABLE) {
> + /*
> + * OK. Only PCI_COMMAND_INTX_DISABLE bit has changed
> + */
> mask_supported = true;
> pci_write_config_word(dev, PCI_COMMAND, orig);
> + } else {
> + dev_err(&dev->dev, "Command register hasn't changed when written from 0x%x to 0x%x: driver or hardware bug?\n",
> + orig, new);
Bit 10 was a reserved bit in PCI r2.2 and was defined as
PCI_COMMAND_INTX_DISABLE in r2.3 of the spec, so I don't think we
should treat this as an error.
> }
>
> pci_cfg_access_unlock(dev);
> @@ -3798,7 +3808,7 @@ static bool pci_check_and_set_intx_mask(struct pci_dev *dev, bool mask)
> * @dev: the PCI device to operate on
> *
> * Check if the device dev has its INTx line asserted, mask it and
> - * return true in that case. False is returned if not interrupt was
> + * return true in that case. False is returned if interrupt wasn't
> * pending.
> */
> bool pci_check_and_mask_intx(struct pci_dev *dev)
> --
> 2.1.4
>
