Re: [PATCH v3 20/26] PCI: dwc: Fix dw_pcie_ep_find_capability to return correct capability offset

Bjorn Helgaas
2019-04-13T15:44:43Z

On Mon, Mar 25, 2019 at 03:09:41PM +0530, Kishon Vijay Abraham I wrote:
> commit beb4641a787df79a ("PCI: dwc: Add MSI-X callbacks handler") while
> adding MSI-X callback handler, introduced dw_pcie_ep_find_capability and
> __dw_pcie_ep_find_next_cap for finding the MSI and MSIX capability.
>
> However if MSI or MSIX capability is the last capability (i.e there are
> no additional items in the capabilities list and the Next Capability
> Pointer is set to '0'), __dw_pcie_ep_find_next_cap will return '0'
> even though MSI or MSIX capability may be present. This is because of
> incorrect ordering of "next_cap_ptr" check. Fix it here.

Nice fix. It looks like dw_pcie_ep_find_capability() is currently
only used for MSI and MSI-X, but IIUC, it *could* be used for any
capability, so this commit message seems a little too specific.

It would be slightly less confusing if beb4641a787d ("PCI: dwc: Add
MSI-X callbacks handler") had been split into a commit that added the
general-purpose dw_pcie_ep_find_capability() and a commit that used it
for MSI and MSI-X, but obviously we can't change history.

> Fixes: beb4641a787df79a142 ("PCI: dwc: Add MSI-X callbacks handler")

These commit references are longer than necessary (and different -
19-char SHA1 here and 16 chars above). I typically use 12 chars via

gsr is aliased to `git --no-pager show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"'

> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
> ---
> drivers/pci/controller/dwc/pcie-designware-ep.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index dc6a4bbd3ace..74477ad7467f 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -46,16 +46,19 @@ static u8 __dw_pcie_ep_find_next_cap(struct dw_pcie *pci, u8 cap_ptr,
> u8 cap_id, next_cap_ptr;
> u16 reg;
>
> + if (!cap_ptr)
> + return 0;
> +
> reg = dw_pcie_readw_dbi(pci, cap_ptr);
> - next_cap_ptr = (reg & 0xff00) >> 8;
> cap_id = (reg & 0x00ff);
>
> - if (!next_cap_ptr || cap_id > PCI_CAP_ID_MAX)
> + if (cap_id > PCI_CAP_ID_MAX)
> return 0;
>
> if (cap_id == cap)
> return cap_ptr;
>
> + next_cap_ptr = (reg & 0xff00) >> 8;
> return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
> }
>
> @@ -67,9 +70,6 @@ static u8 dw_pcie_ep_find_capability(struct dw_pcie *pci, u8 cap)
> reg = dw_pcie_readw_dbi(pci, PCI_CAPABILITY_LIST);
> next_cap_ptr = (reg & 0x00ff);
>
> - if (!next_cap_ptr)
> - return 0;
> -
> return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
> }
>
> --
> 2.17.1
>