Re: [PATCH v2 1/2] PCI: dwc: ep: Add dw_pcie_ep_hide_ext_capability()

[Niklas Cassel <cassel@kernel.org>]

On Fri, Mar 07, 2025 at 01:47:34PM +0100, Niklas Cassel wrote:
> Add dw_pcie_ep_hide_ext_capability() which can be used by an endpoint
> controller driver to hide a capability.
> 
> This can be useful to hide a capability that is buggy, such that the
> host side does not try to enable the buggy capability.
> 
> Suggested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
>  .../pci/controller/dwc/pcie-designware-ep.c   | 38 +++++++++++++++++++
>  drivers/pci/controller/dwc/pcie-designware.h  |  7 ++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index a8568808b5e5..d671fea1e7c6 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -102,6 +102,44 @@ static u8 dw_pcie_ep_find_capability(struct dw_pcie_ep *ep, u8 func_no, u8 cap)
>  	return __dw_pcie_ep_find_next_cap(ep, func_no, next_cap_ptr, cap);
>  }
>  
> +/**
> + * dw_pcie_ep_hide_ext_capability - Hide a capability from the linked list
> + * @pci: DWC PCI device
> + * @prev_cap: Capability preceding the capability that should be hidden
> + * @cap: Capability that should be hidden
> + *
> + * Return: 0 if success, errno otherwise.
> + */
> +int dw_pcie_ep_hide_ext_capability(struct dw_pcie *pci, u8 prev_cap, u8 cap)
> +{
> +	u16 prev_cap_offset, cap_offset;
> +	u32 prev_cap_header, cap_header;
> +
> +	prev_cap_offset = dw_pcie_find_ext_capability(pci, prev_cap);
> +	if (!prev_cap_offset)
> +		return -EINVAL;
> +
> +	prev_cap_header = dw_pcie_readl_dbi(pci, prev_cap_offset);
> +	cap_offset = PCI_EXT_CAP_NEXT(prev_cap_header);
> +	cap_header = dw_pcie_readl_dbi(pci, cap_offset);
> +
> +	/* cap must immediately follow prev_cap. */
> +	if (PCI_EXT_CAP_ID(cap_header) != cap)
> +		return -EINVAL;
> +
> +	/* Clear next ptr. */
> +	prev_cap_header &= ~GENMASK(31, 20);
> +
> +	/* Set next ptr to next ptr of cap. */
> +	prev_cap_header |= cap_header & GENMASK(31, 20);
> +
> +	dw_pcie_dbi_ro_wr_en(pci);
> +	dw_pcie_writel_dbi(pci, prev_cap_offset, prev_cap_header);
> +	dw_pcie_dbi_ro_wr_dis(pci);
> +
> +	return 0;
> +}

We should have a:
EXPORT_SYMBOL_GPL(dw_pcie_ep_hide_ext_capability);

here too for it to work with PCI EPC drivers that can be built as modules.

Tell me if I should send a v3, or if you can amend this line when applying.


Kind regards,
Niklas