Re: [PATCH v6 5/9] PCI: dwc: Implement .start_link(), .stop_link() hooks

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Aug 28, 2025 at 05:39:02PM +0530, Krishna Chaitanya Chundru wrote:
> Implement stop_link() and  start_link() function op for dwc drivers.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 952f8594b501254d2b2de5d5e056e16d2aa8d4b7..bcdc4a0e4b4747f2d62e1b67bc1aeda16e35acdd 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -722,10 +722,28 @@ void __iomem *dw_pcie_own_conf_map_bus(struct pci_bus *bus, unsigned int devfn,
>  }
>  EXPORT_SYMBOL_GPL(dw_pcie_own_conf_map_bus);
>  
> +static int dw_pcie_op_start_link(struct pci_bus *bus)
> +{
> +	struct dw_pcie_rp *pp = bus->sysdata;
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +
> +	return dw_pcie_host_start_link(pci);

This takes a pci_bus *, which could be any PCI bus, but this only
works for root buses because it affects the link from a Root Port.

I know the TC9563 is directly below the Root Port in the current
topology, but it seems like the ability to configure a Switch with I2C
or similar is potentially of general interest, even if the switch is
deeper in the hierarchy.

Is there a generic way to inhibit link training, e.g., with the Link
Disable bit in the Link Control register?  If so, this could
potentially be done in a way that would work for any vendor and for
any Downstream Port, including Root Ports and Switch Downstream Ports.

> +}
> +
> +static void dw_pcie_op_stop_link(struct pci_bus *bus)
> +{
> +	struct dw_pcie_rp *pp = bus->sysdata;
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +
> +	dw_pcie_host_stop_link(pci);
> +}
> +
>  static struct pci_ops dw_pcie_ops = {
>  	.map_bus = dw_pcie_own_conf_map_bus,
>  	.read = pci_generic_config_read,
>  	.write = pci_generic_config_write,
> +	.start_link = dw_pcie_op_start_link,
> +	.stop_link = dw_pcie_op_stop_link,
>  };
>  
>  static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
> 
> -- 
> 2.34.1
>