Re: [PATCH v3 1/3] PCI: dwc: Skip waiting for link up if vendor drivers can detect Link up event

[Bjorn Andersson]

On Fri, Nov 01, 2024 at 05:04:12PM GMT, Krishna chaitanya chundru wrote:
> If the vendor drivers can detect the Link up event using mechanisms
> such as Link up IRQ and can the driver can enumerate downstream devices
> instead of waiting here, then waiting for Link up during probe is not
> needed here, which optimizes the boot time.
> 
> So skip waiting for link to be up if the driver supports 'linkup_irq'.
> 
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
>  drivers/pci/controller/dwc/pcie-designware.h      |  1 +
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 3e41865c7290..26418873ce14 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -530,8 +530,14 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  			goto err_remove_edma;
>  	}
>  
> -	/* Ignore errors, the link may come up later */
> -	dw_pcie_wait_for_link(pci);
> +	/*
> +	 * Note: The link up delay is skipped only when a link up IRQ is present.
> +	 * This flag should not be used to bypass the link up delay for arbitrary
> +	 * reasons.

Perhaps by improving the naming of the variable, you don't need 3 lines
of comment describing the conditional.

> +	 */
> +	if (!pp->linkup_irq)
> +		/* Ignore errors, the link may come up later */

Does this mean that we will be able to start handling these errors?

> +		dw_pcie_wait_for_link(pci);
>  
>  	bridge->sysdata = pp;
>  
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 347ab74ac35a..539c6d106bb0 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -379,6 +379,7 @@ struct dw_pcie_rp {
>  	bool			use_atu_msg;
>  	int			msg_atu_index;
>  	struct resource		*msg_res;
> +	bool			linkup_irq;

Please name this for what it is, rather than some property from which
some other decision should be derived. (And then you need a comment to
describe how people should interpret and use it)

Also, "linkup_irq" sound like an int carrying the interrupt number, not
a boolean.


Please call it "use_async_linkup", "use_linkup_irq" or something.

Regards,
Bjorn

>  };
>  
>  struct dw_pcie_ep_ops {
> 
> -- 
> 2.34.1
> 
>