linux-kernel - Re: [PATCH 1/2] PCI: dwc-host: Add a warning to prevent invalid values

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Date:   Thu, 10 Nov 2022 15:32:39 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     JunDong Song <jundongsong1@...il.com>
Cc:     jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] PCI: dwc-host: Add a warning to prevent invalid
 values

The subject lines are not quite accurate.  The warning does nothing to
*prevent* invalid values; it only warns about them.

And it should say what *kind* of values we're talking about.

Maybe:

  PCI: dwc: Warn about invalid 'max-link-speed' from DT

On Mon, Nov 07, 2022 at 11:31:07PM +0800, JunDong Song wrote:
> of_pci_get_max_link_speed() may return a negative value,
> causing the controller to not set the speed correctly.
> Add a warning in case the driver engineer misses it.

Rewrap this to fill 75 columns.

I would probably squash these into a single patch since they're
doing exactly the same thing to the host and endpoint cases.

> Signed-off-by: JunDong Song <jundongsong1@...il.com>
> ---
> 
> When I use the pcie dwc driver, the controller speed is abnormal,
> but it has not been detected because of the @max-link-speed error,
> so I think I need to return an error or warning here.
> 
> Thanks.
> 
>  drivers/pci/controller/dwc/pcie-designware-ep.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 83ddb1902..573342601 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -739,8 +739,11 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
>  		return -ENOMEM;
>  	ep->outbound_addr = addr;
>  
> -	if (pci->link_gen < 1)
> +	if (pci->link_gen < 1) {
>  		pci->link_gen = of_pci_get_max_link_speed(np);
> +		if (unlikely(pci->link_gen < 0))

Using "unlikely" here is unnecessary since this is not a performance
path, and it's a distraction.

> +			dev_warn(dev, "Failed to get max link speed\n");
> +	}
>  
>  	epc = devm_pci_epc_create(dev, &epc_ops);
>  	if (IS_ERR(epc)) {
> -- 
> 2.25.1
>