linux-kernel - Re: [PATCH 03/16] PCI: dwc: Add more verbose link-up message

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Date:   Mon, 28 Mar 2022 16:31:53 -0700
From:   Joe Perches <joe@...ches.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/16] PCI: dwc: Add more verbose link-up message

On Thu, 2022-03-24 at 04:37 +0300, Serge Semin wrote:
> Printing just "link up" isn't that much informative especially when it
> comes to working with the PCI Express bus. Even if the link is up, due to
> multiple reasons the bus performance can degrade to slower speeds or to
> narrower width than both Root Port and its partner is capable of. In that
> case it would be handy to know the link specifications as early as
> possible. So let's add a more verbose message to the busy-wait link-state
> method, which will contain the link speed generation and the PCIe bus
> width in case if the link up state is discovered. Otherwise an error will
> be printed to the system log.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 22 +++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
[]
> @@ -528,14 +528,26 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
>  
>  	/* Check if the link is up or not */
>  	for (retries = 0; retries < LINK_WAIT_MAX_RETRIES; retries++) {
> -		if (dw_pcie_link_up(pci)) {
> -			dev_info(pci->dev, "Link up\n");
> -			return 0;
> -		}
> +		if (dw_pcie_link_up(pci))
> +			break;
> +
>  		usleep_range(LINK_WAIT_USLEEP_MIN, LINK_WAIT_USLEEP_MAX);
>  	}
>  
> -	dev_info(pci->dev, "Phy link never came up\n");
> +	if (retries < LINK_WAIT_MAX_RETRIES) {
> +		u32 offset, val;
> +
> +		offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +		val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
> +
> +		dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
> +			 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
> +			 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
> +
> +		return 0;
> +	}
> +
> +	dev_err(pci->dev, "Phy link never came up\n");
>  
>  	return -ETIMEDOUT;
>  }

IMO: it's generally bette to test the error condition and unindent
the typical return.

	if (retries >= LINK_WAIT_MAX_RETRIES) {
		dev_err(pci->dev, "Phy link never came up\n");
		return -ETIMEDOUT;
	}

	offset = ...
	val = ...
	dev_info(...)

	return 0;
}