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

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Message-ID: <20220416080109.pqnuojor6lewltr3@mobilestation>
Date:   Sat, 16 Apr 2022 11:01:09 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     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>,
        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 Mon, Mar 28, 2022 at 04:31:53PM -0700, Joe Perches wrote:
> 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.

Absolutely right. Thanks for noticing that. No idea why I haven't done
the way you said 'cause it seems neater, more maintainable than what I
suggested here.

-Sergey

> 
> 	if (retries >= LINK_WAIT_MAX_RETRIES) {
> 		dev_err(pci->dev, "Phy link never came up\n");
> 		return -ETIMEDOUT;
> 	}
> 
> 	offset = ...
> 	val = ...
> 	dev_info(...)
> 
> 	return 0;
> }
>