linux-kernel - Re: [PATCH 2/2] PCI: dwc: Add multi-port controller support

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Message-ID: <aV17yIhuOFLGYi8r@fedora>
Date: Tue, 6 Jan 2026 22:16:56 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Sumit Kumar <sumit.kumar@....qualcomm.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, Yue Wang <yue.wang@...ogic.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Kevin Hilman <khilman@...libre.com>,
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	Chuanhua Lei <lchuanhua@...linear.com>,
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	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
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	Magnus Damm <magnus.damm@...il.com>,
	Pratyush Anand <pratyush.anand@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, imx@...ts.linux.dev,
	linux-amlogic@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
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	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 2/2] PCI: dwc: Add multi-port controller support

On Tue, Jan 06, 2026 at 06:41:09PM +0530, Manivannan Sadhasivam wrote:
> > One advantage I can see, instead of doing:
> > 
> > +	struct dw_pcie_port *port = list_first_entry(&pci->pp.ports,
> > +						struct dw_pcie_port, list);
> > +	return dw_pcie_wait_for_link(pci, port);
> > 
> > for drivers with only one port (most drivers), we could just instead do:
> > 
> > +	return dw_pcie_wait_for_link(pci, pci->pp.port);
> > 
> > To simply get the first element in the array. No need to sprinkle
> > list_first_entry() everywhere in all the drivers if they just have one port.
> > 
> > 
> > For iterating, to avoid manually traversing the array, we could do like
> > libata and create a simple macro, e.g. ata_qc_for_each():
> > https://github.com/torvalds/linux/blob/v6.19-rc4/drivers/ata/libata-eh.c#L851-L854
> > https://github.com/torvalds/linux/blob/v6.19-rc4/include/linux/libata.h#L1657-L1659
> > 
> 
> I specifically do not want to introduce custom helpers. That's one of my primary
> motivation for using lists :)

You are the maintainer.

IMO it would still be nice if we could avoid sprinkling:

+struct dw_pcie_port *port = list_first_entry(&pci->pp.ports,
+                                             struct dw_pcie_port, list);

all over the glue drivers somehow, especially those that will only have a
single port. Perhaps by introducing a macro?

In case you don't like the idea of introducing a macro to get the first
port...
Since most glue drivers only seem to use the port when calling
dw_pcie_wait_for_link(), perhaps we could introduce an alternate version
of dw_pcie_wait_for_link(), that can be called by glue drivers that only
have a single port.


Kind regards,
Niklas