linux-kernel - Re: [PATCH 3/4 v3] PCI: s32g: Add initial PCIe support (RC)

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Message-ID: <vrgjkulv22hzbx65olh3zpyqxq6dr7d5mepngjwgc3gudjoxwo@ll7xc2teya2s>
Date: Thu, 6 Nov 2025 11:54:18 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>, chester62515@...il.com, 
	mbrugger@...e.com, ghennadi.procopciuc@....nxp.com, s32@....com, 
	bhelgaas@...gle.com, jingoohan1@...il.com, lpieralisi@...nel.org, 
	kwilczynski@...nel.org, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	Ionut.Vicovan@....com, larisa.grigore@....com, Ghennadi.Procopciuc@....com, 
	ciprianmarian.costea@....com, bogdan.hamciuc@....com, Frank.li@....com, 
	linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, imx@...ts.linux.dev, cassel@...nel.org, 
	Richard Zhu <hongxing.zhu@....com>, Lucas Stach <l.stach@...gutronix.de>, 
	Minghuan Lian <minghuan.Lian@....com>, Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>, 
	Christian Bruel <christian.bruel@...s.st.com>, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 3/4 v3] PCI: s32g: Add initial PCIe support (RC)

On Wed, Nov 05, 2025 at 06:05:31PM -0600, Bjorn Helgaas wrote:
> [+cc imx6, layerscape, stm32 maintainers for possible suspend bug]
> 
> On Fri, Oct 24, 2025 at 08:50:46AM +0200, Vincent Guittot wrote:
> > On Wed, 22 Oct 2025 at 21:04, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > On Wed, Oct 22, 2025 at 07:43:08PM +0200, Vincent Guittot wrote:
> > > > Add initial support of the PCIe controller for S32G Soc family. Only
> > > > host mode is supported.
> 
> > > > +static void s32g_init_pcie_controller(struct s32g_pcie *s32g_pp)
> > > > +{
> > > > ...
> > > > +     /*
> > > > +      * Make sure we use the coherency defaults (just in case the settings
> > > > +      * have been changed from their reset values)
> > > > +      */
> > > > +     s32g_pcie_reset_mstr_ace(pci, memblock_start_of_DRAM());
> > >
> > > This seems sketchy and no other driver uses memblock_start_of_DRAM().
> > > Shouldn't a physical memory address like this come from devicetree
> > > somehow?
> > 
> > I was using DT but has been asked to not use it and was proposed to
> > use memblock_start_of_DRAM() instead
> 
> Can you point me to that conversation?
> 
> > > > +     s32g_pp->ctrl_base = devm_platform_ioremap_resource_byname(pdev, "ctrl");
> > > > +     if (IS_ERR(s32g_pp->ctrl_base))
> > > > +             return PTR_ERR(s32g_pp->ctrl_base);
> > >
> > > This looks like the first DWC driver that uses a "ctrl" resource.  Is
> > > this something unique to s32g, or do other drivers have something
> > > similar but use a different name?
> > 
> > AFAICT this seems to be s32g specific in the RM
> 
> It does look like there's very little consistency in reg-names across
> drivers, so I guess it's fine.
> 
> > > > +static int s32g_pcie_suspend_noirq(struct device *dev)
> > > > +{
> > > > +     struct s32g_pcie *s32g_pp = dev_get_drvdata(dev);
> > > > +     struct dw_pcie *pci = &s32g_pp->pci;
> > > > +
> > > > +     if (!dw_pcie_link_up(pci))
> > > > +             return 0;
> > >
> > > Does something bad happen if you omit the link up check and the link
> > > is not up when we get here?  The check is racy (the link could go down
> > > between dw_pcie_link_up() and dw_pcie_suspend_noirq()), so it's not
> > > completely reliable.
> > >
> > > If you have to check, please add a comment about why this driver needs
> > > it when no other driver does.
> > 
> > dw_pcie_suspend_noirq returns an error and the suspend fails
> 
> The implication is that *every* user of dw_pcie_suspend_noirq() would
> have to check for the link being up.  There are only three existing
> callers:
> 
>   imx_pcie_suspend_noirq()
>   ls_pcie_suspend_noirq()
>   stm32_pcie_suspend_noirq()
> 
> but none of them checks for the link being up.
> 

If no devices are attached to the bus, then there is no need to broadcast
PME_Turn_Off and wait for L2/L3. I've just sent out a series that fixes it [1].
Hopefully, this will allow Vincent to use dw_pcie_{suspend/resume}_noirq() APIs.

- Mani

[1] https://lore.kernel.org/linux-pci/20251106061326.8241-1-manivannan.sadhasivam@oss.qualcomm.com/

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