linux-kernel - Re: [PATCH] PCI: rcar-host: Avoid objtool no-cfi warning in rcar_pcie

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Message-ID: <20251014083209.GA2696801@ax162>
Date: Tue, 14 Oct 2025 01:32:09 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Marek Vasut <marek.vasut+renesas@...il.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Magnus Damm <magnus.damm@...il.com>, linux-pci@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>,
	Kees Cook <kees@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH] PCI: rcar-host: Avoid objtool no-cfi warning in
 rcar_pcie_probe()

Hi Geert,

On Tue, Oct 14, 2025 at 09:16:58AM +0200, Geert Uytterhoeven wrote:
> On Mon, 13 Oct 2025 at 20:26, Nathan Chancellor <nathan@...nel.org> wrote:
> > ---
> > Another alternative is to make this driver depend on CONFIG_OF since it
> > clearly requires it but that would restrict compile testing so I went
> > with this first.
> > ---
> >  drivers/pci/controller/pcie-rcar-host.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
> > index 213028052aa5..15514c9c1927 100644
> > --- a/drivers/pci/controller/pcie-rcar-host.c
> > +++ b/drivers/pci/controller/pcie-rcar-host.c
> > @@ -981,7 +981,7 @@ static int rcar_pcie_probe(struct platform_device *pdev)
> >                 goto err_clk_disable;
> >
> >         host->phy_init_fn = of_device_get_match_data(dev);
> > -       err = host->phy_init_fn(host);
> > +       err = host->phy_init_fn ? host->phy_init_fn(host) : -ENODEV;
> >         if (err) {
> >                 dev_err(dev, "failed to init PCIe PHY\n");
> >                 goto err_clk_disable;
> 
> I am afraid you're playing a big game of whack-a-mole, since we tend
> to remove these checks, as they can never happen in practice (driver
> is probed from DT only, and all entries in rcar_pcie_of_match[] have
> a non-NULL .data member)...

Thanks for the input! Yeah, that is fair, as I alluded to in the scissor
area. We could just do

diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
index 41748d083b93..d8688abc5b27 100644
--- a/drivers/pci/controller/Kconfig
+++ b/drivers/pci/controller/Kconfig
@@ -243,6 +243,7 @@ config PCI_TEGRA
 config PCIE_RCAR_HOST
 	bool "Renesas R-Car PCIe controller (host mode)"
 	depends on ARCH_RENESAS || COMPILE_TEST
+	depends on OF
 	depends on PCI_MSI
 	select IRQ_MSI_LIB
 	help

since it is required for the driver to function. Another alternative
would be something like either:

diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
index 213028052aa5..c237e04392e6 100644
--- a/drivers/pci/controller/pcie-rcar-host.c
+++ b/drivers/pci/controller/pcie-rcar-host.c
@@ -941,6 +941,9 @@ static int rcar_pcie_probe(struct platform_device *pdev)
 	u32 data;
 	int err;
 
+	if (!IS_ENABLED(CONFIG_OF))
+		return -ENODEV;
+
 	bridge = devm_pci_alloc_host_bridge(dev, sizeof(*host));
 	if (!bridge)
 		return -ENOMEM;

or

diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
index 213028052aa5..2aee2e0d9a1d 100644
--- a/drivers/pci/controller/pcie-rcar-host.c
+++ b/drivers/pci/controller/pcie-rcar-host.c
@@ -980,8 +980,12 @@ static int rcar_pcie_probe(struct platform_device *pdev)
 	if (err)
 		goto err_clk_disable;
 
-	host->phy_init_fn = of_device_get_match_data(dev);
-	err = host->phy_init_fn(host);
+	if (IS_ENABLED(CONFIG_OF)) {
+		host->phy_init_fn = of_device_get_match_data(dev);
+		err = host->phy_init_fn(host);
+	} else {
+		err = -ENODEV;
+	}
 	if (err) {
 		dev_err(dev, "failed to init PCIe PHY\n");
 		goto err_clk_disable;

to keep the ability to compile test the driver without CONFIG_OF while
having no impact on the final object code and avoiding the NULL call. I
am open to other thoughts and ideas as well.

Cheers,
Nathan