Re: [PATCH] PCI: dwc: rcar-gen4: Fix potential unclocked access in rcar_gen4_pcie_ep_deinit()

[Geert Uytterhoeven]

Hi Den-san,

On Tue, 18 Aug 2026 at 07:55, Koichiro Den <den@xxxxxxxxxxxxx> wrote:
> On Thu, Aug 13, 2026 at 11:18:22AM +0200, Marek Vasut wrote:
> > Initialize PCIEDMAINTSTSEN in rcar_gen4_pcie_ep_pre_init() to 0,
> > and in case rcar_gen4_pcie_common_init() fails and the result
> > propagates to dw_pcie_ep_init(), the invoke common deinit instead
> > of endpoint deinit, because we are certain the PCIEDMAINTSTSEN
> > register is already 0 and the common deinit does not do any register
> > accesses.
> >
> > Signed-off-by: Marek Vasut <marek.vasut+renesas@xxxxxxxxxxx>

> > --- a/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> > +++ b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> > @@ -487,6 +487,8 @@ static int rcar_gen4_pcie_ep_pre_init(struct dw_pcie_ep *ep)
> >       struct rcar_gen4_pcie *rcar = to_rcar_gen4_pcie(dw);
> >       int ret;
> >
> > +     writel(0, rcar->base + PCIEDMAINTSTSEN);
> > +
>
> 1. The new writel(0, PCIEDMAINTSTSEN) runs before clk_bulk_prepare_enable().
>    Is MSTP024 expected to be already released at this point? I added the quick
>    check like below on Spider, and confirmed that the clock was already enabled.
>
>    --- a/drivers/pci/controller/dwc/pcie-rcar-gen4.c
>    +++ b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
>    @@ -9,6 +9,7 @@
>      */
>
>     #include <linux/delay.h>
>    +#include <linux/clk-provider.h>
>     #include <linux/firmware.h>
>     #include <linux/interrupt.h>
>     #include <linux/io.h>
>    @@ -487,6 +488,10 @@ static int rcar_gen4_pcie_ep_pre_init(struct dw_pcie_ep *ep)
>            struct rcar_gen4_pcie *rcar = to_rcar_gen4_pcie(dw);
>            int ret;
>
>    +       if (__clk_is_enabled(dw->core_clks[DW_PCIE_CORE_CLK].clk))
>    +               dev_info(dw->dev,
>    +                        "PCIEC module clock was already enabled\n");
>    +
>            writel(0, rcar->base + PCIEDMAINTSTSEN);
>
>            ret = rcar_gen4_pcie_common_init(rcar);
>
>    If that is not guaranteed, wouldn't this write rely on firmware or some
>    earlier user leaving the module clock enabled?

The module clock is enabled through Runtime PM:

    rcar_gen4_pcie_probe
    -> rcar_gen4_pcie_prepare
            -> pm_runtime_resume_and_get

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds