Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated

[Peter Robinson <pbrobinson@gmail.com>]

On Tue, Jun 8, 2021 at 9:04 AM Javier Martinez Canillas
<javierm@redhat.com> wrote:
>
> IRQ handlers that are registered for shared interrupts can be called at
> any time after have been registered using the request_irq() function.
>
> It's up to drivers to ensure that's always safe for these to be called.
>
> Both the "pcie-sys" and "pcie-client" interrupts are shared, but since
> their handlers are registered very early in the probe function, an error
> later can lead to these handlers being executed before all the required
> resources have been properly setup.
>
> For example, the rockchip_pcie_read() function used by these IRQ handlers
> expects that some PCIe clocks will already be enabled, otherwise trying
> to access the PCIe registers causes the read to hang and never return.
>
> The CONFIG_DEBUG_SHIRQ option tests if drivers are able to cope with their
> shared interrupt handlers being called, by generating a spurious interrupt
> just before a shared interrupt handler is unregistered.
>
> But this means that if the option is enabled, any error in the probe path
> of this driver could lead to one of the IRQ handlers to be executed.
>
> In a rockpro64 board, the following sequence of events happens:
>
>   1) "pcie-sys" IRQ is requested and its handler registered.
>   2) "pcie-client" IRQ is requested and its handler registered.
>   3) probe later fails due readl_poll_timeout() returning a timeout.
>   4) the "pcie-sys" IRQ is unregistered.
>   5) CONFIG_DEBUG_SHIRQ triggers a spurious interrupt.
>   6) "pcie-client" IRQ handler is called for this spurious interrupt.
>   7) IRQ handler tries to read PCIE_CLIENT_INT_STATUS with clocks gated.
>   8) the machine hangs because rockchip_pcie_read() call never returns.
>
> To avoid cases like this, the handlers don't have to be registered until
> very late in the probe function, once all the resources have been setup.
>
> So let's just move all the IRQ init before the pci_host_probe() call, that
> will prevent issues like this and seems to be the correct thing to do too.
>
> Reported-by: Peter Robinson <pbrobinson@gmail.com>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> Acked-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>

Tested on a Rock960, Firefly3399 and a Pinebook Pro

> ---
>
> Changes in v2:
> - Add missing word in the commit message.
> - Include Shawn Lin's Acked-by tag.
>
>  drivers/pci/controller/pcie-rockchip-host.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pci/controller/pcie-rockchip-host.c b/drivers/pci/controller/pcie-rockchip-host.c
> index f1d08a1b159..78d04ac29cd 100644
> --- a/drivers/pci/controller/pcie-rockchip-host.c
> +++ b/drivers/pci/controller/pcie-rockchip-host.c
> @@ -592,10 +592,6 @@ static int rockchip_pcie_parse_host_dt(struct rockchip_pcie *rockchip)
>         if (err)
>                 return err;
>
> -       err = rockchip_pcie_setup_irq(rockchip);
> -       if (err)
> -               return err;
> -
>         rockchip->vpcie12v = devm_regulator_get_optional(dev, "vpcie12v");
>         if (IS_ERR(rockchip->vpcie12v)) {
>                 if (PTR_ERR(rockchip->vpcie12v) != -ENODEV)
> @@ -973,8 +969,6 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
>         if (err)
>                 goto err_vpcie;
>
> -       rockchip_pcie_enable_interrupts(rockchip);
> -
>         err = rockchip_pcie_init_irq_domain(rockchip);
>         if (err < 0)
>                 goto err_deinit_port;
> @@ -992,6 +986,12 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
>         bridge->sysdata = rockchip;
>         bridge->ops = &rockchip_pcie_ops;
>
> +       err = rockchip_pcie_setup_irq(rockchip);
> +       if (err)
> +               goto err_remove_irq_domain;
> +
> +       rockchip_pcie_enable_interrupts(rockchip);
> +
>         err = pci_host_probe(bridge);
>         if (err < 0)
>                 goto err_remove_irq_domain;
> --
> 2.31.1
>

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