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SubjectRe: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated
[+cc Michal, Ley Foon, Jingoo, Thierry, Jonathan]

On Tue, Jun 08, 2021 at 10:04:09AM +0200, Javier Martinez Canillas 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.

I'm not an IRQ expert, but I think this is an issue regardless of
CONFIG_DEBUG_SHIRQ, isn't it? Anything used by an IRQ handler should
be initialized before the handler is registered. CONFIG_DEBUG_SHIRQ
is just a way to help find latent problems.

> 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.

Previously we registered rockchip_pcie_subsys_irq_handler() and
rockchip_pcie_client_irq_handler() before the PCIe clocks were
enabled. That's a problem because they depend on those clocks being
enabled, and your patch fixes that.

rockchip_pcie_legacy_int_handler() depends on rockchip->irq_domain,
which isn't initialized until rockchip_pcie_init_irq_domain().
Previously we registered rockchip_pcie_legacy_int_handler() as the
handler for the "legacy" IRQ before rockchip_pcie_init_irq_domain().

I think you patch *also* fixes that problem, right?

I think this is also an issue with the following other drivers. They all
set the handler to something that uses an IRQ domain before they
actually initialize the domain:

# nwl --------------------------------------------------------------
nwl_pcie_probe
nwl_pcie_parse_dt
pcie->irq_intx = platform_get_irq_byname(pdev, "intx")
irq_set_chained_handler_and_data(pcie->irq_intx, nwl_pcie_leg_handler)
nwl_pcie_bridge_init
devm_request_irq
nwl_pcie_init_irq_domain
pcie->legacy_irq_domain = irq_domain_add_linear()

nwl_pcie_leg_handler
irq_find_mapping(pcie->legacy_irq_domain)


# altera --------------------------------------------------------------
altera_pcie_probe
altera_pcie_parse_dt
irq_set_chained_handler_and_data(altera_pcie_isr)
altera_pcie_init_irq_domain
pcie->irq_domain = irq_domain_add_linear()

altera_pcie_isr
irq_find_mapping(pcie->irq_domain)


# ks --------------------------------------------------------------
ks_pcie_config_legacy_irq
irq_set_chained_handler_and_data(ks_pcie_legacy_irq_handler)
ks_pcie->legacy_irq_domain = irq_domain_add_linear()

ks_pcie_legacy_irq_handler
ks_pcie_handle_legacy_irqirq_linear_revmap(ks_pcie->legacy_irq_domain)


# tegra --------------------------------------------------------------
tegra_pcie_msi_setup
if (IS_ENABLED(CONFIG_PCI_MSI)) {
tegra_allocate_domains
parent = irq_domain_create_linear()
msi->domain = pci_msi_create_irq_domain(parent)
}
irq_set_chained_handler_and_data(tegra_pcie_msi_irq)

tegra_pcie_msi_irq
irq_find_mapping(msi->domain->parent)


Tegra is a little wierd because the IS_ENABLED(CONFIG_PCI_MSI) only
covers the IRQ domain alloc; it doesn't cover setting the handler. So
if CONFIG_PCI_MSI is not set, we don't alloc the IRQ domain, but we
still set a handler that *uses* the IRQ domain. That seems somewhat
broken.

> 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>
> ---
>
> 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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