Re: [PATCH 1/5] PCI: define a function to check and wait till port finish DPC handling

Andy Shevchenko
2020-09-25T16:40:31Z

On Thu, Sep 24, 2020 at 10:34:19PM -0400, Ethan Zhao wrote:
> Once root port DPC capability is enabled and triggered, at the beginning
> of DPC is triggered, the DPC status bits are set by hardware and then
> sends DPC/DLLSC/PDC interrupts to OS DPC and pciehp drivers, it will
> take the port and software DPC interrupt handler 10ms to 50ms (test data
> on ICX platform & stable 5.9-rc6) to complete the DPC containment procedure
> till the DPC status is cleared at the end of the DPC interrupt handler.
>
> We use this function to check if the root port is in DPC handling status
> and wait till the hardware and software completed the procedure.

> #include <linux/interrupt.h>
> #include <linux/io.h>
> #include <linux/resource_ext.h>

> +#include <linux/delay.h>

Keep it sorted?

> #include <uapi/linux/pci.h>

...

> +#ifdef CONFIG_PCIE_DPC
> +static inline bool pci_wait_port_outdpc(struct pci_dev *pdev)
> +{
> + u16 cap = pdev->dpc_cap, status;
> + u16 loop = 0;
> +
> + if (!cap) {

> + pci_WARN_ONCE(pdev, !cap, "No DPC capability initiated\n");

But why? Is this feature mandatory to have? Then the same question about
ifdeffery, otherwise it's pretty normal to not have a feature, right?

> + return false;
> + }
> + pci_read_config_word(pdev, cap + PCI_EXP_DPC_STATUS, &status);
> + pci_dbg(pdev, "DPC status %x, cap %x\n", status, cap);

> + while (status & PCI_EXP_DPC_STATUS_TRIGGER && loop < 100) {
> + msleep(10);
> + loop++;
> + pci_read_config_word(pdev, cap + PCI_EXP_DPC_STATUS, &status);
> + }

Can we have rather something like readx_poll_timeout() for PCI and use them here?

> + if (!(status & PCI_EXP_DPC_STATUS_TRIGGER)) {
> + pci_dbg(pdev, "Out of DPC status %x, time cost %d ms\n", status, loop*10);
> + return true;
> + }
> + pci_dbg(pdev, "Timeout to wait port out of DPC status\n");
> + return false;
> +}
> +#else
> +static inline bool pci_wait_port_outdpc(struct pci_dev *pdev)
> +{
> + return true;
> +}
> +#endif
> #endif /* LINUX_PCI_H */
> --
> 2.18.4