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

Zhao, Haifeng
2020-09-27T01:53:44Z

Andy,
About the header file, yes, to keep the order.
The function was already defined with #ifdef CONFIG_PCIE_DPC.
As to ' readx_poll_timeout()' if there is generic one, I would like to use it.
Seems there is no yet ?

Thanks,
Ethan

-----Original Message-----
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Sent: Friday, September 25, 2020 8:25 PM
To: Zhao, Haifeng <haifeng.zhao@intel.com>
Cc: bhelgaas@google.com; oohall@gmail.com; ruscur@russell.cc; lukas@wunner.de; stuart.w.hayes@gmail.com; mr.nuke.me@gmail.com; mika.westerberg@linux.intel.com; linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org; Jia, Pei P <pei.p.jia@intel.com>
Subject: Re: [PATCH 1/5] PCI: define a function to check and wait till port finish DPC handling

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