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

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Date:   Sun, 27 Sep 2020 01:53:34 +0000
From:   "Zhao, Haifeng" <haifeng.zhao@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "oohall@...il.com" <oohall@...il.com>,
        "ruscur@...sell.cc" <ruscur@...sell.cc>,
        "lukas@...ner.de" <lukas@...ner.de>,
        "stuart.w.hayes@...il.com" <stuart.w.hayes@...il.com>,
        "mr.nuke.me@...il.com" <mr.nuke.me@...il.com>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jia, Pei P" <pei.p.jia@...el.com>
Subject: RE: [PATCH 1/5] PCI: define a function to check and wait till port
 finish DPC handling

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@...ux.intel.com> 
Sent: Friday, September 25, 2020 8:25 PM
To: Zhao, Haifeng <haifeng.zhao@...el.com>
Cc: bhelgaas@...gle.com; oohall@...il.com; ruscur@...sell.cc; lukas@...ner.de; stuart.w.hayes@...il.com; mr.nuke.me@...il.com; mika.westerberg@...ux.intel.com; linux-pci@...r.kernel.org; linux-kernel@...r.kernel.org; Jia, Pei P <pei.p.jia@...el.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
> 

-- 
With Best Regards,
Andy Shevchenko