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

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Message-ID: <20200925122438.GB3956970@smile.fi.intel.com>
Date:   Fri, 25 Sep 2020 15:24:38 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ethan Zhao <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, 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