linux-kernel - Re: [PATCH v2 3/3] PCI/AER: Provide reset

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Date:	Tue, 4 Jun 2013 04:36:44 -0400
From:	Chen Gong <gong.chen@...ux.intel.com>
To:	Betty Dall <betty.dall@...com>
Cc:	rjw@...k.pl, bhelgaas@...gle.com, ying.huang@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 3/3] PCI/AER: Provide reset_link for firmware first
 root port

On Thu, May 30, 2013 at 08:39:29AM -0600, Betty Dall wrote:
> Date:	Thu, 30 May 2013 08:39:29 -0600
> From: Betty Dall <betty.dall@...com>
> To: rjw@...k.pl, bhelgaas@...gle.com
> Cc: ying.huang@...el.com, linux-acpi@...r.kernel.org,
>  linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, Betty Dall
>  <betty.dall@...com>
> Subject: [PATCH v2 3/3] PCI/AER: Provide reset_link for firmware first root
>  port
> X-Mailer: git-send-email 1.7.7.6
> 
> The firmware first path does not install the aerdrv root port
> service driver, so the firmware first root port does not have
> a reset_link callback. When a firmware first root port does not have
> a reset_link callback, use a new default reset_link similar to what
> we already do for the default_downstream_reset_link(). The firmware
> first default reset_link brings the root port out of SBR if firmware
> left it in SBR.
> 
> Changes since v1:
> Removed incorrect setting of p2p_ctrl after the read.
> 
> Signed-off-by: Betty Dall <betty.dall@...com>
> ---
> 
>  drivers/pci/pcie/aer/aerdrv_core.c |   36 ++++++++++++++++++++++++++++++++++++
>  1 files changed, 36 insertions(+), 0 deletions(-)
> 
> 
> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
> index 8ec8b4f..72f76cd 100644
> --- a/drivers/pci/pcie/aer/aerdrv_core.c
> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> @@ -413,6 +413,39 @@ static pci_ers_result_t default_downstream_reset_link(struct pci_dev *dev)
>  	return PCI_ERS_RESULT_RECOVERED;
>  }
>  
> +/**
> + * default_ff_root_port_reset_link - default reset function for firmware
> + *		first Root Port
> + * @dev: pointer to root port's pci_dev data structure
> + *
> + * Invoked when performing link reset at Root Port w/ no aer driver.
> + * This happens through the firmware first path. Firmware may leave
> + * the Root Port in SBR and it is the OS responsiblity to bring it out
> + * of SBR.
> + */
> +static pci_ers_result_t default_ff_root_port_reset_link(struct pci_dev *dev)
> +{
> +	u16 p2p_ctrl;
> +
> +	/* Read Secondary Bus Reset */
> +	pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &p2p_ctrl);
> +
> +	/* De-assert Secondary Bus Reset, if it is set */
> +	if (p2p_ctrl & PCI_BRIDGE_CTL_BUS_RESET) {
> +		p2p_ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
> +		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, p2p_ctrl);
> +
> +		/*
> +		 * System software must wait for at least 100ms from the end
> +		 * of a reset of one or more device before it is permitted
> +		 * to issue Configuration Requests to those devices.
> +		 */
> +		msleep(200);
> +		dev_dbg(&dev->dev, "Root Port link has been reset\n");
> +	}
> +	return PCI_ERS_RESULT_RECOVERED;
> +}

I don't think this function is OK.
1) You don't really reset the 2nd Bus but just checking its status.
I think you should have following steps to reset 2nd Bus:

a. Assert 2nd Bus Reset
b. wait for some time until this message has been broadcasted well
c. De-assert 2nd Bus Reset
d. wait for Trst time

IOW, since we have aer_do_secondary_bus_reset to perform secondary bus
reset, why you repeat it again?

2) msleep(200) is too long for kernel. You'd better yield the CPU when
sleep.

> +
>  static int find_aer_service_iter(struct device *device, void *data)
>  {
>  	struct pcie_port_service_driver *service_driver, **drv;
> @@ -460,6 +493,9 @@ static pci_ers_result_t reset_link(struct pci_dev *dev)
>  		status = driver->reset_link(udev);
>  	} else if (pci_pcie_type(udev) == PCI_EXP_TYPE_DOWNSTREAM) {
>  		status = default_downstream_reset_link(udev);
> +	} else if (pci_pcie_type(udev) == PCI_EXP_TYPE_ROOT_PORT &&
> +		pcie_aer_get_firmware_first(udev)) {
> +		status = default_ff_root_port_reset_link(udev);
>  	} else {
>  		dev_printk(KERN_DEBUG, &dev->dev,
>  			"no link-reset support at upstream device %s\n",
> --
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