linux-kernel - Re: [PATCH] PCIe ASPM causes machine (HP Compaq 6735s) to sometimes freeze hard at boot at PCI initialization time

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Message-Id: <1228785579.9482.2.camel@sli10-desk.sh.intel.com>
Date:	Tue, 09 Dec 2008 09:19:39 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Thomas Renninger <trenn@...e.de>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	Rafael Wysocki <rwysocki@...e.de>,
	"shemminger@...ux-foundation.org" <shemminger@...ux-foundation.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Stable@...nel.org" <Stable@...nel.org>
Subject: Re: [PATCH] PCIe ASPM causes machine (HP Compaq 6735s) to
	sometimes freeze hard at boot at PCI initialization time

On Mon, 2008-12-08 at 23:17 +0800, Thomas Renninger wrote:
> On Monday 08 December 2008 16:09:19 Matthew Garrett wrote:
> > On Mon, Dec 08, 2008 at 04:04:09PM +0100, Thomas Renninger wrote:
> > > -	pci_read_config_word(pdev, pos + PCI_EXP_LNKCTL, &reg16);
> > > +	parent_reg = pci_read_config_word(pdev, pos + PCI_EXP_LNKCTL, &reg16);
> >
> > I don't think that does what you think it does :)
> 
> Hehe, thanks for the quick and detailed review!
> 
> This one should be better:
> 
> PCIe: ASPM: Break out of endless loop waiting for PCI config bits to switch
> 
> Makes a Compaq 6735s boot reliably again which hang in the loop
> on some boots.
> 
> Signed-off-by: Thomas Renninger <trenn@...e.de>
> 
> ---
>  drivers/pci/pcie/aspm.c |   28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.27/drivers/pci/pcie/aspm.c
> ===================================================================
> --- linux-2.6.27.orig/drivers/pci/pcie/aspm.c
> +++ linux-2.6.27/drivers/pci/pcie/aspm.c
> @@ -16,6 +16,7 @@
>  #include <linux/pm.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> +#include <linux/jiffies.h>
>  #include <linux/pci-aspm.h>
>  #include "../pci.h"
>  
> @@ -161,11 +162,12 @@ static void pcie_check_clock_pm(struct p
>   */
>  static void pcie_aspm_configure_common_clock(struct pci_dev *pdev)
>  {
> -	int pos, child_pos;
> +	int pos, child_pos, i = 0;
>  	u16 reg16 = 0;
>  	struct pci_dev *child_dev;
>  	int same_clock = 1;
> -
> +	unsigned long start_jiffies = jiffies;
> +	u16 child_regs[256], parent_reg;
child_regs[8] should be enough. There should be just one pcie slot under
the port.

>  	/*
>  	 * all functions of a slot should have the same Slot Clock
>  	 * Configuration, so just check one function
> @@ -191,16 +193,19 @@ static void pcie_aspm_configure_common_c
>  		child_pos = pci_find_capability(child_dev, PCI_CAP_ID_EXP);
>  		pci_read_config_word(child_dev, child_pos + PCI_EXP_LNKCTL,
>  			&reg16);
> +		child_regs[i] = reg16;
>  		if (same_clock)
>  			reg16 |= PCI_EXP_LNKCTL_CCC;
>  		else
>  			reg16 &= ~PCI_EXP_LNKCTL_CCC;
>  		pci_write_config_word(child_dev, child_pos + PCI_EXP_LNKCTL,
>  			reg16);
> +		i++;
>  	}
>  
>  	/* Configure upstream component */
>  	pci_read_config_word(pdev, pos + PCI_EXP_LNKCTL, &reg16);
> +	parent_reg = reg16;
>  	if (same_clock)
>  		reg16 |= PCI_EXP_LNKCTL_CCC;
>  	else
> @@ -212,12 +217,29 @@ static void pcie_aspm_configure_common_c
>  	pci_write_config_word(pdev, pos + PCI_EXP_LNKCTL, reg16);
>  
>  	/* Wait for link training end */
> -	while (1) {
> +	/* break out after waiting for 1 second */
should we set start_jiffies here? Otherwise, it's ok to me.

Thanks,
Shaohua

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