[PATCH 1/1] PCI: Reprogram bridge prefetch registers on resume

[Stefan Bader]

On 19.09.2018 17:29, Kai-Heng Feng wrote:
> From: Daniel Drake <drake at endlessm.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1793338
> 
> On 38+ Intel-based ASUS products, the NVIDIA GPU becomes unusable after S3
> suspend/resume.  The affected products include multiple generations of
> NVIDIA GPUs and Intel SoCs.  After resume, nouveau logs many errors such
> as:
> 
>   fifo: fault 00 [READ] at 0000005555555000 engine 00 [GR] client 04
>         [HUB/FE] reason 4a [] on channel -1 [007fa91000 unknown]
>   DRM: failed to idle channel 0 [DRM]
> 
> Similarly, the NVIDIA proprietary driver also fails after resume (black
> screen, 100% CPU usage in Xorg process).  We shipped a sample to NVIDIA for
> diagnosis, and their response indicated that it's a problem with the parent
> PCI bridge (on the Intel SoC), not the GPU.
> 
> Runtime suspend/resume works fine, only S3 suspend is affected.
> 
> We found a workaround: on resume, rewrite the Intel PCI bridge
> 'Prefetchable Base Upper 32 Bits' register (PCI_PREF_BASE_UPPER32).  In the
> cases that I checked, this register has value 0 and we just have to rewrite
> that value.
> 
> Linux already saves and restores PCI config space during suspend/resume,
> but this register was being skipped because upon resume, it already has
> value 0 (the correct, pre-suspend value).
> 
> Intel appear to have previously acknowledged this behaviour and the
> requirement to rewrite this register:
> https://bugzilla.kernel.org/show_bug.cgi?id=116851#c23
> 
> Based on that, rewrite the prefetch register values even when that appears
> unnecessary.
> 
> We have confirmed this solution on all the affected models we have in-hands
> (X542UQ, UX533FD, X530UN, V272UN).
> 
> Additionally, this solves an issue where r8169 MSI-X interrupts were broken
> after S3 suspend/resume on ASUS X441UAR.  This issue was recently worked
> around in commit 7bb05b85bc2d ("r8169: don't use MSI-X on RTL8106e").  It
> also fixes the same issue on RTL6186evl/8111evl on an Aimfor-tech laptop
> that we had not yet patched.  I suspect it will also fix the issue that was
> worked around in commit 7c53a722459c ("r8169: don't use MSI-X on
> RTL8168g").
> 
> Thomas Martitz reports that this change also solves an issue where the AMD
> Radeon Polaris 10 GPU on the HP Zbook 14u G5 is unresponsive after S3
> suspend/resume.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=201069
> Signed-off-by: Daniel Drake <drake at endlessm.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
> Reviewed-By: Peter Wu <peter at lekensteyn.nl>
> (cherry picked from commit 04cb3ae895d7efdc60f0fe17182b200a3da20f09 git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git pci/enumeration)
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> ---
I looks like the change effectively only changes behaviour for bridges, just not
sure whether it is ok to make this change to all bridges. Probably not a real
problem to write a value that is already there but I am not that familiar with
the magics of pci.
So just double checking before acking this.

-Stefan
>  drivers/pci/pci.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index f953042c7cdf..7e600b75d186 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1113,12 +1113,12 @@ int pci_save_state(struct pci_dev *dev)
>  EXPORT_SYMBOL(pci_save_state);
>  
>  static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
> -				     u32 saved_val, int retry)
> +				     u32 saved_val, int retry, bool force)
>  {
>  	u32 val;
>  
>  	pci_read_config_dword(pdev, offset, &val);
> -	if (val == saved_val)
> +	if (!force && val == saved_val)
>  		return;
>  
>  	for (;;) {
> @@ -1137,25 +1137,36 @@ static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
>  }
>  
>  static void pci_restore_config_space_range(struct pci_dev *pdev,
> -					   int start, int end, int retry)
> +					   int start, int end, int retry,
> +					   bool force)
>  {
>  	int index;
>  
>  	for (index = end; index >= start; index--)
>  		pci_restore_config_dword(pdev, 4 * index,
>  					 pdev->saved_config_space[index],
> -					 retry);
> +					 retry, force);
>  }
>  
>  static void pci_restore_config_space(struct pci_dev *pdev)
>  {
>  	if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL) {
> -		pci_restore_config_space_range(pdev, 10, 15, 0);
> +		pci_restore_config_space_range(pdev, 10, 15, 0, false);
>  		/* Restore BARs before the command register. */
> -		pci_restore_config_space_range(pdev, 4, 9, 10);
> -		pci_restore_config_space_range(pdev, 0, 3, 0);
> +		pci_restore_config_space_range(pdev, 4, 9, 10, false);
> +		pci_restore_config_space_range(pdev, 0, 3, 0, false);
> +	} else if (pdev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> +		pci_restore_config_space_range(pdev, 12, 15, 0, false);
> +
> +		/*
> +		 * Force rewriting of prefetch registers to avoid S3 resume
> +		 * issues on Intel PCI bridges that occur when these
> +		 * registers are not explicitly written.
> +		 */
> +		pci_restore_config_space_range(pdev, 9, 11, 0, true);
> +		pci_restore_config_space_range(pdev, 0, 8, 0, false);
>  	} else {
> -		pci_restore_config_space_range(pdev, 0, 15, 0);
> +		pci_restore_config_space_range(pdev, 0, 15, 0, false);
>  	}
>  }
>  
> 


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