Re: [PATCH 1/3] PCI/PM: Observe reset delay irrespective of bridge_d3

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 12/31/22 10:33 AM, Lukas Wunner wrote:
> If a PCI bridge is suspended to D3cold upon entering system sleep,
> resuming it entails a Fundamental Reset per PCIe r6.0 sec 5.8.
> 
> The delay prescribed after a Fundamental Reset in PCIe r6.0 sec 6.6.1
> is sought to be observed by:
> 
>   pci_pm_resume_noirq()
>     pci_pm_bridge_power_up_actions()
>       pci_bridge_wait_for_secondary_bus()
> 
> However, pci_bridge_wait_for_secondary_bus() bails out if the bridge_d3
> flag is not set.  That flag indicates whether a bridge is allowed to
> suspend to D3cold at *runtime*.
> 
> Hence *no* delay is observed on resume from system sleep if runtime
> D3cold is forbidden.  That doesn't make any sense, so drop the bridge_d3
> check from pci_bridge_wait_for_secondary_bus().
> 
> The purpose of the bridge_d3 check was probably to avoid delays if a
> bridge remained in D0 during suspend.  However the sole caller of
> pci_bridge_wait_for_secondary_bus(), pci_pm_bridge_power_up_actions(),
> is only invoked if the previous power state was D3cold.  Hence the
> additional bridge_d3 check seems superfluous.
> 
> Fixes: ad9001f2f411 ("PCI/PM: Add missing link delays required by the PCIe spec")
> Tested-by: Ravi Kishore Koppuravuri <ravi.kishore.koppuravuri@intel.com>
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Cc: stable@vger.kernel.org # v5.5+
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index fba95486caaf..f43f3e84f634 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4964,7 +4964,7 @@ void pci_bridge_wait_for_secondary_bus(struct pci_dev *dev)
>  	if (pci_dev_is_disconnected(dev))
>  		return;
>  
> -	if (!pci_is_bridge(dev) || !dev->bridge_d3)
> +	if (!pci_is_bridge(dev))
>  		return;
>  
>  	down_read(&pci_bus_sem);

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer