Re: [PATCH 1/2] PCI/ASPM: Store disabled ASPM states

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

> On Dec 9, 2020, at 01:11, Heiner Kallweit <hkallweit1@gmail.com> wrote:
> 
> Am 08.12.2020 um 09:25 schrieb Kai-Heng Feng:
>> If we use sysfs to disable L1 ASPM, then enable one L1 ASPM substate
>> again, all other substates will also be enabled too:
>> 
>> link# grep . *
>> clkpm:1
>> l0s_aspm:1
>> l1_1_aspm:1
>> l1_1_pcipm:1
>> l1_2_aspm:1
>> l1_2_pcipm:1
>> l1_aspm:1
>> 
>> link# echo 0 > l1_aspm
>> 
>> link# grep . *
>> clkpm:1
>> l0s_aspm:1
>> l1_1_aspm:0
>> l1_1_pcipm:0
>> l1_2_aspm:0
>> l1_2_pcipm:0
>> l1_aspm:0
>> 
>> link# echo 1 > l1_2_aspm
>> 
>> link# grep . *
>> clkpm:1
>> l0s_aspm:1
>> l1_1_aspm:1
>> l1_1_pcipm:1
>> l1_2_aspm:1
>> l1_2_pcipm:1
>> l1_aspm:1
>> 
>> This is because disabled ASPM states weren't saved, so enable any of the
>> substate will also enable others.
>> 
>> So store the disabled ASPM states for consistency.
>> 
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>> ---
>> drivers/pci/pcie/aspm.c | 10 ++++++++--
>> 1 file changed, 8 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index ac0557a305af..2ea9fddadfad 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -658,6 +658,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>> 	/* Setup initial capable state. Will be updated later */
>> 	link->aspm_capable = link->aspm_support;
>> 
>> +	link->aspm_disable = link->aspm_capable & ~link->aspm_default;
>> +
> 
> This makes sense only in combination with patch 2. However I think patch 1
> should be independent of patch 2. Especially if we consider patch 1 a fix
> that is applied to stable whilst patch 2 is an improvement for next.
> 
>> 	/* Get and check endpoint acceptable latencies */
>> 	list_for_each_entry(child, &linkbus->devices, bus_list) {
>> 		u32 reg32, encoding;
>> @@ -1226,11 +1228,15 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>> 	mutex_lock(&aspm_lock);
>> 
>> 	if (state_enable) {
>> -		link->aspm_disable &= ~state;
>> 		/* need to enable L1 for substates */
>> 		if (state & ASPM_STATE_L1SS)
>> -			link->aspm_disable &= ~ASPM_STATE_L1;
>> +			state |= ASPM_STATE_L1;
>> +
>> +		link->aspm_disable &= ~state;
> 
> I don't see what this part of the patch changes. Can you elaborate on why
> this is needed?

No this is just a cosmetic change. Of course "cosmetic" is really subjective.
I'll drop this part in v2.

> 
>> 	} else {
>> +		if (state == ASPM_STATE_L1)
>> +			state |= ASPM_STATE_L1SS;
>> +
> 
> I think this part should be sufficient to fix the behavior. because what
> I think currently happens:
> 
> 1. original status: policy powersupersave, nothing disabled -> L1 + L1SS active
> 2. disable L1: L1 disabled, pcie_config_aspm_link() disabled L1 and L1SS
>   w/o adding L1SS to link-> aspm_disabled
> 3. enable one L1SS state: aspm_attr_store_common() removes L1 from
>   link->aspm_disabled -> link->aspm_disabled is empty, resulting in
>   L1 + L1SS being active

Yes. This is the case the patch solves.

Kai-Heng

> 
>> 		link->aspm_disable |= state;
>> 	}