Re: [PATCH v3] PCI/ASPM: Update LTR threshold based upon reported max latencies

[Krishna Chaitanya Chundru]

On 6/2/2022 1:59 PM, Manivannan Sadhasivam wrote:
> On Wed, Jun 01, 2022 at 05:57:53PM +0530, Krishna Chaitanya Chundru wrote:
> > [+cc kenny, vidya]
> >
> > On 6/1/2022 5:53 PM, Krishna chaitanya chundru wrote:
> > > In ASPM driver, LTR threshold scale and value is updating based on
> s/is/are
>
> s/updating/updated
>
> > > tcommon_mode and t_poweron values. In kioxia NVMe L1.2 is failing due to
> > > LTR threshold scale and value is greater values than max snoop/non-snoop
> s/is/are
>
> > > value.
> > >
> > > Based on PCIe r4.1, sec 5.5.1, L1.2 substate must be entered when
> > > reported snoop/no-snoop values is greather than or equal to
> > > LTR_L1.2_THRESHOLD value.
> > >
> > > Suggested-by: Prasad Malisetty  <quic_pmaliset@xxxxxxxxxxx>
> > > Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
> If you are inheriting the patch from Prasad, then you should still give the
> authorship to him (unless the patch has changed significantly). You can add
> your S-o-b tag to convey that you are carrying the patch from him.
Thanks mani for pointing this, I will modify this in next patch.
> > > ---
> > >
> > > I am takking this patch forward as prasad is no more working with our org.
> > >
> > > Changes since v2:
> > > 	- Replaced LTRME logic with max snoop/no-snoop latencies check.
> > > Changes since v1:
> > > 	- Added missing variable declaration in v1 patch
> > > ---
> > >    drivers/pci/pcie/aspm.c | 22 +++++++++++++++++++++-
> > >    1 file changed, 21 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > > index a96b742..4a15e50 100644
> > > --- a/drivers/pci/pcie/aspm.c
> > > +++ b/drivers/pci/pcie/aspm.c
> > > @@ -465,10 +465,19 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
> > >    	u32 ctl1 = 0, ctl2 = 0;
> > >    	u32 pctl1, pctl2, cctl1, cctl2;
> > >    	u32 pl1_2_enables, cl1_2_enables;
> > > +	int ltr;
> This could be u16 too.
Will change in the next patch
> > > +	u16 max_snoop_lat = 0, max_nosnoop_lat = 0;
> No need to initialize these variables.
I will update these in next patch.
> > >    	if (!(link->aspm_support & ASPM_STATE_L1_2_MASK))
> > >    		return;
> > > +	ltr = pci_find_ext_capability(child, PCI_EXT_CAP_ID_LTR);
> > > +	if (!ltr)
> > > +		return;
> Is this capability implemented always?

Based up on spec 4.1, sec 5.5 Ports that support the L1.2 substate for 
ASPM L1 must support this.

And there is already a check in this function  if there is no L1.2 
support the function is returning.

> > > +
> > > +	pci_read_config_word(child, ltr + PCI_LTR_MAX_SNOOP_LAT, &max_snoop_lat);
> > > +	pci_read_config_word(child, ltr + PCI_LTR_MAX_NOSNOOP_LAT, &max_nosnoop_lat);
> > > +
> > >    	/* Choose the greater of the two Port Common_Mode_Restore_Times */
> > >    	val1 = (parent_l1ss_cap & PCI_L1SS_CAP_CM_RESTORE_TIME) >> 8;
> > >    	val2 = (child_l1ss_cap & PCI_L1SS_CAP_CM_RESTORE_TIME) >> 8;
> > > @@ -501,7 +510,18 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
> > >    	 */
> > >    	l1_2_threshold = 2 + 4 + t_common_mode + t_power_on;
> > >    	encode_l12_threshold(l1_2_threshold, &scale, &value);
> > > -	ctl1 |= t_common_mode << 8 | scale << 29 | value << 16;
> > > +
> > > +	/*
> > > +	 * If the max snoop and no snoop latencies are '0', then avoid updating scale
> > > +	 * and value.
> > > +	 *
> This looks fine but...
>
> > > +	 * Based on PCIe r4.1, sec 5.5.1, L1.2 substate must be entered when reported
> > > +	 * snoop/no-snoop values is greather than or equal to LTR_L1.2_THRESHOLD value.
> s/is/are
>
> What about this? What if the snoop/nosnoop latencies are not equal to zero and
> lower than LTR_L1.2_THRESHOLD?
>
> Thanks,
> Mani

Will address this in next patch.

Thanks,

Krishna Chaitanya.

> > > +	 */
> > > +	if ((max_snoop_lat == 0) && (max_nosnoop_lat == 0))
> > > +		ctl1 |= t_common_mode << 8;
> > > +	else
> > > +		ctl1 |= t_common_mode << 8 | scale << 29 | value << 16;
> > >    	/* Some broken devices only support dword access to L1 SS */
> > >    	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1, &pctl1);