linux-kernel - Re: [PATCH v6] PCI/ASPM: Update LTR threshold based upon reported max latencies

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Date:   Thu, 25 Aug 2022 01:06:32 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        helgaas@...nel.org, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_vbadigan@...cinc.com, quic_hemantk@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_ramkri@...cinc.com, swboyd@...omium.org,
        dmitry.baryshkov@...aro.org,
        Prasad Malisetty <quic_pmaliset@...cinc.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>
Subject: Re: [PATCH v6] PCI/ASPM: Update LTR threshold based upon reported
 max latencies

On Tue, Jul 26, 2022 at 01:19:54PM +0530, Manivannan Sadhasivam wrote:
> On Fri, Jul 15, 2022 at 05:30:12PM +0530, Krishna chaitanya chundru wrote:
> > In ASPM driver, LTR threshold scale and value are updated based on
> > tcommon_mode and t_poweron values. In kioxia NVMe L1.2 is failing due to
> > LTR threshold scale and value are greater values than max snoop/non-snoop
> > 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.
> > 
> > Signed-off-by: Prasad Malisetty  <quic_pmaliset@...cinc.com>
> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> > Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> 
> Bjorn, any update on this patch?

ping: can this be landed or are any further changes needed?

> Thanks,
> Mani
> 
> > ---
> > 
> > I am taking this patch forward as prasad is no more working with our org.
> > changes since v5:
> > 	- no changes, just reposting as standalone patch instead of reply to
> > 	  previous patch.
> > Changes since v4:
> > 	- Replaced conditional statements with min and max.
> > changes since v3:
> > 	- Changed the logic to include this condition "snoop/nosnoop
> > 	  latencies are not equal to zero and lower than LTR_L1.2_THRESHOLD"
> > 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 | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> > 
> > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > index a96b742..676c03e 100644
> > --- a/drivers/pci/pcie/aspm.c
> > +++ b/drivers/pci/pcie/aspm.c
> > @@ -461,14 +461,36 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
> >  {
> >  	struct pci_dev *child = link->downstream, *parent = link->pdev;
> >  	u32 val1, val2, scale1, scale2;
> > +	u32 max_val, max_scale, max_snp_scale, max_snp_val, max_nsnp_scale, max_nsnp_val;
> >  	u32 t_common_mode, t_power_on, l1_2_threshold, scale, value;
> >  	u32 ctl1 = 0, ctl2 = 0;
> >  	u32 pctl1, pctl2, cctl1, cctl2;
> >  	u32 pl1_2_enables, cl1_2_enables;
> > +	u16 ltr;
> > +	u16 max_snoop_lat, max_nosnoop_lat;
> >  
> >  	if (!(link->aspm_support & ASPM_STATE_L1_2_MASK))
> >  		return;
> >  
> > +	ltr = pci_find_ext_capability(child, PCI_EXT_CAP_ID_LTR);
> > +	if (!ltr)
> > +		return;
> > +
> > +	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);
> > +
> > +	max_snp_scale = (max_snoop_lat & PCI_LTR_SCALE_MASK) >> PCI_LTR_SCALE_SHIFT;
> > +	max_snp_val = max_snoop_lat & PCI_LTR_VALUE_MASK;
> > +
> > +	max_nsnp_scale = (max_nosnoop_lat & PCI_LTR_SCALE_MASK) >> PCI_LTR_SCALE_SHIFT;
> > +	max_nsnp_val = max_nosnoop_lat & PCI_LTR_VALUE_MASK;
> > +
> > +	/* choose the greater max scale value between snoop and no snoop value*/
> > +	max_scale = max(max_snp_scale, max_nsnp_scale);
> > +
> > +	/* choose the greater max value between snoop and no snoop scales */
> > +	max_val = max(max_snp_val, max_nsnp_val);
> > +
> >  	/* 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;
> > @@ -501,6 +523,14 @@ 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);
> > +
> > +	/*
> > +	 * Based on PCIe r4.1, sec 5.5.1, L1.2 substate must be entered when reported
> > +	 * snoop/no-snoop values are greather than or equal to LTR_L1.2_THRESHOLD value.
> > +	 */
> > +	scale = min(scale, max_scale);
> > +	value = min(value, max_val);
> > +
> >  	ctl1 |= t_common_mode << 8 | scale << 29 | value << 16;
> >  
> >  	/* Some broken devices only support dword access to L1 SS */
> > -- 
> > 2.7.4
> >