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

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Date:   Thu, 2 Jun 2022 13:59:38 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc:     helgaas@...nel.org, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
        swboyd@...omium.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>, vidyas@...dia.com,
        kenny@...ix.com
Subject: Re: [PATCH v3] PCI/ASPM: Update LTR threshold based upon reported
 max latencies

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@...cinc.com>
> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>

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.

> > ---
> > 
> > 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.

> > +	u16 max_snoop_lat = 0, max_nosnoop_lat = 0;

No need to initialize these variables.

> >   	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?

> > +
> > +	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

> > +	 */
> > +	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);

-- 
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