linux-kernel - Re: [PATCH v4] PCI/ASPM: Update LTR threshold based upon reported max latencies

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Date:   Wed, 8 Jun 2022 15:22:13 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        helgaas@...nel.org
Cc:     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,
        manivannan.sadhasivam@...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 v4] PCI/ASPM: Update LTR threshold based upon reported max latencies

Quoting Krishna chaitanya chundru (2022-06-03 00:54:19)
> From: Prasad Malisetty <quic_pmaliset@...cinc.com>
>
> 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>
> ---
>
> I am taking this patch forward as prasad is no more working with our org.

Not sure why it's a reply to the previous rounds. I didn't notice this
patch for a bit. Can you stop sending as replies to the previous round?

> 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 | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index a96b742..c8f6253 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);

Remove useless parenthesis please.

> +
> +       max_nsnp_scale = (max_nosnoop_lat & PCI_LTR_SCALE_MASK) >> PCI_LTR_SCALE_SHIFT;
> +       max_nsnp_val = (max_nosnoop_lat & PCI_LTR_VALUE_MASK)

Remove useless parenthesis please.

> +
> +       /* choose the greater max scale value between snoop and no snoop value*/
> +       max_scale = (max_snp_scale > max_nsnp_scale) ? max_snp_scale: max_nsnp_scale;

Use max()?

> +
> +       /* choose the greater max value between snoop and no snoop scales */
> +       max_val = (max_snp_val > max_nsnp_val) ? max_snp_val: max_nsnp_val;

Use max()?

> +
>         /* 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 +523,16 @@ 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.
> +        */
> +       if (scale > max_scale)
> +               scale = max_scale;

Use min()?

> +       if (value > max_val)
> +               value = max_val;

Use min()?

> +
>         ctl1 |= t_common_mode << 8 | scale << 29 | value << 16;
>
>         /* Some broken devices only support dword access to L1 SS */