linux-kernel - Re: [PATCH v2] [RFC PATCH] PCI: Update LTR threshold based on LTRME bit

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Date:   Thu, 17 Mar 2022 15:07:23 -0400
From:   Stephen Boyd <swboyd@...omium.org>
To:     Prasad Malisetty <quic_pmaliset@...cinc.com>, agross@...nel.org,
        bhelgaas@...gle.com, bjorn.andersson@...aro.org, kw@...ux.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, lorenzo.pieralisi@....com,
        rajatja@...gle.com, refactormyself@...il.com, robh@...nel.org
Cc:     quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
        manivannan.sadhasivam@...aro.org
Subject: Re: [PATCH v2] [RFC PATCH] PCI: Update LTR threshold based on LTRME bit

Quoting Prasad Malisetty (2022-03-07 10:59:09)
> Update LTR threshold scale and value based on LTRME (Latency
> Tolenrance Reporting Mechanism) from device capabilities.
>
> In ASPM driver, LTR threshold scale and value is updating
> based on 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 value.
>
> In general, updated LTR threshold scale and value should be
> less than max snoop/non snoop value to enter the device
> into L1.2 state.
>
> Signed-off-by: Prasad Malisetty <quic_pmaliset@...cinc.com>
>

Any Fixes tag?

> ---
> Changes since v1:
>         - Added missing variable declaration in v1 patch.
> ---
>  drivers/pci/pcie/aspm.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index a96b742..a67746c 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -463,6 +463,7 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
>         u32 val1, val2, scale1, scale2;
>         u32 t_common_mode, t_power_on, l1_2_threshold, scale, value;
>         u32 ctl1 = 0, ctl2 = 0;
> +       u32 cap;
>         u32 pctl1, pctl2, cctl1, cctl2;
>         u32 pl1_2_enables, cl1_2_enables;
>
> @@ -499,9 +500,14 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
>          * Table 5-11.  T(POWER_OFF) is at most 2us and T(L1.2) is at
>          * least 4us.

Can this comment be updated to include why LTR cap matters?

>          */
> -       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;
> +       pcie_capability_read_dword(child, PCI_EXP_DEVCAP2, &cap);
> +       if (!(cap & PCI_EXP_DEVCAP2_LTR)) {
> +               l1_2_threshold = 2 + 4 + t_common_mode + t_power_on;
> +               encode_l12_threshold(l1_2_threshold, &scale, &value);
> +               ctl1 |= scale << 29 | value << 16;
> +       }
> +
> +       ctl1 |= t_common_mode;