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

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Message-ID: <YyNL4lwmh0mz5CcV@google.com>
Date:   Thu, 15 Sep 2022 15:59:30 +0000
From:   Matthias Kaehlcke <mka@...omium.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_hemantk@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_ramkri@...cinc.com, manivannan.sadhasivam@...aro.org,
        swboyd@...omium.org, dmitry.baryshkov@...aro.org,
        Prasad Malisetty <quic_pmaliset@...cinc.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Rajat Jain <rajatja@...gle.com>,
        Krzysztof Wilczyński <kw@...ux.com>
Subject: Re: [RESEND PATCH v6] PCI/ASPM: Update LTR threshold based upon
 reported max latencies

Hi Krishna,

Your patch doesn't apply on pci/next due to changes to aspm_calc_l1ss_info()
from commit 1d46154eed48 ("PCI/ASPM: Refactor L1 PM Substates Control
Register programming"). Please send a rebased version.

Thanks

Matthias

On Thu, Sep 15, 2022 at 10:02:06AM +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>
> ---
> 
> 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
>