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

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Date:   Fri,  3 Jun 2022 13:24:19 +0530
From:   Krishna chaitanya chundru <quic_krichai@...cinc.com>
To:     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, swboyd@...omium.org,
        Prasad Malisetty <quic_pmaliset@...cinc.com>,
        Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>
Subject: [PATCH v4] PCI/ASPM: Update LTR threshold based upon reported max latencies

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.
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);
+
+	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_snp_scale > max_nsnp_scale) ? max_snp_scale: max_nsnp_scale;
+
+	/* 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;
+
 	/* 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;
+	if (value > max_val)
+		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