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

Krishna chaitanya chundru
2022-09-15T04:32:46Z

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@quicinc.com>
Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.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