linux-kernel - Re: [PATCH v5] PCI/ASPM: Update LTR threshold based upon reported max latencies

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Date:   Fri, 15 Jul 2022 16:58:04 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>, <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>, <swboyd@...omium.org>,
        Prasad Malisetty <quic_pmaliset@...cinc.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Rajat Jain <rajatja@...gle.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        <helgaas@...nel.org>
Subject: Re: [PATCH v5] PCI/ASPM: Update LTR threshold based upon reported max
 latencies


On 7/15/2022 1:58 PM, Manivannan Sadhasivam wrote:
> On Wed, Jun 15, 2022 at 06:53:18PM +0530, Krishna Chaitanya Chundru wrote:
>> A Gentle remainder please review it.
>>
>> On 6/10/2022 10:38 AM, Krishna chaitanya chundru wrote:
>>> 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>
> As Stephen noted in previous verison, you should sent the newer versions
> separately and not as a reply to previous ones. So please sent v6 with
> my tag as well.
>
> Thanks,
> Mani

ok mani I will send the v6 as you suggested.


Thanks

Krishna chaitanya.

>
>>> ---
>>>
>>> I am taking this patch forward as prasad is no more working with our org.
>>> 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 */