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

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Message-ID: <b5675a83-c12c-1f10-2ca2-66e4ee672fe6@quicinc.com>
Date:   Mon, 29 Aug 2022 13:44:22 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Bjorn Helgaas <bhelgaas@...gle.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>, <swboyd@...omium.org>,
        <dmitry.baryshkov@...aro.org>,
        Prasad Malisetty <quic_pmaliset@...cinc.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v6] PCI/ASPM: Update LTR threshold based upon reported max
 latencies


On 8/25/2022 1:36 PM, Matthias Kaehlcke wrote:
> On Tue, Jul 26, 2022 at 01:19:54PM +0530, Manivannan Sadhasivam wrote:
>> On Fri, Jul 15, 2022 at 05:30:12PM +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>
>> Bjorn, any update on this patch?
> ping: can this be landed or are any further changes needed?

Hi Bjorn,

Can you help us to review this patch. It was untouched from july 15. If 
you have

any comments we will try to address them.


Thanks & Regards,

Krishna Chaitanya.

>> Thanks,
>> Mani
>>
>>> ---
>>>
>>> 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
>>>