Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <20f88022-e9b1-53b3-8832-85edc713ef6a@quicinc.com>
Date:   Wed, 15 Jun 2022 18:53:18 +0530
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Subject: Re: [PATCH v5] PCI/ASPM: Update LTR threshold based upon reported max
 latencies
Content-Language: en-US
To:     Bjorn Helgaas <bhelgaas@google.com>
CC:     <linux-pci@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <quic_vbadigan@quicinc.com>,
        <quic_hemantk@quicinc.com>, <quic_nitegupt@quicinc.com>,
        <quic_skananth@quicinc.com>, <quic_ramkri@quicinc.com>,
        <manivannan.sadhasivam@linaro.org>, <swboyd@chromium.org>,
        Prasad Malisetty <quic_pmaliset@quicinc.com>,
        "Saheed O. Bolarinwa" <refactormyself@gmail.com>,
        Rajat Jain <rajatja@google.com>,
        =?UTF-8?Q?Krzysztof_Wilczy=c5=84ski?= <kw@linux.com>,
        <helgaas@kernel.org>
References: <1654242861-15695-1-git-send-email-quic_krichai@quicinc.com>
 <1654837710-30561-1-git-send-email-quic_krichai@quicinc.com>
From:   Krishna Chaitanya Chundru <quic_krichai@quicinc.com>
In-Reply-To: <1654837710-30561-1-git-send-email-quic_krichai@quicinc.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

A Gentle remainder please review it.

On 6/10/2022 10:38 AM, Krishna chaitanya chundru wrote:
> From: Prasad Malisetty <quic_pmaliset@quicinc.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@quicinc.com>
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
> ---
>
> 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 */