linux-kernel - Re: [PATCH v2] PCI: dwc: Add support to add GEN3 related equalization quirks

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Message-ID: <b81c8f18-7066-2a03-fe52-fb8d41e35fea@nvidia.com>
Date:   Wed, 25 Sep 2019 09:41:11 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Pankaj Dubey <pankaj.dubey@...sung.com>,
        'Gustavo Pimentel' <Gustavo.Pimentel@...opsys.com>,
        'Andrew Murray' <andrew.murray@....com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jingoohan1@...il.com>, <lorenzo.pieralisi@....com>,
        <bhelgaas@...gle.com>, 'Anvesh Salveru' <anvesh.s@...sung.com>
Subject: Re: [PATCH v2] PCI: dwc: Add support to add GEN3 related equalization
 quirks

On 9/24/2019 5:41 PM, Pankaj Dubey wrote:
> 
> 
>> -----Original Message-----
>> From: Vidya Sagar <vidyas@...dia.com>
>> Sent: Tuesday, September 24, 2019 4:57 PM
>> To: Pankaj Dubey <pankaj.dubey@...sung.com>; 'Gustavo Pimentel'
>> <Gustavo.Pimentel@...opsys.com>; 'Andrew Murray'
>> <andrew.murray@....com>
>> Cc: linux-pci@...r.kernel.org; linux-kernel@...r.kernel.org;
>> jingoohan1@...il.com; lorenzo.pieralisi@....com; bhelgaas@...gle.com;
>> 'Anvesh Salveru' <anvesh.s@...sung.com>
>> Subject: Re: [PATCH v2] PCI: dwc: Add support to add GEN3 related equalization
>> quirks
>>
>> On 9/24/2019 2:58 PM, Pankaj Dubey wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Vidya Sagar <vidyas@...dia.com>
>>>> Sent: Thursday, September 19, 2019 4:54 PM
>>>> Subject: Re: [PATCH v2] PCI: dwc: Add support to add GEN3 related
>>>> equalization quirks
>>>>
>>>> On 9/16/2019 6:22 PM, Gustavo Pimentel wrote:
>>>>> On Mon, Sep 16, 2019 at 13:24:1, Andrew Murray
>>>> <andrew.murray@....com>
>>>>> wrote:
>>>>>
>>>>>> On Mon, Sep 16, 2019 at 04:36:33PM +0530, Pankaj Dubey wrote:
>>>>>>>
>>>>>>>
>>>>>>>> -----Original Message-----
>>>>>>>> From: Andrew Murray <andrew.murray@....com>
>>>>>>>> Sent: Monday, September 16, 2019 3:46 PM
>>>>>>>> To: Pankaj Dubey <pankaj.dubey@...sung.com>
>>>>>>>> Cc: linux-pci@...r.kernel.org; linux-kernel@...r.kernel.org;
>>>>>>>> jingoohan1@...il.com; gustavo.pimentel@...opsys.com;
>>>>>>>> lorenzo.pieralisi@....com; bhelgaas@...gle.com; Anvesh Salveru
>>>>>>>> <anvesh.s@...sung.com>
>>>>>>>> Subject: Re: [PATCH v2] PCI: dwc: Add support to add GEN3 related
>>>>>>> equalization
>>>>>>>> quirks
>>>>>>>>
>>>>>>>> On Fri, Sep 13, 2019 at 04:09:50PM +0530, Pankaj Dubey wrote:
>>>>>>>>> From: Anvesh Salveru <anvesh.s@...sung.com>
>>>>>>>>>
>>>>>>>>> In some platforms, PCIe PHY may have issues which will prevent
>>>>>>>>> linkup to happen in GEN3 or higher speed. In case equalization
>>>>>>>>> fails, link will fallback to GEN1.
>>>>>>>>>
>>>>>>>>> DesignWare controller gives flexibility to disable GEN3
>>>>>>>>> equalization completely or only phase 2 and 3 of equalization.
>>>>>>>>>
>>>>>>>>> This patch enables the DesignWare driver to disable the PCIe
>>>>>>>>> GEN3 equalization by enabling one of the following quirks:
>>>>>>>>>     - DWC_EQUALIZATION_DISABLE: To disable GEN3 equalization all
>>>>>>>>> phases
>>>> I don't think Gen-3 equalization can be skipped altogether.
>>>> PCIe Spec Rev 4.0 Ver 1.0 in Section-4.2.3 has the following statement.
>>>>
>>>> "All the Lanes that are associated with the LTSSM (i.e., those Lanes
>>>> that are currently operational or may be operational in the future
>>>> due to Link
>>>> Upconfigure) must participate in the Equalization procedure"
>>>>
>>>> and in Section-4.2.6.4.2.1.1 it says
>>>> "Note: A transition to Recovery.RcvrLock might be used in the case
>>>> where the Downstream Port determines that Phase 2 and Phase 3 are not
>>>> needed based on the platform and channel characteristics."
>>>>
>>>> Based on the above statements, I think it is Ok to skip only Phases
>>>> 2&3 of equalization but not 0&1.
>>>> I even checked with our hardware engineers and it seems
>>>> DWC_EQUALIZATION_DISABLE is present only for debugging purpose in
>>>> hardware simulations and shouldn't be used on real silicon otherwise it seems.
>>>>
>>>
>>> In DesignWare manual we don't see any comment that this feature is for
>> debugging purpose only.
>> Agree and as I mentioned even I got to know about it offline.
>>
>>> Even if it is meant for debugging purpose, if for some reason in an SoC, Gen3/4
>> linkup is failing due to equalization, and if disabling equalization is helping then
>> IMO it is OK to do it.
>> Well, I don't have specific reservations to not have it. We can use this as a fall
>> back option.
>>
>>> Just to re-confirm we tested one of the NVMe device on Jatson AGX Xavier RC
>> with equalization disabled. We do see linkup works well in GEN3. As we have
>> added this feature as a platform-quirk so only platforms that required this
>> feature can enable it.
>>>
>> Curious to know...You did it because link didn't come up with equalization
>> enabled? or just as an experiment?
>>
> 
> We did this, just as an experiment.
Ok. Thanks for the clarification.

Reviewed-by: Vidya Sagar <vidyas@...dia.com>

> 
>>> Snippet of lspci (from Jatson AGX Xavier RC) is given below, showing
>>> EQ is completely disabled and GEN3 linkup
>>> -----
>>> 0005:01:00.0 Non-Volatile memory controller: Lite-On Technology
>> Corporation Device 21f1 (rev 01) (prog-if 02 [NVM Express])
>>>           Subsystem: Marvell Technology Group Ltd. Device 1093
>>>            <snip>
>>>                   LnkCap: Port #0, Speed 8GT/s, Width x4, ASPM L1, Exit Latency L0s
>> <512ns, L1 <64us
>>>                           ClockPM+ Surprise- LLActRep- BwNot- ASPMOptComp+
>>>                   LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- CommClk+
>>>                           ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
>>>                   LnkSta: Speed 8GT/s, Width x4, TrErr- Train- SlotClk+ DLActive-
>> BWMgmt- ABWMgmt-
>>>                   DevCap2: Completion Timeout: Not Supported, TimeoutDis+, LTR+,
>> OBFF Via message
>>>                   DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR+,
>> OBFF Disabled
>>>                   LnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-
>>>                            Transmit Margin: Normal Operating Range,
>> EnterModifiedCompliance- ComplianceSOS-
>>>                            Compliance De-emphasis: -6dB
>>>                   LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete-,
>> EqualizationPhase1-
>>>                            EqualizationPhase2-, EqualizationPhase3-,
>>> LinkEqualizationRequest-
>>> -----
>>>> - Vidya Sagar
>>>>
>>>>
>>>>>>>>>     - DWC_EQ_PHASE_2_3_DISABLE: To disable GEN3 equalization
>>>>>>>>> phase 2 & 3
>>>>>>>>>
>>>>>>>>> Platform drivers can set these quirks via "quirk" variable of "dw_pcie"
>>>>>>>>> struct.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Anvesh Salveru <anvesh.s@...sung.com>
>>>>>>>>> Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
>>>>>>>>> ---
>>>>>>>>> Patchset v1 can be found at:
>>>>>>>>>     - 1/2: https://urldefense.proofpoint.com/v2/url?u=https-
>>>>
>> 3A__lkml.org_lkml_2019_9_10_443&d=DwIBAg&c=DPL6_X_6JkXFx7AXWqB0tg
>>>> &r=bkWxpLoW-f-
>>>>
>> E3EdiDCCa0_h0PicsViasSlvIpzZvPxs&m=MtEKKeJsQvi2UM1eSZUv2vPLLxrYU0aI1
>>>> Ry4ICIDaiQ&s=s_nPmMNbQFswYRxQgBkeg4H9J_0FEtzRE-0AruC5WI4&e=
>>>>>>>>>     - 2/2:
>>>>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lkml.org_lk
>>>>>>>>> ml
>>>>>>>>>
>>>> _2019_9_10_444&d=DwIBAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=bkWxpLoW-
>> f-
>>>> E3Ed
>>>>>>>>>
>>>> iDCCa0_h0PicsViasSlvIpzZvPxs&m=MtEKKeJsQvi2UM1eSZUv2vPLLxrYU0aI1Ry
>>>>>>>>>
>> 4ICIDaiQ&s=kkfdwcX6bYcLrnJSgw_GcMMGAjnDTMtN2v6svWuANpk&e=
>>>>>>>>>
>>>>>>>>> Changes w.r.t v1:
>>>>>>>>>     - Squashed two patches from v1 into one as suggested by Gustavo
>>>>>>>>>     - Addressed review comments from Andrew
>>>>>>>>>
>>>>>>>>>     drivers/pci/controller/dwc/pcie-designware.c | 12
>>>>>>>>> ++++++++++++ drivers/pci/controller/dwc/pcie-designware.h |  9
>> +++++++++
>>>>>>>>>     2 files changed, 21 insertions(+)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c
>>>>>>>>> b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>>>>> index 7d25102..97fb18d 100644
>>>>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>>>>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>>>>> @@ -466,4 +466,16 @@ void dw_pcie_setup(struct dw_pcie *pci)
>>>>>>>>>     		break;
>>>>>>>>>     	}
>>>>>>>>>     	dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL,
>> val);
>>>>>>>>> +
>>>>>>>>> +	if (pci->quirk & DWC_EQUALIZATION_DISABLE) {
>>>>>>>>> +		val = dw_pcie_readl_dbi(pci,
>> PCIE_PORT_GEN3_RELATED);
>>>>>>>>> +		val |= PORT_LOGIC_GEN3_EQ_DISABLE;
>>>>>>>>> +		dw_pcie_writel_dbi(pci, PCIE_PORT_GEN3_RELATED,
>> val);
>>>>>>>>> +	}
>>>>>>>>> +
>>>>>>>>> +	if (pci->quirk & DWC_EQ_PHASE_2_3_DISABLE) {
>>>>>>>>> +		val = dw_pcie_readl_dbi(pci,
>> PCIE_PORT_GEN3_RELATED);
>>>>>>>>> +		val |= PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE;
>>>>>>>>> +		dw_pcie_writel_dbi(pci, PCIE_PORT_GEN3_RELATED,
>> val);
>>>>>>>>> +	}
>>>>>>>>>     }
>>>>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h
>>>>>>>>> b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>>>>> index ffed084..e428b62 100644
>>>>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>>>>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>>>>> @@ -29,6 +29,10 @@
>>>>>>>>>     #define LINK_WAIT_MAX_IATU_RETRIES	5
>>>>>>>>>     #define LINK_WAIT_IATU			9
>>>>>>>>>
>>>>>>>>> +/* Parameters for GEN3 related quirks */
>>>>>>>>> +#define DWC_EQUALIZATION_DISABLE	BIT(1)
>>>>>>>>> +#define DWC_EQ_PHASE_2_3_DISABLE	BIT(2)
>>>>>>>>> +
>>>>>>>>>     /* Synopsys-specific PCIe configuration registers */
>>>>>>>>>     #define PCIE_PORT_LINK_CONTROL		0x710
>>>>>>>>>     #define PORT_LINK_MODE_MASK		GENMASK(21, 16)
>>>>>>>>> @@ -60,6 +64,10 @@
>>>>>>>>>     #define PCIE_MSI_INTR0_MASK		0x82C
>>>>>>>>>     #define PCIE_MSI_INTR0_STATUS		0x830
>>>>>>>>>
>>>>>>>>> +#define PCIE_PORT_GEN3_RELATED		0x890
>>>>>>>>
>>>>>>>> I hadn't noticed this in the previous version - what is the
>>>>>>>> proper name
>>>>>>> for this
>>>>>>>> register? Does it end in _RELATED?
>>>>>>>
>>>>>>> As per SNPS databook the name of the register is "GEN3_RELATED_OFF".
>>>>>>> It is port logic register so, to keep similarity with other port
>>>>>>> logic registers in this file we named it as "PCIE_PORT_GEN3_RELATED".
>>>>>>
>>>>>> OK.
>>>>>>
>>>>>> Reviewed-by: Andrew Murray <andrew.murray@....com>
>>>>>>
>>>>>> Also is the SNPS databook publicly available? I'd be interested in
>>>>>> reading it.
>>>>>
>>>>> The databook isn't openly available, sorry.
>>>>>
>>>>> Gustavo
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Andrew Murray
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>>
>>>>>>>> Andrew Murray
>>>>>>>>
>>>>>>>>> +#define PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE	BIT(9)
>>>>>>>>> +#define PORT_LOGIC_GEN3_EQ_DISABLE		BIT(16)
>>>>>>>>> +
>>>>>>>>>     #define PCIE_ATU_VIEWPORT		0x900
>>>>>>>>>     #define PCIE_ATU_REGION_INBOUND		BIT(31)
>>>>>>>>>     #define PCIE_ATU_REGION_OUTBOUND	0
>>>>>>>>> @@ -244,6 +252,7 @@ struct dw_pcie {
>>>>>>>>>     	struct dw_pcie_ep	ep;
>>>>>>>>>     	const struct dw_pcie_ops *ops;
>>>>>>>>>     	unsigned int		version;
>>>>>>>>> +	unsigned int		quirk;
>>>>>>>>>     };
>>>>>>>>>
>>>>>>>>>     #define to_dw_pcie_from_pp(port) container_of((port), struct
>>>>>>>>> dw_pcie,
>>>>>>>>> pp)
>>>>>>>>> --
>>>>>>>>> 2.7.4
>>>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>
>>>
> 
>