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SubjectRE: [PATCH v2] PCI: dwc: Add support to add GEN3 related equalization quirks
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> -----Original Message-----
> From: Vidya Sagar <vidyas@nvidia.com>
> Sent: Tuesday, September 24, 2019 4:57 PM
> To: Pankaj Dubey <pankaj.dubey@samsung.com>; 'Gustavo Pimentel'
> <Gustavo.Pimentel@synopsys.com>; 'Andrew Murray'
> <andrew.murray@arm.com>
> Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org;
> jingoohan1@gmail.com; lorenzo.pieralisi@arm.com; bhelgaas@google.com;
> 'Anvesh Salveru' <anvesh.s@samsung.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@nvidia.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@arm.com>
> >>> wrote:
> >>>
> >>>> On Mon, Sep 16, 2019 at 04:36:33PM +0530, Pankaj Dubey wrote:
> >>>>>
> >>>>>
> >>>>>> -----Original Message-----
> >>>>>> From: Andrew Murray <andrew.murray@arm.com>
> >>>>>> Sent: Monday, September 16, 2019 3:46 PM
> >>>>>> To: Pankaj Dubey <pankaj.dubey@samsung.com>
> >>>>>> Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org;
> >>>>>> jingoohan1@gmail.com; gustavo.pimentel@synopsys.com;
> >>>>>> lorenzo.pieralisi@arm.com; bhelgaas@google.com; Anvesh Salveru
> >>>>>> <anvesh.s@samsung.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@samsung.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.

> > 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@samsung.com>
> >>>>>>> Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.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@arm.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
> >>>>>>>
> >>>>>
> >>>
> >>>
> >
> >


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