linux-kernel - RE: [PATCH 2/2] PCI: dwc: Add support to disable equalization phase 2 and 3

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Message-ID: <23be01d5695f$804e4380$80eaca80$@samsung.com>
Date:   Thu, 12 Sep 2019 17:14:53 +0530
From:   "Pankaj Dubey" <pankaj.dubey@...sung.com>
To:     "'Andrew Murray'" <andrew.murray@....com>
Cc:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "'Jingoo Han'" <jingoohan1@...il.com>,
        <gustavo.pimentel@...opsys.com>, <lorenzo.pieralisi@....com>,
        "'Bjorn Helgaas'" <bhelgaas@...gle.com>,
        "'Anvesh Salveru'" <anvesh.s@...sung.com>
Subject: RE: [PATCH 2/2] PCI: dwc: Add support to disable equalization phase
 2 and 3



> From: Andrew Murray <andrew.murray@....com>
> 
> On Tue, Sep 10, 2019 at 09:51:41PM +0530, Pankaj Dubey wrote:
> > On Tue, 10 Sep 2019 at 19:59, Andrew Murray <andrew.murray@....com>
> wrote:
> > >
> > > On Tue, Sep 10, 2019 at 05:55:02PM +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 high 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.
> > >
> > > Do some platforms have issues conducting phase 2 and 3 when they
> > > successfully conduct phase 0 and 1?
> > >
> >
> > Yes, it is possible.
> >
> > > >
> > > > Platform drivers can disable equalization phase 2 and 3, by
> > > > setting dwc_pci_quirk flag DWC_EQUALIZATION_DISABLE.
> > > >
> > > > Signed-off-by: Anvesh Salveru <anvesh.s@...sung.com>
> > > > Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> > > > ---
> > > >  drivers/pci/controller/dwc/pcie-designware.c | 3 +++
> > > > drivers/pci/controller/dwc/pcie-designware.h | 2 ++
> > > >  2 files changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c
> > > > b/drivers/pci/controller/dwc/pcie-designware.c
> > > > index bf82091..97a8268 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > @@ -472,5 +472,8 @@ void dw_pcie_setup(struct dw_pcie *pci)
> > > >       if (pci->dwc_pci_quirk & DWC_EQUALIZATION_DISABLE)
> > > >               val |= PORT_LOGIC_GEN3_EQ_DISABLE;
> > > >
> > > > +     if (pci->dwc_pci_quirk & DWC_EQ_PHASE_2_3_DISABLE)
> > > > +             val |= PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE;
> > > > +
> 
> Also is it harmless to set both DWC_EQUALIZATION_DISABLE and
> DWC_EQ_PHASE_2_3_DISABLE? (Which is permitted here).
> 

Yes, it will be harmless.

> Thanks,
> 
> Andrew Murray
> 
> > > >       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 a1453c5..b541508 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > > @@ -31,6 +31,7 @@
> > > >
> > > >  /* Parameters for PCIe Quirks */
> > > >  #define DWC_EQUALIZATION_DISABLE     0x1
> > > > +#define DWC_EQ_PHASE_2_3_DISABLE     0x2
> > >
> > > It only makes sense for either DWC_EQUALIZATION_DISABLE or
> > > DWC_EQ_PHASE_2_3_DISABLE to be specified, though if dwc_pci_quirk
> > > intends to hold other quirks should these be numbers and not bit
fields?
> > >
> > Yes, you are right in a given platform it will be either
> > DWC_EQUALIZATION_DISABLE or DWC_EQ_PHASE_2_3_DISABLE.
> >
> > Intention behind making it bit-field was to add other quirks in future.
> >
> > > Thanks,
> > >
> > > Andrew Murray
> > >
> > > >
> > > >  /* Synopsys-specific PCIe configuration registers */
> > > >  #define PCIE_PORT_LINK_CONTROL               0x710
> > > > @@ -65,6 +66,7 @@
> > > >
> > > >  #define PCIE_PORT_GEN3_RELATED               0x890
> > > >  #define PORT_LOGIC_GEN3_EQ_DISABLE   BIT(16)
> > > > +#define PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE BIT(9)
> > > >
> > > >  #define PCIE_ATU_VIEWPORT            0x900
> > > >  #define PCIE_ATU_REGION_INBOUND              BIT(31)
> > > > --
> > > > 2.7.4
> > > >