RE: [PATCH] PCI: Cadence: Add quirk for Gen2 controller to do autonomous speed change.

[Athani Nadeem Ladkhan]

Hi Rob,

> -----Original Message-----
> From: Rob Herring <robh@xxxxxxxxxx>
> Sent: Tuesday, September 22, 2020 11:08 PM
> To: Athani Nadeem Ladkhan <nadeem@xxxxxxxxxxx>
> Cc: Tom Joseph <tjoseph@xxxxxxxxxxx>; Lorenzo Pieralisi
> <lorenzo.pieralisi@xxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; PCI
> <linux-pci@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Milind Parab
> <mparab@xxxxxxxxxxx>; Swapnil Kashinath Jakhade
> <sjakhade@xxxxxxxxxxx>
> Subject: Re: [PATCH] PCI: Cadence: Add quirk for Gen2 controller to do
> autonomous speed change.
> 
> EXTERNAL MAIL
> 
> 
> On Fri, Sep 18, 2020 at 4:34 AM Nadeem Athani <nadeem@xxxxxxxxxxx>
> wrote:
> >
> > Cadence controller will not initiate autonomous speed change if
> > strapped as Gen2. The Retrain bit is set as a quirk to trigger this
> > speed change.
> >
> > Signed-off-by: Nadeem Athani <nadeem@xxxxxxxxxxx>
> > ---
> >  drivers/pci/controller/cadence/pcie-cadence-host.c |   13 +++++++++++++
> >  drivers/pci/controller/cadence/pcie-cadence.h      |    6 ++++++
> >  2 files changed, 19 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > index 4550e0d..4cb7f29 100644
> > --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > @@ -83,6 +83,8 @@ static int cdns_pcie_host_init_root_port(struct
> cdns_pcie_rc *rc)
> >         struct cdns_pcie *pcie = &rc->pcie;
> >         u32 value, ctrl;
> >         u32 id;
> > +       u32 link_cap = CDNS_PCIE_LINK_CAP_OFFSET;
> > +       u8 sls, lnk_ctl;
> >
> >         /*
> >          * Set the root complex BAR configuration register:
> > @@ -111,6 +113,17 @@ static int cdns_pcie_host_init_root_port(struct
> cdns_pcie_rc *rc)
> >         if (rc->device_id != 0xffff)
> >                 cdns_pcie_rp_writew(pcie, PCI_DEVICE_ID,
> > rc->device_id);
> >
> > +       /* Quirk to enable autonomous speed change for GEN2 controller */
> > +       /* Reading Supported Link Speed value */
> > +       sls = PCI_EXP_LNKCAP_SLS &
> > +               cdns_pcie_rp_readb(pcie, link_cap + PCI_EXP_LNKCAP);
> > +       if (sls == PCI_EXP_LNKCAP_SLS_5_0GB) {
> > +               /* Since this a Gen2 controller, set Retrain Link(RL) bit */
> > +               lnk_ctl = cdns_pcie_rp_readb(pcie, link_cap + PCI_EXP_LNKCTL);
> > +               lnk_ctl |= PCI_EXP_LNKCTL_RL;
> > +               cdns_pcie_rp_writeb(pcie, link_cap + PCI_EXP_LNKCTL,
> > + lnk_ctl);
> 
> Why the byte accesses? This is a 16-bit register.
This is a 32bit register. But the register field require is at first byte only. Hence the byte access.
> 
> > +       }
> > +
> >         cdns_pcie_rp_writeb(pcie, PCI_CLASS_REVISION, 0);
> >         cdns_pcie_rp_writeb(pcie, PCI_CLASS_PROG, 0);
> >         cdns_pcie_rp_writew(pcie, PCI_CLASS_DEVICE,
> > PCI_CLASS_BRIDGE_PCI); diff --git
> > a/drivers/pci/controller/cadence/pcie-cadence.h
> > b/drivers/pci/controller/cadence/pcie-cadence.h
> > index feed1e3..075c263 100644
> > --- a/drivers/pci/controller/cadence/pcie-cadence.h
> > +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> > @@ -120,6 +120,7 @@
> >   */
> >  #define CDNS_PCIE_RP_BASE      0x00200000
> >
> > +#define CDNS_PCIE_LINK_CAP_OFFSET 0xC0
> >
> >  /*
> >   * Address Translation Registers
> > @@ -413,6 +414,11 @@ static inline void cdns_pcie_rp_writew(struct
> cdns_pcie *pcie,
> >         cdns_pcie_write_sz(addr, 0x2, value);  }
> >
> > +static inline u8 cdns_pcie_rp_readb(struct cdns_pcie *pcie, u32 reg)
> > +{
> > +       return readb(pcie->reg_base + CDNS_PCIE_RP_BASE + reg); }
> > +
> >  /* Endpoint Function register access */  static inline void
> > cdns_pcie_ep_fn_writeb(struct cdns_pcie *pcie, u8 fn,
> >                                           u32 reg, u8 value)
> > --
> > 1.7.1
> >