RE: [PATCH v3] PCI: cadence: Retrain Link to work around Gen2 training defect.

[Athani Nadeem Ladkhan <nadeem@cadence.com>]

Hi Kishon,

> -----Original Message-----
> From: Kishon Vijay Abraham I <kishon@ti.com>
> Sent: Monday, October 19, 2020 10:59 AM
> To: Athani Nadeem Ladkhan <nadeem@cadence.com>;
> lorenzo.pieralisi@arm.com; robh@kernel.org; bhelgaas@google.com; linux-
> pci@vger.kernel.org; linux-kernel@vger.kernel.org; Tom Joseph
> <tjoseph@cadence.com>
> Cc: Swapnil Kashinath Jakhade <sjakhade@cadence.com>; Milind Parab
> <mparab@cadence.com>
> Subject: Re: [PATCH v3] PCI: cadence: Retrain Link to work around Gen2
> training defect.
> 
> EXTERNAL MAIL
> 
> 
> Hi Nadeem,
> 
> On 30/09/20 11:51 pm, Nadeem Athani wrote:
> > Cadence controller will not initiate autonomous speed change if
> > strapped as Gen2. The Retrain Link bit is set as quirk to enable this speed
> change.
> >
> > Signed-off-by: Nadeem Athani <nadeem@cadence.com>
> > ---
> > Changes in v3:
> > - To set retrain link bit,checking device capability & link status.
> > - 32bit read in place of 8bit.
> > - Minor correction in patch comment.
> > - Change in variable & macro name.
> > Changes in v2:
> > - 16bit read in place of 8bit.
> >  drivers/pci/controller/cadence/pcie-cadence-host.c | 31
> ++++++++++++++++++++++
> >  drivers/pci/controller/cadence/pcie-cadence.h      |  9 ++++++-
> >  2 files changed, 39 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > index 4550e0d469ca..2b2ae4e18032 100644
> > --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > @@ -77,6 +77,36 @@ static struct pci_ops cdns_pcie_host_ops = {
> >  	.write		= pci_generic_config_write,
> >  };
> >
> > +static void cdns_pcie_retrain(struct cdns_pcie *pcie) {
> > +	u32 lnk_cap_sls, pcie_cap_off = CDNS_PCIE_RP_CAP_OFFSET;
> > +	u16 lnk_stat, lnk_ctl;
> > +
> > +	if (!cdns_pcie_link_up(pcie))
> > +		return;
> > +
> 
> Is there a IP version that can be used to check if that quirk is applicable?
There is no such provision.
> > +	/*
> > +	 * Set retrain bit if current speed is 2.5 GB/s,
> > +	 * but the PCIe root port support is > 2.5 GB/s.
> > +	 */
> > +
> > +	lnk_cap_sls = cdns_pcie_readl(pcie, (CDNS_PCIE_RP_BASE +
> pcie_cap_off +
> > +				      PCI_EXP_LNKCAP));
> > +	if ((lnk_cap_sls & PCI_EXP_LNKCAP_SLS) <=
> PCI_EXP_LNKCAP_SLS_2_5GB)
> > +		return;
> > +
> > +	lnk_stat = cdns_pcie_rp_readw(pcie, pcie_cap_off +
> PCI_EXP_LNKSTA);
> > +	if ((lnk_stat & PCI_EXP_LNKSTA_CLS) == PCI_EXP_LNKSTA_CLS_2_5GB)
> {
> > +		lnk_ctl = cdns_pcie_rp_readw(pcie,
> > +					     pcie_cap_off + PCI_EXP_LNKCTL);
> > +		lnk_ctl |= PCI_EXP_LNKCTL_RL;
> > +		cdns_pcie_rp_writew(pcie, pcie_cap_off + PCI_EXP_LNKCTL,
> > +				    lnk_ctl);
> > +
> > +		if (!cdns_pcie_link_up(pcie))
> 
> Should this rather be a cdns_pcie_host_wait_for_link()?
The use of this api cdns_pcie_link_up was mentioned in earlier reviews.
The mentioned api cdns_pcie_host_wait_for_link is a wrapper in which there are multiple checks.
If insist, will replace with it.
Thanks,
Nadeem
> 
> Thanks
> Kishon
> 
> > +			return;
> > +	}
> > +}
> >
> >  static int cdns_pcie_host_init_root_port(struct cdns_pcie_rc *rc)  {
> > @@ -115,6 +145,7 @@ static int cdns_pcie_host_init_root_port(struct
> cdns_pcie_rc *rc)
> >  	cdns_pcie_rp_writeb(pcie, PCI_CLASS_PROG, 0);
> >  	cdns_pcie_rp_writew(pcie, PCI_CLASS_DEVICE,
> PCI_CLASS_BRIDGE_PCI);
> >
> > +	cdns_pcie_retrain(pcie);
> >  	return 0;
> >  }
> >
> > diff --git a/drivers/pci/controller/cadence/pcie-cadence.h
> > b/drivers/pci/controller/cadence/pcie-cadence.h
> > index feed1e3038f4..5f1cf032ae15 100644
> > --- a/drivers/pci/controller/cadence/pcie-cadence.h
> > +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> > @@ -119,7 +119,7 @@
> >   * Root Port Registers (PCI configuration space for the root port function)
> >   */
> >  #define CDNS_PCIE_RP_BASE	0x00200000
> > -
> > +#define CDNS_PCIE_RP_CAP_OFFSET 0xc0
> >
> >  /*
> >   * Address Translation Registers
> > @@ -413,6 +413,13 @@ static inline void cdns_pcie_rp_writew(struct
> cdns_pcie *pcie,
> >  	cdns_pcie_write_sz(addr, 0x2, value);  }
> >
> > +static inline u16 cdns_pcie_rp_readw(struct cdns_pcie *pcie, u32 reg)
> > +{
> > +	void __iomem *addr = pcie->reg_base + CDNS_PCIE_RP_BASE + reg;
> > +
> > +	return cdns_pcie_read_sz(addr, 0x2); }
> > +
> >  /* Endpoint Function register access */  static inline void
> > cdns_pcie_ep_fn_writeb(struct cdns_pcie *pcie, u8 fn,
> >  					  u32 reg, u8 value)
> >