linux-kernel - RE: [PATCH v2] PCI: Cadence: Add quirk for Gen2 controller to do autonomous speed change.

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Date:   Wed, 30 Sep 2020 17:11:23 +0000
From:   Athani Nadeem Ladkhan <nadeem@...ence.com>
To:     Kishon Vijay Abraham I <kishon@...com>,
        Tom Joseph <tjoseph@...ence.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "robh@...nel.org" <robh@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Milind Parab <mparab@...ence.com>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>
Subject: RE: [PATCH v2] PCI: Cadence: Add quirk for Gen2 controller to do
 autonomous speed change.

Hi Kishon,

> -----Original Message-----
> From: Kishon Vijay Abraham I <kishon@...com>
> Sent: Thursday, September 24, 2020 9:45 AM
> To: Athani Nadeem Ladkhan <nadeem@...ence.com>; Tom Joseph
> <tjoseph@...ence.com>; lorenzo.pieralisi@....com; robh@...nel.org;
> bhelgaas@...gle.com; linux-pci@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Cc: Milind Parab <mparab@...ence.com>; Swapnil Kashinath Jakhade
> <sjakhade@...ence.com>
> Subject: Re: [PATCH v2] PCI: Cadence: Add quirk for Gen2 controller to do
> autonomous speed change.
> 
> EXTERNAL MAIL
> 
> 
> Hi Nadeem,
> 
> On 24/09/20 12:04 am, Nadeem Athani 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@...ence.com>
> > ---
> >  drivers/pci/controller/cadence/pcie-cadence-host.c | 14 ++++++++++++++
> >  drivers/pci/controller/cadence/pcie-cadence.h      | 15 +++++++++++++++
> >  2 files changed, 29 insertions(+)
> >
> > diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > index 4550e0d469ca..a2317614268d 100644
> > --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> > +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> > @@ -83,6 +83,9 @@ 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;
> > +	u16 lnk_ctl;
> >
> >  	/*
> >  	 * Set the root complex BAR configuration register:
> > @@ -111,6 +114,17 @@ 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_readw(pcie, link_cap +
> PCI_EXP_LNKCTL);
> > +		lnk_ctl |= PCI_EXP_LNKCTL_RL;
> > +		cdns_pcie_rp_writew(pcie, link_cap + PCI_EXP_LNKCTL,
> lnk_ctl);
> > +	}
> 
> Is this workaround required for all Cadence controller? If not, enable this
> workaround only for versions which doesn't do autonomous speed change.
No. This is taken care in patch version 3.
> 
> I think this workaround should also be applied only after checking for link
> status (cdns_pcie_link_up()).
Yes. This is taken care in patch version 3.
> 
> And this is also applicable for GEN3/GEN4 controller. So the check should be
> to see the capability of the connected PCIe device and not the controller
> itself.
This is taken care in patch version 3.
> 
> Thanks
> Kishon