linux-kernel - Re: [PATCH 05/16] PCI: dwc: Add IP-core version detection procedure

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Message-ID: <20220417151320.wahjqjbe3efb4kty@mobilestation>
Date:   Sun, 17 Apr 2022 18:13:20 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/16] PCI: dwc: Add IP-core version detection procedure

On Tue, Mar 29, 2022 at 10:08:53AM -0500, Rob Herring wrote:
> On Thu, Mar 24, 2022 at 04:37:23AM +0300, Serge Semin wrote:
> > Since DWC PCIe v4.70a the controller version and version type can be read
> > from the PORT_LOGIC.PCIE_VERSION_OFF and PORT_LOGIC.PCIE_VERSION_TYPE_OFF
> > registers respectively. Seeing the generic code has got version-dependent
> > parts let's use these registers to find out the controller version.  The
> > detection procedure is executed for both RC and EP modes right after the
> > platform-specific initialization. We can't do that earlier since the
> > glue-drivers can perform the DBI-related setups there including the bus
> > reference clocks activation, without which the CSRs just can't be read.
> > 
> > Note the CSRs content is zero on the older DWC PCIe controller. In that
> > case we have no choice but to rely on the platform setup.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > ---
> >  .../pci/controller/dwc/pcie-designware-ep.c   |  2 ++
> >  .../pci/controller/dwc/pcie-designware-host.c |  2 ++
> >  drivers/pci/controller/dwc/pcie-designware.c  | 24 +++++++++++++++++++
> >  drivers/pci/controller/dwc/pcie-designware.h  |  6 +++++
> >  4 files changed, 34 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > index 7c9315fffe24..3b981d13cca9 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > @@ -645,6 +645,8 @@ int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
> >  	u32 reg;
> >  	int i;
> >  
> > +	dw_pcie_version_detect(pci);
> > +
> >  	hdr_type = dw_pcie_readb_dbi(pci, PCI_HEADER_TYPE) &
> >  		   PCI_HEADER_TYPE_MASK;
> >  	if (hdr_type != PCI_HEADER_TYPE_NORMAL) {
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 8364ea234e88..8f0d473ff770 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -398,6 +398,8 @@ int dw_pcie_host_init(struct pcie_port *pp)
> >  		}
> >  	}
> >  
> > +	dw_pcie_version_detect(pci);
> > +
> >  	dw_pcie_iatu_detect(pci);
> >  
> >  	dw_pcie_setup_rc(pp);
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index c21373c6cb51..49c494d82042 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -16,6 +16,30 @@
> >  #include "../../pci.h"
> >  #include "pcie-designware.h"
> >  
> > +void dw_pcie_version_detect(struct dw_pcie *pci)
> > +{
> > +	u32 ver;
> > +
> > +	/* The content of the CSR is zero on DWC PCIe older than v4.70a */
> > +	ver = dw_pcie_readl_dbi(pci, PCIE_VERSION_NUMBER);
> > +	if (!ver)
> > +		return;
> > +
> > +	if (pci->version && pci->version != ver)
> > +		dev_warn(pci->dev, "Versions don't match (%08x != %08x)\n",
> > +			 pci->version, ver);
> 

> Trust the h/w is correct until we have a known case where it isn't. Just 
> read the h/w reg if pci->version is zero.
> 
> I would suspect as-is this will give some warnings. No doubt there is 
> some platform with multiple revs of Si that didn't change their version 
> in the driver. Or the author just guessed on the version that picked the 
> right paths in the driver.

I'm not sure I fully get it. Could you elaborate what you suggest
here?  Do you suggest for me to drop the warnings and rewrite the
pci->{version, type} fields with the values read from the registers if
these fields were set with zeros?

-Sergey

> 
> Rob