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

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Date:   Tue, 29 Mar 2022 10:08:53 -0500
From:   Rob Herring <robh@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     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>,
        Serge Semin <fancer.lancer@...il.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 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.

Rob