linux-kernel - Re: [PATCH 08/12] PCI: dwc: Discard IP-core version checking on unrolled iATU detection

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Date:   Thu, 24 Mar 2022 17:49:05 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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>,
        Rob Herring <robh@...nel.org>,
        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>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/12] PCI: dwc: Discard IP-core version checking on
 unrolled iATU detection

On Thu, Mar 24, 2022 at 04:25:19AM +0300, Serge Semin wrote:
> It's pretty much pointless. Even though unrolled version of the internal
> ATU has been indeed available since DWC PCIe v4.80a IP-core, there is no
> guarantee it was enabled during the IP-core configuration (Synopsys
> suggests to contact the Solvnet support for guidance of how to do that for
> the newer IP-cores). So the only reliable way to find out the unrolled
> iATU feature availability is indeed to check the iATU viewport register
> content. In accordance with the reference manual [1] if the register
> doesn't exist (unrolled iATU is enabled) it's content is fixed with
> 0xff-s, otherwise it will contain some zeros. So we can freely drop the
> IP-core version checking in this matter then and use the
> dw_pcie_iatu_unroll_enabled() method only to detect whether iATU/eDMA
> space is unrolled.
> 
> [1] DesignWare Cores, PCI Express Controller, Register Desciptions,
> v.4.90a, December 2016, p.855
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Thanks,
Mani

> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 3bd1cfd12148..e3d2c11e6998 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -600,15 +600,15 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci, u32 link_gen)
>  
>  }
>  
> -static u8 dw_pcie_iatu_unroll_enabled(struct dw_pcie *pci)
> +static bool dw_pcie_iatu_unroll_enabled(struct dw_pcie *pci)
>  {
>  	u32 val;
>  
>  	val = dw_pcie_readl_dbi(pci, PCIE_ATU_VIEWPORT);
>  	if (val == 0xffffffff)
> -		return 1;
> +		return true;
>  
> -	return 0;
> +	return false;
>  }
>  
>  static void dw_pcie_iatu_detect_regions_unroll(struct dw_pcie *pci)
> @@ -680,9 +680,8 @@ void dw_pcie_iatu_detect(struct dw_pcie *pci)
>  	struct device *dev = pci->dev;
>  	struct platform_device *pdev = to_platform_device(dev);
>  
> -	if (pci->version >= 0x480A || (!pci->version &&
> -				       dw_pcie_iatu_unroll_enabled(pci))) {
> -		pci->iatu_unroll_enabled = true;
> +	pci->iatu_unroll_enabled = dw_pcie_iatu_unroll_enabled(pci);
> +	if (pci->iatu_unroll_enabled) {
>  		if (!pci->atu_base) {
>  			struct resource *res =
>  				platform_get_resource_byname(pdev, IORESOURCE_MEM, "atu");
> -- 
> 2.35.1
>