linux-kernel - RE: [PATCH V3 04/16] PCI: dwc: Perform dbi regs write lock towards the end

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Date:   Wed, 17 Apr 2019 09:56:33 +0000
From:   Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
To:     Vidya Sagar <vidyas@...dia.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "kishon@...com" <kishon@...com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "gustavo.pimentel@...opsys.com" <Gustavo.Pimentel@...opsys.com>
CC:     "mperttunen@...dia.com" <mperttunen@...dia.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kthota@...dia.com" <kthota@...dia.com>,
        "mmaddireddy@...dia.com" <mmaddireddy@...dia.com>,
        "sagar.tv@...il.com" <sagar.tv@...il.com>
Subject: RE: [PATCH V3 04/16] PCI: dwc: Perform dbi regs write lock towards
 the end

On Tue, Apr 16, 2019 at 20:27:18, Vidya Sagar <vidyas@...dia.com> wrote:

> Remove multiple write enable and disable sequences of dbi registers as
> Tegra194 implements writes to BAR-0 register (offset: 0x10) controlled by
> DBI write-lock enable bit thereby not allowing any further writes to BAR-0
> register in config space to take place. Hence disabling write permission
> only towards the end.
> 
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> Changes since [v2]:
> * None
> 
> Changes since [v1]:
> * None
> 
>  drivers/pci/controller/dwc/pcie-designware-host.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 2a5332e5ccfa..c0334c92c1a6 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -683,7 +683,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
>  	val &= 0xffff00ff;
>  	val |= 0x00000100;
>  	dw_pcie_writel_dbi(pci, PCI_INTERRUPT_LINE, val);
> -	dw_pcie_dbi_ro_wr_dis(pci);
>  
>  	/* Setup bus numbers */
>  	val = dw_pcie_readl_dbi(pci, PCI_PRIMARY_BUS);
> @@ -723,8 +722,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
>  
>  	dw_pcie_wr_own_conf(pp, PCI_BASE_ADDRESS_0, 4, 0);
>  
> -	/* Enable write permission for the DBI read-only register */
> -	dw_pcie_dbi_ro_wr_en(pci);
>  	/* Program correct class for RC */
>  	dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2, PCI_CLASS_BRIDGE_PCI);
>  	/* Better disable write permission right after the update */
> -- 
> 2.17.1

This setup sequence was written by Jingoo Han, let's check if he did this 
by some particular reason.
Jingoo do you remember why you wrote the code like this?

Regards,
Gustavo