linux-kernel - Re: [PATCH V5 04/16] PCI: dwc: Perform dbi regs write lock towards the end

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Date:   Fri, 3 May 2019 13:13:03 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com, robh+dt@...nel.org,
        mark.rutland@....com, jonathanh@...dia.com, kishon@...com,
        catalin.marinas@....com, will.deacon@....com, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com, mperttunen@...dia.com,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V5 04/16] PCI: dwc: Perform dbi regs write lock towards
 the end

On Wed, Apr 24, 2019 at 10:49:52AM +0530, Vidya Sagar 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 [v4]:
> * None
> 
> Changes since [v3]:
> * None
> 
> 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 36fd3f5b48f6..e5e3571dd2fe 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -654,7 +654,6 @@ 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);
> @@ -686,8 +685,6 @@ 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 */

Perhaps make this explicit by moving the write enable call to the
beginning of the function and the write disable call to the end?

Currently it's pretty difficult to see where it's being disabled. Also,
that would make it more resilient against instantiations that require a
different register to be programmed with writes enabled.

Thierry

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