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

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Message-ID: <2544621a-4c88-3f3e-786c-7ee8103e132d@nvidia.com>
Date:   Tue, 7 May 2019 13:19:32 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Thierry Reding <thierry.reding@...il.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 5/3/2019 4:43 PM, Thierry Reding wrote:
> 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.
Agree. I'll move enabling write to beginning of this function and disabling
to the end in the next patch series.

> 
> Thierry
>