Re: [PATCH V11 03/12] PCI: dwc: Perform dbi regs write lock towards the end

From: Vidya Sagar <vidyas@nvidia.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: <bhelgaas@google.com>, <robh+dt@kernel.org>,
	<mark.rutland@arm.com>, <thierry.reding@gmail.com>,
	<jonathanh@nvidia.com>, <kishon@ti.com>,
	<catalin.marinas@arm.com>, <will.deacon@arm.com>,
	<jingoohan1@gmail.com>, <gustavo.pimentel@synopsys.com>,
	<digetx@gmail.com>, <mperttunen@nvidia.com>,
	<linux-pci@vger.kernel.org>, <devicetree@vger.kernel.org>,
	<linux-tegra@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <kthota@nvidia.com>,
	<mmaddireddy@nvidia.com>, <sagar.tv@gmail.com>
Subject: Re: [PATCH V11 03/12] PCI: dwc: Perform dbi regs write lock towards the end
Date: Thu, 27 Jun 2019 22:22:03 +0530	[thread overview]
Message-ID: <fbef2fee-1ca9-b894-6d1a-f2a9449968a5@nvidia.com> (raw)
In-Reply-To: <20190627155047.GF3782@e121166-lin.cambridge.arm.com>

On 6/27/2019 9:20 PM, Lorenzo Pieralisi wrote:
> On Thu, Jun 27, 2019 at 09:03:08PM +0530, Vidya Sagar wrote:
>> On 6/27/2019 8:28 PM, Lorenzo Pieralisi wrote:
>>> On Mon, Jun 24, 2019 at 02:44:56PM +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 enabling write permission at
>>>> the start of function and disabling the same only towards the end.
>>>
>>> I do not understand what this patch does, I would like to rephrase
>>> the commit log in a way that is easier to parse.
>>>
>>> In particular I do not get what you mean in relation to BAR-0, I am
>>> confused, please clarify.
>>>
>>> Lorenzo
>> Well, some of the Synopsys DesignWare core's DBI registers are
>> protected with a lock without which, they are read-only by default.
>> Existing code in dw_pcie_setup_rc() API tries to unlock and lock
>> multiple times whenever it wants to update those write-protected
>> registers. This patch attempts to unlock all such write-protected
>> registers for writing once in the beginning of the function and lock
>> them back towards the end.  As far as BAR-0 register (which is at
>> offset 0x10 in DBI space... nothing but the config space) in Tegra194
>> is concerned, it is one of those registers to which writes are
>> protected. I could have added unlock/lock pair around accessing this
>> register, but that would bloat this API with one more pair of
>> unlock/lock, instead I chose to remove unlock/lock pairs for all
>> protected registers and have unlock in the beginning and lock towards
>> the end.
> 
> Ok, so DBI space registers that require write permissions are per-IP.
> This is clearer so the commit log must be rewritten, it is not clear at
> all in this respect at least not as-is, if you read it you will
> notice ;-)
Ok. I'll update commit message in next patch series.

-Vidya Sagar
> 
> Lorenzo
> 
>>
>> -Vidya Sagar
>>
>>>
>>>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>>>> Reviewed-by: Thierry Reding <treding@nvidia.com>
>>>> Acked-by: Jingoo Han <jingoohan1@gmail.com>
>>>> ---
>>>> Changes since [v10]:
>>>> * None
>>>>
>>>> Changes since [v9]:
>>>> * None
>>>>
>>>> Changes since [v8]:
>>>> * None
>>>>
>>>> Changes since [v7]:
>>>> * None
>>>>
>>>> Changes since [v6]:
>>>> * None
>>>>
>>>> Changes since [v5]:
>>>> * Moved write enable to the beginning of the API and write disable to the end
>>>>
>>>> Changes since [v4]:
>>>> * None
>>>>
>>>> Changes since [v3]:
>>>> * None
>>>>
>>>> Changes since [v2]:
>>>> * None
>>>>
>>>> Changes since [v1]:
>>>> * None
>>>>
>>>>    drivers/pci/controller/dwc/pcie-designware-host.c | 14 ++++++++------
>>>>    1 file changed, 8 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
>>>> index f93252d0da5b..d3156446ff27 100644
>>>> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
>>>> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
>>>> @@ -628,6 +628,12 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
>>>>    	u32 val, ctrl, num_ctrls;
>>>>    	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>>>> +	/*
>>>> +	 * Enable DBI read-only registers for writing/updating configuration.
>>>> +	 * Write permission gets disabled towards the end of this function.
>>>> +	 */
>>>> +	dw_pcie_dbi_ro_wr_en(pci);
>>>> +
>>>>    	dw_pcie_setup(pci);
>>>>    	if (!pp->ops->msi_host_init) {
>>>> @@ -650,12 +656,10 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
>>>>    	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_1, 0x00000000);
>>>>    	/* Setup interrupt pins */
>>>> -	dw_pcie_dbi_ro_wr_en(pci);
>>>>    	val = dw_pcie_readl_dbi(pci, PCI_INTERRUPT_LINE);
>>>>    	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);
>>>> @@ -687,15 +691,13 @@ 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 */
>>>> -	dw_pcie_dbi_ro_wr_dis(pci);
>>>>    	dw_pcie_rd_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, &val);
>>>>    	val |= PORT_LOGIC_SPEED_CHANGE;
>>>>    	dw_pcie_wr_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, val);
>>>> +
>>>> +	dw_pcie_dbi_ro_wr_dis(pci);
>>>>    }
>>>>    EXPORT_SYMBOL_GPL(dw_pcie_setup_rc);
>>>> -- 
>>>> 2.17.1
>>>>
>>