linux-kernel - Re: [PATCH] PCI: cadence: respond to received PTM Requests

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Date:   Tue, 22 Feb 2022 19:40:54 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     Christian Gmeiner <christian.gmeiner@...il.com>,
        <linux-kernel@...r.kernel.org>, Tom Joseph <tjoseph@...ence.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI: cadence: respond to received PTM Requests

Hi Bjorn,

On 18/02/22 6:50 pm, Bjorn Helgaas wrote:
> On Fri, Feb 18, 2022 at 04:26:48PM +0530, Kishon Vijay Abraham I wrote:
>> Hi Bjorn,
>>
>> On 01/02/22 3:35 am, Bjorn Helgaas wrote:
>>> Update subject line to match previous conventions ("git log --oneline
>>> drivers/pci/controller/cadence/pcie-cadence-host.c" to see).
>>>
>>> On Mon, Jan 31, 2022 at 01:08:27PM +0100, Christian Gmeiner wrote:
>>>> This enables the Controller [RP] to automatically respond
>>>> with Response/ResponseD messages.
>>>
> 
>>>> +static void cdns_pcie_host_enable_ptm_response(struct cdns_pcie *pcie)
>>>> +{
>>>> +	u32 val;
>>>> +
>>>> +	val = cdns_pcie_readl(pcie, CDNS_PCIE_LM_PTM_CTRL);
>>>> +	cdns_pcie_writel(pcie, CDNS_PCIE_LM_PTM_CTRL, val | CDNS_PCIE_LM_TPM_CTRL_PTMRSEN);
>>>
>>> I assume this is some device-specific enable bit that is effectively
>>> ANDed with PCI_PTM_CTRL_ENABLE in the Precision Time Measurement
>>> Capability?
>>
>> That's correct. This bit enables Controller [RP] to respond to the
>> received PTM Requests.
> 
> Great!  Christian, can you update the commit log to reflect that
> both this bit *and* PCI_PTM_CTRL_ENABLE must be set for the RP to
> respond to received PTM Requests?
> 
> When CDNS_PCIE_LM_TPM_CTRL_PTMRSEN is cleared, do PCI_PTM_CAP_ROOT
> and the PTM Responder Capable bit (for which we don't have a #define)
> read as zero?

I see both PTM Responder Capable bit and PTM Root Capable is by-default set to '1'.

root@...4xx-evm:~# devmem2 0xD000A24


/dev/mem opened.
Memory mapped at address 0xffffa8980000.
Read at address  0x0D000A24 (0xffffa8980a24): 0x00000406

And this bit can be programmed through the local management APB
interface if required.

But with this patch which enables PTM by default for RC, it wouldn't be required
to clear those bits.

Thanks,
Kishon
> 
> I think that would be the correct behavior per PCIe r6.0, sec
> 7.9.15.2, and it would avoid the confusion of having the PTM
> Capability register advertise functionality that cannot be enabled via
> the PTM Control register.
> 
>>>> +/* PTM Control Register */
>>>> +#define CDNS_PCIE_LM_PTM_CTRL 	(CDNS_PCIE_LM_BASE + 0x0DA8)
> 
> Other #defines in this file use lower-case hex.
> 
> Bjorn
>