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

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Date:   Fri, 18 Feb 2022 14:42:24 +0100
From:   Christian Gmeiner <christian.gmeiner@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        LKML <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,

Am Fr., 18. Feb. 2022 um 14:20 Uhr schrieb Bjorn Helgaas <helgaas@...nel.org>:
>
> 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?
>

Would something like this work for you?

---8<---
PCI: cadence: Enable Controller to respond to received PTM Requests

This enables the Controller [RP] to automatically respond with
Response/ResponseD messages if CDNS_PCIE_LM_TPM_CTRL_PTMRSEN
and PCI_PTM_CTRL_ENABLE bits are both set.
---8<---

> 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 can test this out if needed for this change.. but that won't happen
before Monday.

> 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.

I changed this in V2.


-- 
greets
--
Christian Gmeiner, MSc

https://christian-gmeiner.info/privacypolicy