linux-kernel - Re: [PATCH v6 3/5] PCI: brcmstb: Set higher value for internal bus timeout

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Date:   Mon, 14 Aug 2023 15:30:07 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cyril Brulebois <kibi@...ian.org>,
        Phil Elwell <phil@...pberrypi.com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jim Quinlan <jim2101024@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 3/5] PCI: brcmstb: Set higher value for internal bus timeout

On Fri, Jul 28, 2023 at 12:15 PM Jim Quinlan <james.quinlan@...adcom.com> wrote:
>
>
>
> On Thu, Jul 27, 2023, 10:44 PM Lorenzo Pieralisi <lpieralisi@...nel.org> wrote:
>>
>> On Fri, Jun 23, 2023 at 10:40:56AM -0400, Jim Quinlan wrote:
>> > During long periods of the PCIe RC HW being in an L1SS sleep state, there
>> > may be a timeout on an internal bus access, even though there may not be
>> > any PCIe access involved.  Such a timeout will cause a subsequent CPU
>> > abort.
>> >
>> > So, when "brcm,enable-l1ss" is observed, we increase the timeout value to
>> > four seconds instead of using its HW default.
>> >
>> > Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
>> > Tested-by: Florian Fainelli <f.fainelli@...il.com>
>> > ---
>> >  drivers/pci/controller/pcie-brcmstb.c | 16 ++++++++++++++++
>> >  1 file changed, 16 insertions(+)
>> >
>> > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
>> > index d30636a725d7..fe0415a98c63 100644
>> > --- a/drivers/pci/controller/pcie-brcmstb.c
>> > +++ b/drivers/pci/controller/pcie-brcmstb.c
>> > @@ -1034,6 +1034,21 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
>> >       return 0;
>> >  }
>> >
>> > +/*
>> > + * This extends the timeout period for an access to an internal bus.  This
>> > + * access timeout may occur during L1SS sleep periods even without the
>> > + * presence of a PCIe access.
>> > + */
>> > +static void brcm_extend_rbus_timeout(struct brcm_pcie *pcie)
>> > +{
>> > +     /* TIMEOUT register is two registers before RGR1_SW_INIT_1 */
>> > +     const unsigned int REG_OFFSET = PCIE_RGR1_SW_INIT_1(pcie) - 8;
>>
>> Nit: you could define an offset for the TIMEOUT register, if that makes
>> it any cleaner, up to you.
>>
>> > +     u32 timeout_us = 4000000; /* 4 seconds, our setting for L1SS */
>>
>> It would be useful to describe why this has to be 4 seconds in case
>> someone in the future will have to change it.
>
>
> Hello,
> IIRC our customer requested 2s and we doubled it.  Bjorn, can you please add this comment or a paraphrase of it before applying -- I'm currently on vacation.

Hello Bjorn,

Is the above request okay with you?  What is the status of these
commits -- will they be applied to pci-next in the near future?

Regards,
Jim Quinlan
Broadcom STB

>
> Regards,
> Jim Quinlan
>
>>
>> Thanks,
>> Lorenzo
>>
>> > +     /* Each unit in timeout register is 1/216,000,000 seconds */
>> > +     writel(216 * timeout_us, pcie->base + REG_OFFSET);
>> > +}
>> > +
>> >  static void brcm_config_clkreq(struct brcm_pcie *pcie)
>> >  {
>> >       bool l1ss = of_property_read_bool(pcie->np, "brcm,enable-l1ss");
>> > @@ -1059,6 +1074,7 @@ static void brcm_config_clkreq(struct brcm_pcie *pcie)
>> >                * of 400ns, as specified in 3.2.5.2.2 of the PCI Express
>> >                * Mini CEM 2.0 specification.
>> >                */
>> > +             brcm_extend_rbus_timeout(pcie);
>> >               clkreq_set |= PCIE_MISC_HARD_PCIE_HARD_DEBUG_L1SS_ENABLE_MASK;
>> >               dev_info(pcie->dev, "bi-dir CLKREQ# for L1SS power savings");
>> >       } else {
>> > --
>> > 2.17.1
>> >
>>
>>

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