linux-kernel - Re: [PATCH v1 1/3] dt-bindings: PCI: brcmstb: Add two optional props

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Message-ID: <CANCKTBsLxkPb1ajACkyhJk6J1aB2iwX0oKifHkADG0fFPUqMhQ@mail.gmail.com>
Date:   Thu, 6 Apr 2023 12:58:59 -0400
From:   Jim Quinlan <jim2101024@...il.com>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     linux-pci@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cyril Brulebois <kibi@...ian.org>,
        Phil Elwell <phil@...pberrypi.com>,
        bcm-kernel-feedback-list@...adcom.com, james.quinlan@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.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:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/3] dt-bindings: PCI: brcmstb: Add two optional props

On Thu, Apr 6, 2023 at 11:39 AM Stefan Wahren <stefan.wahren@...e.com> wrote:
>
> Hi Jim,
>
> Am 06.04.23 um 14:46 schrieb Jim Quinlan:
> > Regarding "brcm,enable-l1ss":
> >
> >    The Broadcom STB/CM PCIe HW -- which is also used by RPi SOCs -- requires
> >    the driver probe to configure one of three clkreq# modes:
> >
> >    (a) clkreq# driven by the RC
> >    (b) clkreq# driven by the EP for ASPM L0s, L1
> >    (c) bidirectional clkreq#, as used for L1 Substates (L1SS).
> >
> >    The HW can tell the difference between (a) and (b), but does not know
> >    when to configure (c).  Further, the HW will cause a CPU abort on boot if
> >    guesses wrong regarding the need for (c).  So we introduce the boolean
> >    "brcm,enable-l1ss" property to indicate that (c) is desired.  This
> >    property is already present in the Raspian version of Linux, but the
> >    driver implementaion that will follow adds more details and discerns
> >    between (a) and (b).
> >
> > Regarding "brcm,completion-timeout-msecs"
> >
> >    Our HW will cause a CPU abort if the L1SS exit time is longer than the
> >    completion abort timeout.  We've been asked to make this configurable, so
> >    we are introducing "brcm,completion-abort-msecs".
> >
> > Signed-off-by: Jim Quinlan <jim2101024@...il.com>
> > ---
> >   .../devicetree/bindings/pci/brcm,stb-pcie.yaml       | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > index 7e15aae7d69e..ef4ccc05b258 100644
> > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > @@ -64,6 +64,18 @@ properties:
> >
> >     aspm-no-l0s: true
> >
> > +  brcm,enable-l1ss:
> > +    description: Indicates that the downstream device is L1SS
> > +      capable and L1SS is desired, e.g. by setting
> > +      CONFIG_PCIEASPM_POWER_SUPERSAVE=y.  Note that CLKREQ#
>
> not sure about this, but maybe we should avoid references to Linux
> kernel config parameter in a DT binding. Since the driver already gaves
> warning in case the DT parameter is present, but kernel config doesn't
> fit, this should be enough.

Hello Stefan,
I will remove this reference.
>
> > +      assertion to clock active must be within 400ns.
> > +    type: boolean
> > +
> > +  brcm,completion-timeout-msecs:
> > +    description: Number of msecs before completion timeout
> > +      abort occurs.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
>
> According to the driver at least 0 is not allowed, maybe we should
> define minimum and maximum here and let dtbs_check take care of invalid
> values?
I'm not sure I follow what you mean about a zero value;  the property
may have any value but the driver will clamp it
to a minimum of ~30msec.  Regardless, I can add a  "minimum: 30" line
to the YAML.

Thanks,
Jim Quinlan
Broadcom STB
>
> Best regards
>
> > +
> >     brcm,scb-sizes:
> >       description: u64 giving the 64bit PCIe memory
> >         viewport size of a memory controller.  There may be up to