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

Jim Quinlan
2023-04-06T16:59:16Z

On Thu, Apr 6, 2023 at 11:39 AM Stefan Wahren <stefan.wahren@i2se.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@gmail.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