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

[Florian Fainelli]

On 4/6/23 11:35, Krzysztof Kozlowski wrote:
> On 06/04/2023 18:58, Jim Quinlan wrote:
> > On Thu, Apr 6, 2023 at 11:39 AM Stefan Wahren <stefan.wahren@xxxxxxxx> 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@xxxxxxxxx>
> > > > ---
> > > >    .../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.
>
> If "completion" means Linux completion, then it is not suitable for DT
> and entire property should be removed. If it is something else, then
> explain here and commit msg. So far both refer to some completion...

This is a PCIe root complex binding so completion needs to be understood 
in the context of PCIe, that is the time needed for the root complex to 
complete/finish/proceed with a PCIe transaction layer packet (TLP).
--
Florian