It'd be nice to mention the property names (maybe omit the "brcm,"
prefix if that helps) in the commit log so "git log --oneline" is more
useful:
959e000f0463 ("dt-bindings: PCI: brcmstb: Add two optional props")
ea372f45cfff ("dt-bindings: PCI: Add bindings for Brcmstb EP voltage regulators")
504253e44a9d ("dt-bindings: PCI: Correct brcmstb interrupts, interrupt-map.")
145790e55d82 ("dt-bindings: PCI: Add compatible string for Brcmstb 74[23]5 MIPs SOCs")
5e8a7d26d935 ("dt-bindings: PCI: brcmstb: compatible is required")
f435ce7ebf8c ("dt-bindings: PCI: brcmstb: add BCM4908 binding")
On Tue, Apr 11, 2023 at 12:59:16PM -0400, Jim Quinlan wrote:
> Regarding "brcm,enable-l1ss":
>
> The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
> requires the driver probe() to deliberately place the HW one of three
> CLKREQ# modes:
>
> (a) CLKREQ# driven by the RC unconditionally
> (b) CLKREQ# driven by the EP for ASPM L0s, L1
> (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).
>
> The HW+driver can tell the difference between downstream devices that
> need (a) and (b), but does not know when to configure (c). Further, the
> HW may 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. Setting this property only makes sense when the
> downstream device is L1SS-capable and the OS is configured to activate
> this mode (e.g. policy==superpowersave).
>
> This property is already present in the Raspian version of Linux, but the
> upstream driver implementaion that will follow adds more details and
> discerns between (a) and (b).
>
> Regarding "brcm,completion-timeout-us"
>
> Our HW will cause a CPU abort if the L1SS exit time is longer than the
> PCIe transaction completion abort timeout. We've been asked to make this
> configurable, so we are introducing "brcm,completion-timeout-us".
Completion Timeout is a generic PCIe concept. Do we want a generic
(non-brcm) name that would be documented elsewhere? Rob?
> Signed-off-by: Jim Quinlan <jim2101024@xxxxxxxxx>
> ---
> .../devicetree/bindings/pci/brcm,stb-pcie.yaml | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> index 7e15aae7d69e..f7fc2f6561bb 100644
> --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> @@ -64,6 +64,22 @@ properties:
>
> aspm-no-l0s: true
>
> + brcm,enable-l1ss:
> + description: Indicates that PCIe L1SS power savings
> + are desired, the downstream device is L1SS-capable, and the
> + OS has been configured to enable this mode. Note that when
> + in this mode, this particular HW may not meet the requirement
> + that requires CLKREQ# assertion to clock active to be
> + within 400ns.
Maybe a pointer to the source of the 400ns requirement?
"requirement that requires" is a little redundant, maybe "... may not
meet the requirement that Refclk be valid within 400ns of CLKREQ#
assertion"?
(I don't actually know whether this refers to Refclk or if that would
be a true statement; this is just a possible sentence structure.)
