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

Stefan Wahren
2023-04-06T15:39:29Z

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.

> + 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?

Best regards

> +
> brcm,scb-sizes:
> description: u64 giving the 64bit PCIe memory
> viewport size of a memory controller. There may be up to