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

Krzysztof Kozlowski
2023-04-06T18:55:16Z

On 06/04/2023 20:53, Florian Fainelli wrote:
> On 4/6/23 11:34, Krzysztof Kozlowski wrote:
>> On 06/04/2023 14:46, Jim Quinlan wrote:
>>> 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#
>>
>> How does CONFIG_PCIEASPM_POWER_SUPERSAVE apply to *BSD?
>
> In other words, there should be no OS/Linux specific comments in a
> Device Tree binding, which would be a friendlier and nicer way of
> providing the same feedback.

I want to give also the answer also why there should be no OS/Linux
specific comments, so the reader can stop a bit and think about it :)

Best regards,
Krzysztof