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

Florian Fainelli
2023-04-06T18:48:44Z

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@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.
>
> 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