linux-kernel - Re: [PATCH 1/1] RFC: dt bindings: Add property "brcm,gen3-eq-presets"

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Message-ID: <36ec01f4-c0fb-188e-06e9-10c7360a8ef0@quicinc.com>
Date: Tue, 29 Oct 2024 10:47:00 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: James Quinlan <james.quinlan@...adcom.com>, Rob Herring <robh@...nel.org>
CC: <linux-pci@...r.kernel.org>, Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi
	<lorenzo.pieralisi@....com>,
        <bcm-kernel-feedback-list@...adcom.com>, <jim2101024@...il.com>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@...aro.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "moderated list:BROADCOM BCM7XXX ARM
 ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>,
        "moderated
 list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE"
	<linux-rpi-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND
 FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>,
        open list
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] RFC: dt bindings: Add property "brcm,gen3-eq-presets"



On 10/29/2024 12:21 AM, James Quinlan wrote:
> On 10/24/24 21:08, Krishna Chaitanya Chundru wrote:
>>
>>
>> On 10/22/2024 12:33 AM, Rob Herring wrote:
>>> On Fri, Oct 18, 2024 at 02:22:45PM -0400, Jim Quinlan wrote:
>>>> Support configuration of the GEN3 preset equalization settings, aka the
>>>> Lane Equalization Control Register(s) of the Secondary PCI Express
>>>> Extended Capability.  These registers are of type HwInit/RsvdP and
>>>> typically set by FW.  In our case they are set by our RC host bridge
>>>> driver using internal registers.
>>>>
>>>> Signed-off-by: Jim Quinlan <james.quinlan@...adcom.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 0925c520195a..f965ad57f32f 100644
>>>> --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
>>>> +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
>>>> @@ -104,6 +104,18 @@ properties:
>>>>       minItems: 1
>>>>       maxItems: 3
>>>>   +  brcm,gen3-eq-presets:
>>>> +    description: |
>>>> +      A u16 array giving the GEN3 equilization presets, one for 
>>>> each lane.
>>>> +      These values are destined for the 16bit registers known as the
>>>> +      Lane Equalization Control Register(s) of the Secondary PCI 
>>>> Express
>>>> +      Extended Capability.  In the array, lane 0 is first term, 
>>>> lane 1 next,
>>>> +      etc. The contents of the entries reflect what is necessary for
>>>> +      the current board and SoC, and the details of each preset are
>>>> +      described in Section 7.27.4 of the PCI base spec, Revision 3.0.
>>>
>>> If these are defined by the PCIe spec, then why is it Broadcom specific
>>> property?
> Yes, I will remove the "brcm," prefix.
>>>
>> Hi Rob,
>>
>> qcom pcie driver also needs to program these presets as you suggested
>> this can go to common pci bridge binding.
>>
>> from PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4.2 for data rates
>> of  8.0 GT/s, 16.0 GT/s, and 32.0 GT/s uses one class of preset (P0
>> through P10) and where as data rates of 64.0 GT/s use different class of
>> presets (Q0 through Q10) (Table 4-23). And data rates of 8.0 GT/s also
>> have optional preset hints (Table 4-24).
>>
>> And there is possibility that for each data rate we may require
>> different preset configuration.
>>
>> Can we have a dt binding for each data rate of 16 byte array.
>> like gen3-eq-preset array, gen4-eq-preset array etc.
> 
> Yes, that was the idea when using "genX-eq-preset", for X in {3,4...}.
> 
> Keep in mind that this is an RFC; I have a backlog of commit submissions 
> before I can submit the code that uses this DT property.  If you 
> (Krishna) want to submit something now I'd be quite happy to go with 
> that.  I don't believe it is acceptable to submit a bindings commit w/o 
> code that uses it (if I'm incorrect I'll be glad to do a V2).
> 
Hi Jim,

I submitted a pull request for this. if you have any other suggestions
or if we need to have any other details we can update this pull request.
https://github.com/devicetree-org/dt-schema/pull/146

- Krishna Chaitanya.
> Regards,
> 
> Jim Quinlan
> Broadcom STB/CM
> 
>>
>> - Krishna Chaitanya
>>>> +
>>>> +    $ref: /schemas/types.yaml#/definitions/uint16-array
>>>
>>> minItems: 1
>>> maxItems: 16
>>>
>>> Last I saw, you can only have up to 16 lanes.
>>>
>>> Rob
>>>
>