linux-kernel - Re: [PATCH] PCI: qcom: add missing supplies required for msm8996

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Date:   Tue, 23 Jan 2018 10:33:13 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Stanimir Varbanov <svarbanov@...sol.com>,
        linux-pci@...r.kernel.org, bhelgaas@...gle.com
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        robh+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: add missing supplies required for msm8996



On 23/01/18 10:14, Stanimir Varbanov wrote:
> Hi,
> 
> On 01/23/2018 11:46 AM, Srinivas Kandagatla wrote:
>>
>>
>> On 23/01/18 09:23, Stanimir Varbanov wrote:
>>> Hey Srini,
>>>
>>> As there are no comments I'd propose to change the endpoint supplies to
>>> more generic names.
>>>
>> Sure, I will respin this with your suggestions, except the 3v3 and 1v5
>> suffix due to the reasons below:
>>>> +- vdda-1p8-supply:
>>>> +    Usage: required for msm8996
>>>> +    Value type: <phandle>
>>>> +    Definition: A phandle to the 1.8v analog power supply
>>>> +
>>>
>>> This should be dropped, because it is part of the phy.
>> Yep.
>>
>>>
>>>>    - vdda_phy-supply:
>>>>        Usage: required for ipq/apq8064
>>>>        Value type: <phandle>
>>>> @@ -189,6 +194,15 @@
>>>>        Value type: <phandle>
>>>>        Definition: A phandle to the analog power supply for IC which
>>>> generates
>>>>                reference clock
>>>> +- vddpe-supply:
>>>> +    Usage: optional
>>>> +    Value type: <phandle>
>>>> +    Definition: A phandle to the PCIe endpoint power supply
>>>
>>> vddpe_3v3-supply
>> Why do we need suffix here? AFAIU, It does not add any value, instead it
>> would confuse the users.
> 
> vddpe and vddpe1 is already confusing as well.

I partly agree with you.

How would you represent if there are two power 3v3 supplies for the 
endpoint?

> 
> Lets imagine that powering up the endpointX needs some specific sequence
> between 3v3 and 1v5 and endpointY (which could be connected on the same
> PCIe lane) has different power sequence, how we would handle that in the
> qcom pcie host driver?

power sequencing is all together a different issue, that is not 
addressed in this patch. Am hoping that this will be fixed as part of 
making pwrseq interface more generic. Not sure where it endedup now!!

--srini


> 
>>
>> These are power supplies for endpoint which could be of any voltage. In
> 
> I don't think that could be any values see PCIe mini card
> electromechanical specification. There on the connector are provided 3v3
> and 1v5.
> 
>> this case both endpoint supplies are 3v3, these could be 1.8 or 5v or
>> 12v in some other cases.
> 
> If we see hw designs with 5v and 12v we could extend the binding and the
> driver with support for them. I want to be exact in the names and
> voltages in the driver and bindings.

>