linux-kernel - Re: R: R: [PATCH v3 08/11] devicetree: bindings: pci: document PARF params bindings

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Date:   Wed, 20 May 2020 13:01:54 +0300
From:   Stanimir Varbanov <svarbanov@...sol.com>
To:     ansuelsmth@...il.com, 'Rob Herring' <robh@...nel.org>
Cc:     'Bjorn Andersson' <bjorn.andersson@...aro.org>,
        'Andy Gross' <agross@...nel.org>,
        'Bjorn Helgaas' <bhelgaas@...gle.com>,
        'Mark Rutland' <mark.rutland@....com>,
        'Lorenzo Pieralisi' <lorenzo.pieralisi@....com>,
        'Andrew Murray' <amurray@...goodpenguin.co.uk>,
        'Philipp Zabel' <p.zabel@...gutronix.de>,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: R: R: [PATCH v3 08/11] devicetree: bindings: pci: document PARF
 params bindings

Hi,

On 5/13/20 3:56 PM, ansuelsmth@...il.com wrote:
>> On 5/12/20 6:45 PM, Rob Herring wrote:
>>> On Thu, May 07, 2020 at 09:34:35PM +0200, ansuelsmth@...il.com
>> wrote:
>>>>> On Fri, May 01, 2020 at 12:06:15AM +0200, Ansuel Smith wrote:
>>>>>> It is now supported the editing of Tx De-Emphasis, Tx Swing and
>>>>>> Rx equalization params on ipq8064. Document this new optional
>> params.
>>>>>>
>>>>>> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
>>>>>> ---
>>>>>>  .../devicetree/bindings/pci/qcom,pcie.txt     | 36
>> +++++++++++++++++++
>>>>>>  1 file changed, 36 insertions(+)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/pci/qcom,pcie.txt
>>>>> b/Documentation/devicetree/bindings/pci/qcom,pcie.txt
>>>>>> index 6efcef040741..8cc5aea8a1da 100644
>>>>>> --- a/Documentation/devicetree/bindings/pci/qcom,pcie.txt
>>>>>> +++ b/Documentation/devicetree/bindings/pci/qcom,pcie.txt
>>>>>> @@ -254,6 +254,42 @@
>>>>>>  			- "perst-gpios"	PCIe endpoint reset signal line
>>>>>>  			- "wake-gpios"	PCIe endpoint wake signal line
>>>>>>
>>>>>> +- qcom,tx-deemph-gen1:
>>>>>> +	Usage: optional (available for ipq/apq8064)
>>>>>> +	Value type: <u32>
>>>>>> +	Definition: Gen1 De-emphasis value.
>>>>>> +		    For ipq806x should be set to 24.
>>>>>
>>>>> Unless these need to be tuned per board, then the compatible string
>> for
>>>>> ipq806x should imply all these settings.
>>>>>
>>>>
>>>> It was requested by v2 to make this settings tunable. These don't change
>> are
>>>> all the same for every ipq806x SoC. The original implementation had this
>>>> value hardcoded for ipq806x. Should I restore this and drop this patch?
>>>
>>> Yes, please.
>>
>> I still think that the values for tx deemph and tx swing should be
>> tunable. But I can live with them in the driver if they not break
>> support for apq8064.
>>
>> The default values in the registers for apq8064 and ipq806x are:
>>
>> 			default		your change
>> TX_DEEMPH_GEN1		21		24
>> TX_DEEMPH_GEN2_3_5DB	21		24
>> TX_DEEMPH_GEN2_6DB	32		34
>>
>> TX_SWING_FULL		121		120
>> TX_SWING_LOW		121		120
>>
>> So until now (without your change) apq8064 worked with default values.
>>
> 
> I will limit this to ipq8064(-v2) if this could be a problem.

I guess you can do it that way, but if new board appear in the future
with slightly different parameters (for example deemph_gen1 = 23 and so
on) do we need to add another compatible for that? At the end we will
have compatibles per board but not per SoC. :(

-- 
regards,
Stan