linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: x1e80100: Make the PCIe 6a PHY support 4 lanes mode

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Date: Tue, 4 Jun 2024 14:55:31 +0200
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Abel Vesa <abel.vesa@...aro.org>
Cc: Johan Hovold <johan@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Rajendra Nayak
 <quic_rjendra@...cinc.com>, Sibi Sankar <quic_sibis@...cinc.com>,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: qcom: x1e80100: Make the PCIe 6a PHY
 support 4 lanes mode



On 6/4/24 14:45, Abel Vesa wrote:
> On 24-06-04 14:38:40, Konrad Dybcio wrote:
>>
>>
>> On 6/4/24 14:20, Johan Hovold wrote:
>>> On Tue, Jun 04, 2024 at 02:00:10PM +0200, Konrad Dybcio wrote:
>>>> On 6/3/24 14:52, Johan Hovold wrote:
>>>
>>>>> As I just mentioned in my reply on the PHY patch, this does not seem to
>>>>> work on the CRD were the link still come up as 2-lane (also with the
>>>>> clocks fixed):
>>>>>
>>>>> 	qcom-pcie 1bf8000.pci: PCIe Gen.4 x2 link up
>>>>>
>>>>> So something appears to be wrong here or in the PHY changes.
>>>>
>>>> Is the device on the other end x4-capable? Or does it not matter in
>>>> this log line?
>>>
>>> Yes, of course. It's the CRD as I wrote above, and you can tell from
>>> other log entries:
>>>
>>> 	pci 0007:01:00.0: 31.506 Gb/s available PCIe bandwidth, limited by 16.0 GT/s PCIe x2 link at 0007:00:00.0 (capable of 63.012 Gb/s with 16.0 GT/s PCIe x4 link)
>>>
>>> lspci and what Windows reports.
>> Ok, good. I was scared of double-sourcing of parts that are not identical
>> in spec..
>>
> 
> On my CRD, there is a KBG50ZNS256G.
> 
>> [1] suggests this wasn't ever achieved.. which makes the cover letter of
>> this series a bit misleading..
> 
> True ...
> 
>>
>> What does the TCSR check return? If 0, can you hardcode it to 1 and see if
>> the link comes up at x4?
> 
> TCSR check returns 1. But that is not enough. The PCIe controller needs to
> handles some stuff about margining. See the following patchset.
> 
> https://lore.kernel.org/linux-pci/20240501163610.8900-3-quic_schintav@quicinc.com/
> 
> But even with this, I'm not able to get 4-lanes mode to work (yet).
> So it must be something else in the controller driver that is needed.

The margining settings AFAIU shouldn't be necessary for just getting the
link, but to ensure there aren't many errors while transacting..

> 
> IIRC, this is the first Qualcomm platform that would support Gen4 with
> 4-lanes upstream. Maybe I'm wrong.

Seems so

Another idea I had, maybe the PCIE_PORT_LINK_CONTROL &
PCIE_LINK_WIDTH_SPEED_CONTROL registers differ on qcom gen4 controllers..

Can you check the documentation and see if the defines in
drivers/pci/controller/dwc/pcie-designware.h still hold true?

Konrad