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 15:45:06 +0300
From: Abel Vesa <abel.vesa@...aro.org>
To: Konrad Dybcio <konrad.dybcio@...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 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.

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

> 
> Konrad
> 
> [1] https://lore.kernel.org/all/Zl8H0KOrfuF91kpZ@linaro.org/