linux-kernel - Re: [PATCH v2 7/8] PCI: qcom: Add support for host_stop_link() & host_start

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Message-ID: <ar63lbc5nl6jujeadd4srfd2dacsjk7la5kzma24bi2cqb7awj@vfawrbnr7an4>
Date: Mon, 2 Sep 2024 21:32:39 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc: Bjorn Helgaas <helgaas@...nel.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, cros-qcom-dts-watchers@...omium.org, 
	Bartosz Golaszewski <brgl@...ev.pl>, Jingoo Han <jingoohan1@...il.com>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, andersson@...nel.org, quic_vbadigan@...cinc.com, 
	linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 7/8] PCI: qcom: Add support for host_stop_link() &
 host_start_link()

On Mon, Sep 02, 2024 at 12:21:22PM GMT, Krishna Chaitanya Chundru wrote:
> 
> 
> On 8/7/2024 12:42 AM, Bjorn Helgaas wrote:
> > On Sat, Aug 03, 2024 at 08:52:53AM +0530, Krishna chaitanya chundru wrote:
> > > For the switches like QPS615 which needs to configure it before
> > > the PCIe link is established.
> > > 
> > > if the link is not up assert the PERST# and disable LTSSM bit so
> > > that PCIe controller will not participate in the link training
> > > as part of host_stop_link().
> > > 
> > > De-assert the PERST# and enable LTSSM bit back in host_start_link().
> > > 
> > > Introduce ltssm_disable function op to stop the link training.
> > 
> > pcie-qcom.c is a driver for a PCIe host controller.  Apparently QPS615
> > is a switch in a hierarchy that could be below any PCIe host
> > controller, so I'm missing the connection with pcie-qcom.c.
> > 
> > Does this fix a problem that only occurs with pcie-qcom.c?  What
> > happens if you put a QPS615 below some other controller?
> > 
> Hi Bjorn,
> 
> The qps615 is the qualcomm in-house PCIe switch it is not available to
> others. so we are trying to add for qualcomm soc's only.

Any guarantee that the status quo will stay so in future? Or that it
won't appear on Qualcomm platform with the virtualized PCIe controller?

-- 
With best wishes
Dmitry