linux-kernel - Re: [PATCH] arm64: dts: qcom: qcs6490-rb3gen2: Add PCIe nodes

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Message-ID: <CAA8EJppbY+YCesE4R4zV83CpCryyZNzvuzoNpgk+8a8h7mCzqw@mail.gmail.com>
Date: Tue, 22 Oct 2024 20:22:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, quic_vbadigan@...cinc.com, 
	quic_ramkri@...cinc.com, quic_nitegupt@...cinc.com, quic_skananth@...cinc.com, 
	quic_parass@...cinc.com
Subject: Re: [PATCH] arm64: dts: qcom: qcs6490-rb3gen2: Add PCIe nodes

On Tue, 22 Oct 2024 at 18:10, Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
>
> On Thu, Oct 17, 2024 at 02:12:00PM +0300, Dmitry Baryshkov wrote:
> > On Wed, Oct 16, 2024 at 10:43:19AM +0530, Krishna Chaitanya Chundru wrote:
> > >
> > >
> > > On 10/14/2024 4:55 AM, Dmitry Baryshkov wrote:
> > > > On Sat, Oct 12, 2024 at 06:13:34PM +0530, Manivannan Sadhasivam wrote:
> > > > > On Fri, Oct 11, 2024 at 05:24:29PM +0530, Krishna Chaitanya Chundru wrote:
> > > > >
> > > > > [...]
> > > > >
> > > > > > > > The logic here is that the fixed endpoints in the switch will get an unique SID
> > > > > > > > and the devices getting attached to slots will share the same SID of the bus
> > > > > > > > (this is the usual case with all Qcom SoCs).
> > > > > > > >
> > > > > > > > But I guess we would need 'iommu-map-mask' as well. Hope this addresses your
> > > > > > > > concern.
> > > > > > >
> > > > > > > Yes, thank you!
> > > > > > >
> > > > > > Hi dimitry & mani,
> > > > > >
> > > > > > This particular board variant doesn't expose any open slots to connect
> > > > > > a different endpoints like another switch(which might have BDF unknown
> > > > > > to us) so static table should be fine for this board variant.
> > > > > >
> > > > > > I tries to add iommu-map-mask property, the issue with that property is
> > > > > > that the driver is applying the mask to the bdf before searching for the
> > > > > > entry in the table. If I use a mask value which satisfies all the
> > > > > > entries in the table ( mask as 0x718) and if a new bdf is enumerated
> > > > > > lets say 0x600 due to mask 0x718 its value is again 0x600 only.
> > > > > >
> > > > > > Can we skip iommu-map-mask property and use only static table for this
> > > > > > board as we know this board doesn't expose any open slots.
> > > > > >
> > > > >
> > > > > Hmm, I was not aware that it doesn't have open slots. Fine with me then.
> > > >
> > > > It doesn't feature open slots, but it has two PCIe connections on HS2 /
> > > > HS3. Users might attach external PCIe devices.
> > > >
> > > > Krishna, could you please clarify, how those two connections are routed?
> > > >
> > > For this qps615 board to one of the downstream port (pcie to usb) usb
> > > hub is connected and to the other downstream port NVMe will be
> > > connected.
> >
> > The board has two PCIe links routed to the HS2 and HS3 connectors. Are
> > they routed to the PCIe switch?
> >
> > Yes, they are not standard slots, but still the board is expandable and
> > it is possible to connect external PCIe devices. As such it is not
> > possible to have static SID mapping.
> >
>
> Sorry, I think the conversation got deviated. We have concluded that the
> endpoints fixed (soldered) in the board will get a fixed SID (because we know
> what they are) and all other devices going to get connected to HS/LS connectors
> will get shared SID (because we don't know what they are).
>
> Any concern with that?

This is perfectly fine with me.

-- 
With best wishes
Dmitry