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

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Message-ID: <7yzjgqitjvfwricftcpelktwjbgwkjuibwkpodjd6x4gwkjkw3@wkeqp6lqwfqv>
Date: Mon, 14 Oct 2024 02:25:30 +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 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?

-- 
With best wishes
Dmitry