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

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Message-ID: <qevhitaa47fd77jrrs4viv6mctkhedoz5jy33ruqvv62qrb44y@owzfxnxrapvf>
Date: Thu, 17 Oct 2024 14:12:00 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	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 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.

-- 
With best wishes
Dmitry