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

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Message-ID: <bbc900f7-eb8f-2664-2144-50a9a6ad8453@quicinc.com>
Date: Wed, 16 Oct 2024 10:43:19 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@...aro.org>
CC: 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 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.

- Krishna Chaitanya.