linux-kernel - Re: [PATCH 02/10] dt-bindings: PCI: qcom: Do not require 'msi-map-mask'

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Date: Tue, 20 Feb 2024 08:41:25 +0100
From: Johan Hovold <johan@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] dt-bindings: PCI: qcom: Do not require
 'msi-map-mask'

On Fri, Feb 16, 2024 at 10:24:06PM +0530, Manivannan Sadhasivam wrote:
> On Wed, Feb 14, 2024 at 02:38:57PM +0100, Krzysztof Kozlowski wrote:
> > On 14/02/2024 13:54, Johan Hovold wrote:
> > > On Wed, Feb 14, 2024 at 01:01:20PM +0100, Krzysztof Kozlowski wrote:
> > >> On 12/02/2024 17:50, Johan Hovold wrote:
> > >>> Whether the 'msi-map-mask' property is needed or not depends on how the
> > >>> MSI interrupts are mapped and it should therefore not be described as
> > >>> required.
> > >>
> > >> I could imagine that on all devices the interrupts are mapped in a way
> > >> you need to provide msi-map-mask. IOW, can there be a Qualcomm platform
> > >> without msi-map-mask?
> > > 
> > > I don't have access to the documentation so I'll leave that for you guys
> > > to determine. I do note that the downstream DT does not use it and that
> > > we have a new devicetree in linux-next which also does not have it:
> > > 
> > > 	https://lore.kernel.org/r/20240125-topic-sm8650-upstream-pcie-its-v1-1-cb506deeb43e@linaro.org
> > > 
> > > But at least the latter looks like an omission that should be fixed.
> > 
> > Hm, either that or the mask for sm8450 was not needed as well. Anyway,
> > thanks for explanation, appreciated!
> 
> msi-map-mask is definitely needed as it would allow all the devices under the
> same bus to reuse the MSI identifier. Currently, excluding this property will
> not cause any issue since there is a single device under each bus. But we cannot
> assume that is going to be the case on all boards.

Are you saying that there is never a use case for an identity mapping?
Just on Qualcomm hardware or in general?

It looks like we have a fairly large number of mainline devicetrees that
do use an identity mapping here (i.e. do not specify 'msi-map-mask') and
the binding document also has an explicit example of this.

	Documentation/devicetree/bindings/pci/pci-msi.txt

> I will submit a patch to fix SM8650.

Johan