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

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Message-ID: <ZdRl6fzEOQqkXqLt@hovoldconsulting.com>
Date: Tue, 20 Feb 2024 09:42:17 +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 Tue, Feb 20, 2024 at 08:41:25AM +0100, Johan Hovold wrote:
> On Fri, Feb 16, 2024 at 10:24:06PM +0530, Manivannan Sadhasivam wrote:

> > 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

The above should have said "linear mapping" as the msi-base is not
always identical to the rid-base, but you get the point.

Johan