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

From: Johan Hovold <johan@kernel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: "Krzysztof Kozlowski" <krzysztof.kozlowski@linaro.org>,
	"Johan Hovold" <johan+linaro@kernel.org>,
	"Bjorn Andersson" <andersson@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Konrad Dybcio" <konrad.dybcio@linaro.org>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	linux-arm-msm@vger.kernel.org, linux-pci@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/10] dt-bindings: PCI: qcom: Do not require 'msi-map-mask'
Date: Tue, 20 Feb 2024 09:42:17 +0100	[thread overview]
Message-ID: <ZdRl6fzEOQqkXqLt@hovoldconsulting.com> (raw)
In-Reply-To: <ZdRXpQnbDbojlMkV@hovoldconsulting.com>

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