linux-kernel - Re: [PATCH v4 4/8] of: property: Add fw_devlink support for optional properties

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Message-ID: <20210209213320.GA219007@robh.at.kernel.org>
Date:   Tue, 9 Feb 2021 15:33:20 -0600
From:   Rob Herring <robh@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Len Brown <lenb@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH v4 4/8] of: property: Add fw_devlink support for optional
 properties

On Fri, Feb 05, 2021 at 02:26:40PM -0800, Saravana Kannan wrote:
> Not all DT bindings are mandatory bindings. Add support for optional DT
> bindings and mark iommus, iommu-map, dmas as optional DT bindings.

I don't think we can say these are optional or not. It's got to be a 
driver decision somehow.

For example, if IOMMU is optional, what happens with this sequence:

driver probes without IOMMU
driver calls dma_map_?()
IOMMU driver probes
h/w accesses DMA buffer --> BOOM!