From mboxrd@z Thu Jan 1 00:00:00 1970 From: swarren@wwwdotorg.org (Stephen Warren) Date: Wed, 27 Jul 2016 15:50:52 -0600 Subject: [PATCH 2/3] dt-bindings: allow child nodes inside the Tegra BPMP In-Reply-To: References: <20160719191442.15439-1-swarren@wwwdotorg.org> <20160719191442.15439-2-swarren@wwwdotorg.org> <20160726100302.GE2433@ulmo.ba.sec> Message-ID: <36967d69-cb2a-654e-9a4c-2021fd476464@wwwdotorg.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/26/2016 10:21 AM, Stephen Warren wrote: > On 07/26/2016 04:03 AM, Thierry Reding wrote: >> On Tue, Jul 19, 2016 at 01:14:41PM -0600, Stephen Warren wrote: >>> From: Stephen Warren >>> >>> The BPMP implements some services which must be represented by separate >>> nodes. For example, it can provide access to certain I2C controllers, >>> and >>> the I2C bindings represent each I2C controller as a device tree node. >>> Update the binding to describe how the BPMP supports this. >>> >>> Signed-off-by: Stephen Warren >>> --- >>> .../bindings/firmware/nvidia,tegra186-bpmp.txt | 23 >>> ++++++++++++++++++++++ >>> 1 file changed, 23 insertions(+) >>> >>> diff --git >>> a/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt >>> b/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt >>> index 9a3864f56955..142d363406f6 100644 >>> --- >>> a/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt >>> +++ >>> b/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt >>> @@ -38,6 +38,24 @@ implemented by this node: >>> - .../reset/reset.txt >>> - >>> >>> +The BPMP implements some services which must be represented by >>> separate nodes. >>> +For example, it can provide access to certain I2C controllers, and >>> the I2C >>> +bindings represent each I2C controller as a device tree node. Such >>> nodes should >>> +be nested directly inside the main BPMP node. >>> + >>> +Software can determine whether a child node of the BPMP node >>> represents a device >>> +by checking for a compatible property. Any node with a compatible >>> property >>> +represents a device that can be instantiated. Nodes without a >>> compatible >>> +property may be used to provide configuration information regarding >>> the BPMP >>> +itself, although no such configuration nodes are currently defined >>> by this >>> +binding. >>> + >>> +The BPMP firmware defines no single global name-/numbering-space for >>> such >>> +services. Put another way, the numbering scheme for I2C buses is >>> distinct from >>> +the numbering scheme for any other service the BPMP may provide >>> (e.g. a future >>> +hypothetical SPI bus service). As such, child device nodes will have >>> no reg >>> +property, and the BPMP node will have no #address-cells or >>> #size-cells property. >> >> My understanding is that the I2C bus number is passed as part of the >> request to the BPMP firmware. Does that not count as addressing? Could >> we not represent that generically using a device tree hierarchy? I'm >> thinking something along these lines: >> >> bpmp { >> ... >> >> services { >> i2c { >> i2c at 0 { >> reg = <0>; > > Technically, that is possible. However, Rob Herring rejected the idea of > multiple levels of sub-nodes. > > Can we please just go with what we have? DT bindings are frankly an > obstacle to getting anything done:-( Thierry, any further thoughts here? I really need to get these DT bindings finalized so that I can use them in U-Boot, which is very urgent. Thanks.