From mboxrd@z Thu Jan 1 00:00:00 1970 From: swarren@wwwdotorg.org (Stephen Warren) Date: Tue, 26 Jul 2016 10:21:56 -0600 Subject: [PATCH 2/3] dt-bindings: allow child nodes inside the Tegra BPMP In-Reply-To: <20160726100302.GE2433@ulmo.ba.sec> References: <20160719191442.15439-1-swarren@wwwdotorg.org> <20160719191442.15439-2-swarren@wwwdotorg.org> <20160726100302.GE2433@ulmo.ba.sec> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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:-(