linux-kernel - [PATCH] i2c: mux: Add more warnings to i2c-arb-gpio-challenge docs

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Message-Id: <1398792651-27115-1-git-send-email-dianders@chromium.org>
Date:	Tue, 29 Apr 2014 10:30:51 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	olof@...om.net, Doug Anderson <dianders@...omium.org>,
	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	rdunlap@...radead.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] i2c: mux: Add more warnings to i2c-arb-gpio-challenge docs

This adds some more warnings to the i2c-arb-gpio-challenge docs to
help encourage people not to use it in their designs unless they have
no choice.

Signed-off-by: Doug Anderson <dianders@...omium.org>
---
 Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
index 1ac8ea8..bfeabb8 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
@@ -8,6 +8,12 @@ the standard I2C multi-master rules.  Using GPIOs is generally useful in
 the case where there is a device on the bus that has errata and/or bugs
 that makes standard multimaster mode not feasible.
 
+Note that this scheme works well enough but has some downsides:
+* It is nonstandard (not using standard I2C multimaster)
+* Having two masters on a bus in general makes it relatively hard to debug
+  problems (hard to tell if i2c issues were caused by one master, another, or
+  some device on the bus).
+
 
 Algorithm:
 
-- 
1.9.1.423.g4596e3a

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