linux-kernel - Re: [PATCH] i2c: aspeed: Add multi-master use case support

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Date:   Fri, 8 Feb 2019 22:48:49 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, linux-i2c@...r.kernel.org,
        openbmc@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        James Feist <james.feist@...ux.intel.com>,
        Vernon Mauery <vernon.mauery@...ux.intel.com>
Subject: Re: [PATCH] i2c: aspeed: Add multi-master use case support

On Wed, Jan 16, 2019 at 11:39:58AM -0800, Jae Hyun Yoo wrote:
> In multi-master environment, this driver's master cannot know
> exactly when a peer master sends data to this driver's slave so
> cases can be happened that this master tries sending data through
> the master_xfer function but slave data from a peer master is still
> being processed or slave xfer is started by a peer immediately
> after it queues a master command. To support multi-master use cases
> properly, this H/W provides arbitration in physical level and it
> provides priority based command handling too to avoid conflicts in
> multi-master environment, means that if a master and a slave events
> happen at the same time, H/W will handle a higher priority event
> first and a pending event will be handled when bus comes back to
> the idle state.
> 
> To support this H/W feature properly, this patch adds the 'pending'
> state of master and its handling code so that the pending master
> xfer can be continued after slave operation properly.
> 
> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>

Hmmm, the #ifdeffery quite increases with this patch. Maybe it is easier
to select I2C_SLAVE in Kconfig? I'll let you decide.

My code checkers found this:

    CPPCHECK
drivers/i2c/busses/i2c-aspeed.c:694:10: warning: Variable 'ret' is assigned a value that is never used. [unreadVariable]


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