linux-kernel - Re: [PATCH v7 00/12] mux controller abstraction and iio/i2c muxes

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Message-ID: <20170108105129.GB1983@katana>
Date:   Sun, 8 Jan 2017 11:51:29 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v7 00/12] mux controller abstraction and iio/i2c muxes

Hi peda,

> One thing that I would like to do, but don't see a solution
> for, is to move the mux control code that is present in
> various drivers in drivers/i2c/muxes to this new minimalistic
> muxing subsystem, thus converting all present i2c muxes (but
> perhaps not gates and arbitrators) to be i2c-mux-simple muxes.

In a few lines, what is preventing that?

> I'm using an rwsem to lock a mux, but that isn't really a
> perfect fit. Is there a better locking primitive that I don't
> know about that fits better? I had a mutex at one point, but
> that didn't allow any concurrent accesses at all. At least
> the rwsem allows concurrent access as long as all users
> agree on the mux state, but I suspect that the rwsem will
> degrade to the mutex situation pretty quickly if there is
> any contention.

Maybe ask this question in a seperate email thread on lkml cc-ing the
locking gurus (with a pointer to this thread)?

> Also, the "mux" name feels a bit ambitious, there are many muxes
> in the world, and this tiny bit of code is probably not good
> enough to be a nice fit for all...

"... and it probably never will support anything other than
AT-harddisks, as that's all I have..." ;))

Thanks for this work!

   Wolfram


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