linux-kernel - Re: [PATCH 2/3] i2c: slave-mqueue: add a slave backend to receive and queue messages

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Message-ID: <20190605143158.GB1534@u40b0340c692b58f6553c.ant.amazon.com>
Date:   Wed, 5 Jun 2019 07:31:58 -0700
From:   Eduardo Valentin <eduval@...zon.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Eduardo Valentin <eduval@...zon.com>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Haiyue Wang <haiyue.wang@...ux.intel.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] i2c: slave-mqueue: add a slave backend to receive
 and queue messages

On Wed, Jun 05, 2019 at 11:25:39AM +0300, Andy Shevchenko wrote:
> On Wed, Jun 5, 2019 at 6:30 AM Eduardo Valentin <eduval@...zon.com> wrote:
> >
> > Hey Andry,
> >
> > Long time no seeing :-)
> 
> True!
> 
> 
> > > > +#define MQ_MSGBUF_SIZE             CONFIG_I2C_SLAVE_MQUEUE_MESSAGE_SIZE
> > > > +#define MQ_QUEUE_SIZE              CONFIG_I2C_SLAVE_MQUEUE_QUEUE_SIZE
> > >
> > > > +#define MQ_QUEUE_NEXT(x)   (((x) + 1) & (MQ_QUEUE_SIZE - 1))
> > >
> > > Also possible ((x + 1) % ..._SIZE)
> >
> > Right.. but I suppose the original idea is to avoid divisions on the hotpath.
> >
> > So, I am actually fine with the limitation of only using power of 2.
> 
> The original code implies that anyway, so, my proposal doesn't
> restrict it any farther.

Well, yes, but the point is you would be switching from a simple AND (&) operation
to a division...

I am keeping the power of 2 dep so that we can keep this with a simple &.

> > > > +   {
> > > > +           .compatible = "i2c-slave-mqueue",
> > > > +   },
> > >
> > > > +   { },
> > >
> > > No need for comma here.
> >
> > It does not hurt to have it either :-)
> 
> It's just a protection against some weird cases of adding entries
> behind the terminator.

Fair..

> 
> > > > +           .of_match_table = of_match_ptr(i2c_slave_mqueue_of_match),
> > >
> > > Wouldn't compiler warn you due to unused data?
> > > Perhaps drop of_match_ptr() for good...
> >
> >
> > Not sure what you meant here. I dont see any compiler warning.
> > Also, of_match_ptr seams to be well spread in the kernel.
> 
> If this will be compiled with CONFIG_OF=n...

I see.. I obviously did not test with that config..

> Though I didn't check all dependencies to see if it even possible. In
> any case of_match_ptr() is redundant in both cases here.
> Either you need to protect i2c_slave_mqueue_of_match with #ifdef
> CONFIG_OF, or drop the macro use.

I will wrap it into CONFIG_OF..

> 
> P.S. Taking into account the last part, I would wait for v7 with that
> fixed followed by fixing other nits.

I agree, the warn on CONFIG_OF=n is enough to spin out an extra version.
I will include the other nits too.

> 
> -- 
> With Best Regards,
> Andy Shevchenko

-- 
All the best,
Eduardo Valentin