linux-kernel - Re: [PATCH v1 1/5] siox: new driver framework for eckelmann SIOX

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Message-ID: <20171218154421.k7bqzbjx2rqkl6e4@pengutronix.de>
Date:   Mon, 18 Dec 2017 16:44:21 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Gavin Schenk <g.schenk@...elmann.de>
Subject: Re: [PATCH v1 1/5] siox: new driver framework for eckelmann SIOX

Hello Greg,

thanks for your feedback.

On Mon, Dec 18, 2017 at 04:08:33PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 07, 2017 at 10:30:04AM +0100, Uwe Kleine-König wrote:
> > SIOX is a bus system invented at Eckelmann AG to control their building
> > management and refrigeration systems. Traditionally the bus was
> > implemented on custom microcontrollers, today Linux based machines are
> > in use, too.
> > 
> > The topology on a SIOX bus looks as follows:
> > 
> >       ,------->--DCLK-->---------------+----------------------.
> >       ^                                v                      v
> >  ,--------.                ,----------------------.       ,------
> >  |        |                |   ,--------------.   |       |
> >  |        |--->--DOUT-->---|->-|shift register|->-|--->---|
> >  |        |                |   `--------------'   |       |
> >  | master |                |        device        |       |  device
> >  |        |                |   ,--------------.   |       |
> >  |        |---<--DIN---<---|-<-|shift register|-<-|---<---|
> >  |        |                |   `--------------'   |       |
> >  `--------'                `----------------------'       `------
> >       v                                ^                      ^
> >       `----------DLD-------------------+----------------------'
> > 
> > There are two control lines (DCLK and DLD) driven from the bus master to
> > all devices in parallel and two daisy chained data lines, one for input
> > and one for output. DCLK is the clock to shift both chains by a single
> > bit. On an edge of DLD the devices latch both their input and output
> > shift registers.
> > 
> > This patch adds a framework for this bus type.
> 
> Oops, you forgot a Documentation/ABI/ patch for all of the new sysfs
> files you are creating here.

Will look into what is already there and come up with something similar.

> Also, why use kernfs direct nodes?  That feels "odd" to me.

What is the better alternative?

In another mail Greg Kroah-Hartman wrote:
> Looks very nice, great job!

\o/

> Only one minor comment, and you can just send a follow-up patch for
> it:
> 
> > +   WARN_ON(i);
> 
> What can someone do if this WARN_ON() triggers?

I would expect this to be reported to Gavin and me.

> Seems like it is left-over debugging code?  If not, make it a "real"
> error and handle it properly.  Or provide some sort of context as to
> what is going on here.

Well, during development it was a BUG_ON :-) I will think for v2 about
how this can be better handled or drop it.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |