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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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.

Looks very nice, great job!

Only one minor comment, and you can just send a follow-up patch for it:

> +	/* prepare data pushed out to devices in buf[0..setbuf_len) */
> +	list_for_each_entry(sdevice, &smaster->devices, node) {
> +		struct siox_driver *sdriver =
> +			to_siox_driver(sdevice->dev.driver);
> +		sdevice->status_written = smaster->status;
> +
> +		i -= sdevice->inbytes;
> +
> +		/*
> +		 * If the device or a previous one is unsynced, don't pet the
> +		 * watchdog. This is done to ensure that the device is kept in
> +		 * reset when something is wrong.
> +		 */
> +		if (!siox_device_synced(sdevice))
> +			unsync_error = 1;
> +
> +		if (sdriver && !unsync_error)
> +			sdriver->set_data(sdevice, sdevice->status_written,
> +					  &smaster->buf[i + 1]);
> +		else
> +			/*
> +			 * Don't trigger watchdog if there is no driver or a
> +			 * sync problem
> +			 */
> +			sdevice->status_written &= ~SIOX_STATUS_WDG;
> +
> +		smaster->buf[i] = sdevice->status_written;
> +	}
> +
> +	WARN_ON(i);

What can someone do if this WARN_ON() triggers?  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.

thanks,

greg k-h