linux-kernel - Re: [PATCH RESEND] w1: masters: omap

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Date:	Fri, 15 May 2015 17:35:02 +0530
From:	Vignesh R <vigneshr@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Evgeniy Polyakov <zbr@...emap.net>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jonathan Corbet <corbet@....net>, NeilBrown <neilb@...e.de>,
	Tony Lindgren <tony@...mide.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Fabian Frederick <fabf@...net.be>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH RESEND] w1: masters: omap_hdq: Add support for 1-wire
 mode


On Thursday 14 May 2015 02:19 AM, Andrew Morton wrote:
> On Mon, 4 May 2015 14:08:55 +0530 Vignesh R <vigneshr@...com> wrote:
> 
>> This patches makes following changes to omap_hdq driver
>>  - Enable 1-wire mode.
>>  - Implement w1_triplet callback to facilitate search rom
>>    procedure and auto detection of 1-wire slaves.
>>  - Proper enabling and disabling of interrupt.
>>  - Cleanups (formatting and return value checks).
>>
>> HDQ mode remains unchanged.
>>
>> ...
>>
>> +/*
>> + * W1 triplet callback function - used for searching ROM addresses.
>> + * Registered only when controller is in 1-wire mode.
>> + */
>> +static u8 omap_w1_triplet(void *_hdq, u8 bdir)
>> +{
>> +	u8 ret, id_bit, comp_bit;
>> +	struct hdq_data *hdq_data = _hdq;
>> +	u8 ctrl = OMAP_HDQ_CTRL_STATUS_SINGLE | OMAP_HDQ_CTRL_STATUS_GO |
>> +		  OMAP_HDQ_CTRL_STATUS_INTERRUPTMASK;
>> +	u8 mask = ctrl | OMAP_HDQ_CTRL_STATUS_DIR;
>> +
>> +	omap_hdq_get(_hdq);
>> +
>> +	ret = mutex_lock_interruptible(&hdq_data->hdq_mutex);
>> +	if (ret < 0) {
>> +		ret = -EINTR;
>> +		goto rtn;
> 
> Has this code path been tested?  What happens when it is taken?  Driver
> initialization fails?  If so, why is this desirable behaviour?

The w1 core code that calls omap_w1_triplet (w1_triplet from w1_io.c)
doesn't care about error codes returned by omap_w1_triplet. Hence, I
will add a debug print and return 0x3 indicating to the w1 core to start
the search again.

> 
>> +	}
>> +
>> +	hdq_data->hdq_irqstatus = 0;
>> +	/* read id_bit */
>> +	hdq_reg_merge(_hdq, OMAP_HDQ_CTRL_STATUS,
>> +		      ctrl | OMAP_HDQ_CTRL_STATUS_DIR, mask);
>> +	wait_event_timeout(hdq_wait_queue,
>> +			   (hdq_data->hdq_irqstatus
>> +			   & OMAP_HDQ_INT_STATUS_RXCOMPLETE),
>> +			   OMAP_HDQ_TIMEOUT);
> 
> It seems bad to ignore a timeout.  Shouldn't the code clean up and
> report error when this occurs?
> 
> 
>> +	id_bit = (hdq_reg_in(_hdq, OMAP_HDQ_RX_DATA) & 0x01);
>> +
>> +	hdq_data->hdq_irqstatus = 0;
>> +	/* read comp_bit */
>> +	hdq_reg_merge(_hdq, OMAP_HDQ_CTRL_STATUS,
>> +		      ctrl | OMAP_HDQ_CTRL_STATUS_DIR, mask);
>> +	wait_event_timeout(hdq_wait_queue,
>> +			   (hdq_data->hdq_irqstatus
>> +			   & OMAP_HDQ_INT_STATUS_RXCOMPLETE),
>> +			   OMAP_HDQ_TIMEOUT);
> 
> Here too.
> 
>> +	comp_bit = (hdq_reg_in(_hdq, OMAP_HDQ_RX_DATA) & 0x01);
>> +
>> +	if (id_bit && comp_bit) {
>> +		ret = 0x03;  /* error */
>> +		goto rtn;
>> +	}
>> +	if (!id_bit && !comp_bit) {
>> +		/* Both bits are valid, take the direction given */
>> +		ret = bdir ? 0x04 : 0;
>> +	} else {
>> +		/* Only one bit is valid, take that direction */
>> +		bdir = id_bit;
>> +		ret = id_bit ? 0x05 : 0x02;
>> +	}
>> +
>> +	/* write bdir bit */
>> +	hdq_reg_out(_hdq, OMAP_HDQ_TX_DATA, bdir);
>> +	hdq_reg_merge(_hdq, OMAP_HDQ_CTRL_STATUS, ctrl, mask);
>> +	wait_event_timeout(hdq_wait_queue,
>> +			   (hdq_data->hdq_irqstatus
>> +			   & OMAP_HDQ_INT_STATUS_TXCOMPLETE),
>> +			   OMAP_HDQ_TIMEOUT);
> 
> And here.

I will add a dev_dbg() and return 0x3 indicating no devices responded in
all the above cases.

> 
>> +	hdq_reg_merge(_hdq, OMAP_HDQ_CTRL_STATUS, 0,
>> +		      OMAP_HDQ_CTRL_STATUS_SINGLE);
>> +
>> +rtn:
>> +	mutex_unlock(&hdq_data->hdq_mutex);
>> +	omap_hdq_put(_hdq);
>> +	return ret;
>> +}
>>
>> ...
>>

Thanks & Regards
Vignesh
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