linux-kernel - Re: [PATCH v2] w1: masters: omap_hdq: Add support for 1-wire mode

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Date:	Fri, 12 Jun 2015 10:53:35 +0530
From:	Vignesh R <vigneshr@...com>
To:	Evgeniy Polyakov <zbr@...emap.net>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	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>
CC:	Tony Lindgren <tony@...mide.com>, NeilBrown <neilb@...e.de>,
	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 v2] w1: masters: omap_hdq: Add support for 1-wire mode

Hi,

On Thursday 11 June 2015 09:04 PM, Evgeniy Polyakov wrote:
> Hi
> 
> 25.05.2015, 08:15, "Vignesh R" <vigneshr@...com>:
>>>  HDQ mode remains unchanged.
>>>
>>>  Signed-off-by: Vignesh R <vigneshr@...com>
> 
> I have no experience with omap_hdq platform, but there are quite a few questions
> related to IO - you never check whether write was successful or read returned actually
> valid data, is it ok? I mean is it correct to assume that read can not return 0xff for example
> and it is a sign that something is wrong, or this can not happen?
> 

Referring to AM437x TRM SPRUHL7C
(www.ti.com/lit/ug/spruhl7c/spruhl7c.pdf) section 23.3.5.4, Successful
or failed completion is not indicated for write operation, so there is
no way to verify whether write succeeded (though TX_COMPLETE interrupt
bit is set on transaction completion). But, as for as read operation is
concerned, the TRM says, if RX_COMPLETE bit is set, then read is
successful and I think that implies valid data is present in RX reg. My
patch does look for TX/RX_COMPLETE bits to be set after write/read
operations.

> As for me, I have no objection, but this patch must go via omap tree imo.
> 

Andrew Morton has already picked this patch (its on linux-next).
Although he has a minor comment on use of mutex_lock_interruptible. But
that comment applies to many places in the existing driver code. I plan
to cleanup all those mutex calls in near future.

Regards
Vignesh
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