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

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Date:	Mon, 18 Jul 2016 12:29:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"H. Nikolaus Schaller" <hns@...delico.com>
Cc:	Evgeniy Polyakov <zbr@...emap.net>, Vignesh R <vigneshr@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andreas Kemnade <andreas@...nade.info>,
	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>,
	Tony Lindgren <tony@...mide.com>, NeilBrown <neilb@...e.de>,
	Fabian Frederick <fabf@...net.be>,
	linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org
Subject: Re: [PATCH] w1:omap_hdq: fix regression

On Mon, 18 Jul 2016 18:10:37 +0200 "H. Nikolaus Schaller" <hns@...delico.com> wrote:

> commit <e93762bbf681> ("w1: masters: omap_hdq: add support for 1-wire mode")
> did add a statement to clear the hdq_irqstatus flags in hdq_read_byte().
> 
> If the hdq reading process is scheduled slowly or interrupts are disabled
> for a while the hardware read activity might already be finished on entry
> of hdq_read_byte(). And hdq_isr() already has set the hdq_irqstatus to
> 0x6 (can be seen in debug mode) denoting that both, the TXCOMPLETE
> and RXCOMPLETE interrupts occurred in parallel.
> 
> This means there is no need to wait and the hdq_read_byte() can just read
> the byte from the hdq controller.
> 
> By resetting hdq_irqstatus to 0 the read process is forced to be always
> waiting again (because the if statement always succeeds) but the hardware
> will not issue another RXCOMPLETE interrupt. This results in a false
> timeout.
> 
> After such a situation the hdq bus hangs.
> 
> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>

Needs a cc:stable.

I'll assume Greg will be handling this patch.