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From: Wolfram Sang <wsa@the-dreams.de>
To: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: linux-i2c@vger.kernel.org, linux-sh@vger.kernel.org,
	Magnus Damm <magnus.damm@gmail.com>,
	Simon Horman <horms@verge.net.au>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Kuninori Morimoto <kuninori.morimoto.gx@gmail.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	"linux-renesas-soc@vger.kernel.org"
	<linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v3 09/11] i2c: rcar: revoke START request early
Date: Thu, 31 Mar 2016 22:48:38 +0000	[thread overview]
Message-ID: <20160331224838.GA7381@katana> (raw)
In-Reply-To: <56FD9080.4090203@cogentembedded.com>

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On Fri, Apr 01, 2016 at 12:02:56AM +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 11/19/2015 06:56 PM, Wolfram Sang wrote:
> 
> >From: Wolfram Sang <wsa+renesas@sang-engineering.com>
> >
> >If we don't clear START generation as soon as possible, it may cause
> >another message to be generated, e.g. when receiving NACK in address
> >phase. To keep the race window as small as possible, we clear it right
> >at the beginning of the interrupt. We don't need any checks since we
> >always want to stop START and STOP generation on the next occasion after
> >we started it.
> >
> >This patch improves the situation but sadly does not completely fix it.
> >It is still to be researched if we can do better given this HW design.
> >
> >Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> 
>    Thanks for a great work, Wolfram!
>    We need this patch in -stable kernels. The R-Car audio just doesn't work
> without it...

Really only this patch? IIRC my tests showed that if you don't remove
the spinlocks (patch 4), the interrupt latency will already be too high
again. In any case, you'd need to do some careful backporting to rip
this out of the whole refactoring series. But maybe you did that already
and have good experiences?


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WARNING: multiple messages have this Message-ID (diff)
From: Wolfram Sang <wsa@the-dreams.de>
To: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: linux-i2c@vger.kernel.org, linux-sh@vger.kernel.org,
	Magnus Damm <magnus.damm@gmail.com>,
	Simon Horman <horms@verge.net.au>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Kuninori Morimoto <kuninori.morimoto.gx@gmail.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	"linux-renesas-soc@vger.kernel.org"
	<linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v3 09/11] i2c: rcar: revoke START request early
Date: Fri, 1 Apr 2016 00:48:38 +0200	[thread overview]
Message-ID: <20160331224838.GA7381@katana> (raw)
In-Reply-To: <56FD9080.4090203@cogentembedded.com>

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On Fri, Apr 01, 2016 at 12:02:56AM +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 11/19/2015 06:56 PM, Wolfram Sang wrote:
> 
> >From: Wolfram Sang <wsa+renesas@sang-engineering.com>
> >
> >If we don't clear START generation as soon as possible, it may cause
> >another message to be generated, e.g. when receiving NACK in address
> >phase. To keep the race window as small as possible, we clear it right
> >at the beginning of the interrupt. We don't need any checks since we
> >always want to stop START and STOP generation on the next occasion after
> >we started it.
> >
> >This patch improves the situation but sadly does not completely fix it.
> >It is still to be researched if we can do better given this HW design.
> >
> >Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> 
>    Thanks for a great work, Wolfram!
>    We need this patch in -stable kernels. The R-Car audio just doesn't work
> without it...

Really only this patch? IIRC my tests showed that if you don't remove
the spinlocks (patch 4), the interrupt latency will already be too high
again. In any case, you'd need to do some careful backporting to rip
this out of the whole refactoring series. But maybe you did that already
and have good experiences?


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  reply	other threads:[~2016-03-31 22:48 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-19 15:56 [PATCH v3 00/11] i2c: rcar: tackle race conditions in the driver Wolfram Sang
2015-11-19 15:56 ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 01/11] i2c: rcar: make sure clocks are on when doing clock calculation Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 02/11] i2c: rcar: rework hw init Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 03/11] i2c: rcar: remove unused IOERROR state Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 04/11] i2c: rcar: remove spinlock Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 05/11] i2c: rcar: refactor setup of a msg Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 06/11] i2c: rcar: init new messages in irq Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 07/11] i2c: rcar: don't issue stop when HW does it automatically Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 08/11] i2c: rcar: check master irqs before slave irqs Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 09/11] i2c: rcar: revoke START request early Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2016-03-31 21:02   ` Sergei Shtylyov
2016-03-31 21:02     ` Sergei Shtylyov
2016-03-31 22:48     ` Wolfram Sang [this message]
2016-03-31 22:48       ` Wolfram Sang
2016-04-01 19:55       ` Sergei Shtylyov
2016-04-01 19:55         ` Sergei Shtylyov
2016-04-01 20:14         ` Wolfram Sang
2016-04-01 20:14           ` Wolfram Sang
2016-04-01 23:05           ` Sergei Shtylyov
2016-04-01 23:05             ` Sergei Shtylyov
2016-04-02  7:27             ` Wolfram Sang
2016-04-02  7:27               ` Wolfram Sang
2016-04-02 12:51               ` Sergei Shtylyov
2016-04-02 12:51                 ` Sergei Shtylyov
2016-04-03  8:25                 ` Wolfram Sang
2016-04-03  8:25                   ` Wolfram Sang
2016-04-03 13:35                   ` Sergei Shtylyov
2016-04-03 13:35                     ` Sergei Shtylyov
2016-04-03 13:47                     ` Wolfram Sang
2016-04-03 13:47                       ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 10/11] i2c: rcar: clean up after refactoring Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 15:56 ` [PATCH v3 11/11] i2c: rcar: handle difference in setting up non-first message Wolfram Sang
2015-11-19 15:56   ` Wolfram Sang
2015-11-19 16:01 ` [PATCH v3 00/11] i2c: rcar: tackle race conditions in the driver Laurent Pinchart
2015-11-19 16:01   ` Laurent Pinchart
2015-11-30 13:27 ` Wolfram Sang
2015-11-30 13:27   ` Wolfram Sang

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