linux-kernel - Re: [PATCH] i2c: aspeed: Acknowledge most interrupts early in interrupt handler

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Date:   Tue, 18 Sep 2018 10:41:12 +0930
From:   Joel Stanley <joel@....id.au>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Andrew Jeffery <andrew@...id.au>, linux-i2c@...r.kernel.org,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        linux-aspeed@...ts.ozlabs.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Cédric Le Goater <clg@...d.org>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
Subject: Re: [PATCH] i2c: aspeed: Acknowledge most interrupts early in
 interrupt handler

On Fri, 14 Sep 2018 at 13:00, Guenter Roeck <linux@...ck-us.net> wrote:
>
> Commit 3e9efc3299dd ("i2c: aspeed: Handle master/slave combined irq events
> properly") moved interrupt acknowledgment to the end of the interrupt
> handler. In part this was done because the AST2500 datasheet says:
>
>  I2CD10 Interrupt Status Register
>    bit 2 Receive Done Interrupt status
>          S/W needs to clear this status bit to allow next data receiving.
>
> Acknowledging Receive Done before receive data was handled resulted in
> receive errors on high speed I2C busses.
>
> However, interrupt acknowledgment was not only moved to the end of the
> interrupt handler for Receive Done Interrupt status, but for all interrupt
> status bits. This could result in race conditions if a second interrupt was
> received during interrupt handling and not handled but still acknowledged
> at the end of the interrupt handler.
>
> Acknowledge only "Receive Done Interrupt status" late in the interrupt
> handler to solve the problem.
>
> Fixes: 3e9efc3299dd ("i2c: aspeed: Handle master/slave combined irq events properly")
> Cc: Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
> Cc: Joel Stanley <joel@....id.au>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>

Thanks for getting to the bottom of this Guenter. I gave it a spin on
Romulus (ast2500) and Palmetto (ast2400) without issue.

Tested-by: Joel Stanley <joel@....id.au>

Cheers,

Joel