linux-kernel - Re: [PATCH v0 linux master] i2c/busses: Avoid i2c interrupt status clear race condition.

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Message-ID: <20200429075357.GA1957@kunai>
Date:   Wed, 29 Apr 2020 09:53:57 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     ryan_chen <ryan_chen@...eedtech.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, linux-i2c@...r.kernel.org,
        openbmc@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v0 linux master] i2c/busses: Avoid i2c interrupt status
 clear race condition.

On Wed, Apr 29, 2020 at 11:37:37AM +0800, ryan_chen wrote:
> In AST2600 there have a slow peripheral bus between CPU
>  and i2c controller.
> Therefore GIC i2c interrupt status clear have delay timing,
> when CPU issue write clear i2c controller interrupt status.
> To avoid this issue, the driver need have read after write
>  clear at i2c ISR.
> 
> Signed-off-by: ryan_chen <ryan_chen@...eedtech.com>

v0? is it a prototype?

And is there maybe a Fixes: tag for it?

> ---
>  drivers/i2c/busses/i2c-aspeed.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index 07c1993274c5..f51702d86a90 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -603,6 +603,7 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
>  	/* Ack all interrupts except for Rx done */
>  	writel(irq_received & ~ASPEED_I2CD_INTR_RX_DONE,
>  	       bus->base + ASPEED_I2C_INTR_STS_REG);
> +	readl(bus->base + ASPEED_I2C_INTR_STS_REG);
>  	irq_remaining = irq_received;
>  
>  #if IS_ENABLED(CONFIG_I2C_SLAVE)
> @@ -645,9 +646,11 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
>  			irq_received, irq_handled);
>  
>  	/* Ack Rx done */
> -	if (irq_received & ASPEED_I2CD_INTR_RX_DONE)
> +	if (irq_received & ASPEED_I2CD_INTR_RX_DONE) {
>  		writel(ASPEED_I2CD_INTR_RX_DONE,
>  		       bus->base + ASPEED_I2C_INTR_STS_REG);
> +		readl(bus->base + ASPEED_I2C_INTR_STS_REG);
> +	}
>  	spin_unlock(&bus->lock);
>  	return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
>  }
> -- 
> 2.17.1
> 

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