linux-kernel - Re: [PATCH 1/1] I2C: designware: fix IO timeout issue for AMD controller

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Date:	Thu, 5 Nov 2015 15:52:16 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Xiangliang Yu <Xiangliang.Yu@....com>
Cc:	andriy.shevchenko@...ux.intel.com, jarkko.nikula@...ux.intel.com,
	wsa@...-dreams.de, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Ken.Xue@....com, Vincent.Wan@....com,
	Ray.Huang@....com, Annie.Wang@....com, Tony.Li@....com
Subject: Re: [PATCH 1/1] I2C: designware: fix IO timeout issue for AMD
 controller

On Thu, Nov 05, 2015 at 08:34:44PM +0800, Xiangliang Yu wrote:
> Because of some hardware limitation, AMD I2C controller can't
> trigger next interrupt if interrupt status has been changed
> after clearing interrupt status bits. Then, I2C will lost
> interrupt and IO timeout.
> 
> According to hardware design, this patch implements a workaround
> to disable i2c controller interrupt after clearing interrupt bits
> when entering ISR and to enable i2c interrupt before exiting ISR.
> 
> To reduce the performance impacts on other vendors, use unlikely
> function to check flag in ISR.
> 
> Signed-off-by: Xiangliang Yu <Xiangliang.Yu@....com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c    | 6 ++++++
>  drivers/i2c/busses/i2c-designware-core.h    | 1 +
>  drivers/i2c/busses/i2c-designware-platdrv.c | 4 ++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 7441cdc..04e7b65 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -783,6 +783,9 @@ irqreturn_t i2c_dw_isr(int this_irq, void *dev_id)
>  
>  	stat = i2c_dw_read_clear_intrbits(dev);

What if the status changes right here, before you go and mask the
interrupt?

>  
> +	if (unlikely(dev->accessor_flags & ACCESS_INTR_MASK))
> +		i2c_dw_disable_int(dev);
> +
>  	if (stat & DW_IC_INTR_TX_ABRT) {
>  		dev->cmd_err |= DW_IC_ERR_TX_ABRT;
>  		dev->status = STATUS_IDLE;
> @@ -811,6 +814,9 @@ tx_aborted:
>  	if ((stat & (DW_IC_INTR_TX_ABRT | DW_IC_INTR_STOP_DET)) || dev->msg_err)
>  		complete(&dev->cmd_complete);
>  
> +	if (unlikely(dev->accessor_flags & ACCESS_INTR_MASK))
> +		dw_writel(dev, DW_IC_INTR_DEFAULT_MASK, DW_IC_INTR_MASK);

The driver disables TX interrupt when it is not needed anymore or when
TX gets aborted but the above will re-enable all interrupts regardless.
Is that the intention?

> +
>  	return IRQ_HANDLED;
>  }
>  EXPORT_SYMBOL_GPL(i2c_dw_isr);
> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index 9630222..808ef6a 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -111,6 +111,7 @@ struct dw_i2c_dev {
>  
>  #define ACCESS_SWAP		0x00000001
>  #define ACCESS_16BIT		0x00000002
> +#define ACCESS_INTR_MASK	0x00000004
>  
>  extern u32 dw_readl(struct dw_i2c_dev *dev, int offset);
>  extern void dw_writel(struct dw_i2c_dev *dev, u32 b, int offset);
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index 472b882..0c59357 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -251,6 +251,10 @@ static int dw_i2c_probe(struct platform_device *pdev)
>  		dev->rx_fifo_depth = ((param1 >> 8)  & 0xff) + 1;
>  		dev->adapter.nr = pdev->id;
>  	}
> +
> +	if (!strncmp(pdev->name, "AMD0010", 7))
> +		dev->accessor_flags |= ACCESS_INTR_MASK;
> +

Can't you put this to ->driver_data? For example it could refer to a
configuration structure that then contains quirk flags.

>  	r = i2c_dw_init(dev);
>  	if (r)
>  		return r;
> -- 
> 1.9.1
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