linux-kernel - Re: [PATCH v3 3/7] mfd: cros_ec: spi: Make the cros_ec

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Date:	Tue, 20 May 2014 09:45:03 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	swarren@...dia.com, wsa@...-dreams.de, abrestic@...omium.org,
	dgreid@...omium.org, olof@...om.net, sjg@...omium.org,
	linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
	sameo@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/7] mfd: cros_ec: spi: Make the cros_ec_spi timeout
 more reliable

On Wed, 30 Apr 2014, Doug Anderson wrote:

> The cros_ec_spi transfer had two problems with its timeout code:
> 
> 1. It looked at the timeout even in the case that it found valid data.
> 2. If the cros_ec_spi code got switched out for a while, it's possible
>    it could get a timeout after a single loop.  Let's be paranoid and
>    make sure we do one last transfer after the timeout expires.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> Acked-by: Lee Jones <lee.jones@...aro.org>
> Reviewed-by: Simon Glass <sjg@...omium.org>
> Tested-by: Andrew Bresticker <abrestic@...omium.org>
> Tested-by: Stephen Warren <swarren@...dia.com>
> ---
> Changes in v3: None
> Changes in v2: None
> 
>  drivers/mfd/cros_ec_spi.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)

Applied, thanks.

> diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
> index a2a605d..4f863c3 100644
> --- a/drivers/mfd/cros_ec_spi.c
> +++ b/drivers/mfd/cros_ec_spi.c
> @@ -113,7 +113,9 @@ static int cros_ec_spi_receive_response(struct cros_ec_device *ec_dev,
>  
>  	/* Receive data until we see the header byte */
>  	deadline = jiffies + msecs_to_jiffies(EC_MSG_DEADLINE_MS);
> -	do {
> +	while (true) {
> +		unsigned long start_jiffies = jiffies;
> +
>  		memset(&trans, 0, sizeof(trans));
>  		trans.cs_change = 1;
>  		trans.rx_buf = ptr = ec_dev->din;
> @@ -134,12 +136,19 @@ static int cros_ec_spi_receive_response(struct cros_ec_device *ec_dev,
>  				break;
>  			}
>  		}
> +		if (ptr != end)
> +			break;
>  
> -		if (time_after(jiffies, deadline)) {
> +		/*
> +		 * Use the time at the start of the loop as a timeout.  This
> +		 * gives us one last shot at getting the transfer and is useful
> +		 * in case we got context switched out for a while.
> +		 */
> +		if (time_after(start_jiffies, deadline)) {
>  			dev_warn(ec_dev->dev, "EC failed to respond in time\n");
>  			return -ETIMEDOUT;
>  		}
> -	} while (ptr == end);
> +	}
>  
>  	/*
>  	 * ptr now points to the header byte. Copy any valid data to the

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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