linux-kernel - Re: [PATCH 1/2] mfd: cros_ec: spi: Fix end of transfer on devices with no spi-msg-delay

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Date:	Mon, 16 Jun 2014 15:24:04 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Tomasz Figa <tomasz.figa@...il.com>, broonie@...nel.org,
	sjg@...omium.org, olof@...om.net, javier.martinez@...labora.co.uk,
	ch.naveen@...sung.com, swarren@...dotorg.org, khilman@...aro.org,
	ajaynumb@...il.com, rahul.sharma@...sung.com, tushar.b@...sung.com,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mfd: cros_ec: spi: Fix end of transfer on devices
 with no spi-msg-delay

> cros_ec_spi makes the assumption that a 0-length message will put the
> spi chip select back to normal (non cs_toggle mode).  This used to be
> the case back on kernel-3.8 on the spi-s3c64xx driver but doesn't
> appear to be true anymore.  It seems like it was a pretty questionable
> assumption to begin with, so let's fix the code to be more robust.  We
> know that a message with a single 0-length segment _will_ put things
> back in order.  Change cros_ec_spi to handle this.
> 
> This wasn't a problem on the main user of cros_ec_spi upstream (tegra)
> because it specified 'google,cros-ec-spi-msg-delay'.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>  drivers/mfd/cros_ec_spi.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)

Looks fine to me and I'm sure you've tested this on your platform.

Applied, thanks.

> diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
> index 0b8d328..0cbc3db 100644
> --- a/drivers/mfd/cros_ec_spi.c
> +++ b/drivers/mfd/cros_ec_spi.c
> @@ -266,18 +266,14 @@ static int cros_ec_command_spi_xfer(struct cros_ec_device *ec_dev,
>  		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
>  	}
>  
> -	/* turn off CS */
> +	/*
> +	 * Turn off CS, possibly adding a delay to ensure the rising edge
> +	 * doesn't come too soon after the end of the data.
> +	 */
>  	spi_message_init(&msg);
> -
> -	if (ec_spi->end_of_msg_delay) {
> -		/*
> -		 * Add delay for last transaction, to ensure the rising edge
> -		 * doesn't come too soon after the end of the data.
> -		 */
> -		memset(&trans, 0, sizeof(trans));
> -		trans.delay_usecs = ec_spi->end_of_msg_delay;
> -		spi_message_add_tail(&trans, &msg);
> -	}
> +	memset(&trans, 0, sizeof(trans));
> +	trans.delay_usecs = ec_spi->end_of_msg_delay;
> +	spi_message_add_tail(&trans, &msg);
>  
>  	final_ret = spi_sync(ec_spi->spi, &msg);
>  	ktime_get_ts(&ts);

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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