linux-kernel - Re: [PATCH v2 10/10] mfd: cros_ec: spi: Add delay for asserting CS

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Date:	Wed, 13 May 2015 12:16:25 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	Stephen Barber <smbarber@...omium.org>,
	Filipe Brandenburger <filbranden@...gle.com>,
	Todd Broch <tbroch@...omium.org>,
	Alexandru M Stan <amstan@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Zhong <zyw@...k-chips.com>
Subject: Re: [PATCH v2 10/10] mfd: cros_ec: spi: Add delay for asserting CS

On Sat, 09 May 2015, Javier Martinez Canillas wrote:

> From: Alexandru M Stan <amstan@...omium.org>
> 
> Some ECs need a little time for waking up before they can accept
> SPI data at a high speed. This is configurable via a DT property
> "google,cros-ec-spi-pre-delay".
> 
> If this property isn't set, then no delay will be added. However,
> if set it will cause a delay equal to the value passed to it to
> be inserted at the beginning of a transaction.
> 
> Signed-off-by: Alexandru M Stan <amstan@...omium.org>
> Reviewed-by: Doug Anderson <dianders@...omium.org>
> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
> ---
> 
> Changes since v1: None, new patch
> ---
>  Documentation/devicetree/bindings/mfd/cros-ec.txt |  4 ++++
>  drivers/mfd/cros_ec_spi.c                         | 21 +++++++++++++++++++--
>  2 files changed, 23 insertions(+), 2 deletions(-)

Acked-by: Lee Jones <lee.jones@...aro.org>

> diff --git a/Documentation/devicetree/bindings/mfd/cros-ec.txt b/Documentation/devicetree/bindings/mfd/cros-ec.txt
> index 8009c3d87f33..1777916e9e28 100644
> --- a/Documentation/devicetree/bindings/mfd/cros-ec.txt
> +++ b/Documentation/devicetree/bindings/mfd/cros-ec.txt
> @@ -18,6 +18,10 @@ Required properties (SPI):
>  - reg: SPI chip select
>  
>  Optional properties (SPI):
> +- google,cros-ec-spi-pre-delay: Some implementations of the EC need a little
> +  time to wake up from sleep before they can receive SPI transfers at a high
> +  clock rate. This property specifies the delay, in usecs, between the
> +  assertion of the CS to the start of the first clock pulse.
>  - google,cros-ec-spi-msg-delay: Some implementations of the EC require some
>    additional processing time in order to accept new transactions. If the delay
>    between transactions is not long enough the EC may not be able to respond
> diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
> index faba03e2f1ef..16f228dc243f 100644
> --- a/drivers/mfd/cros_ec_spi.c
> +++ b/drivers/mfd/cros_ec_spi.c
> @@ -71,12 +71,15 @@
>   * @spi: SPI device we are connected to
>   * @last_transfer_ns: time that we last finished a transfer, or 0 if there
>   *	if no record
> + * @start_of_msg_delay: used to set the delay_usecs on the spi_transfer that
> + *      is sent when we want to turn on CS at the start of a transaction.
>   * @end_of_msg_delay: used to set the delay_usecs on the spi_transfer that
>   *      is sent when we want to turn off CS at the end of a transaction.
>   */
>  struct cros_ec_spi {
>  	struct spi_device *spi;
>  	s64 last_transfer_ns;
> +	unsigned int start_of_msg_delay;
>  	unsigned int end_of_msg_delay;
>  };
>  
> @@ -366,7 +369,7 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
>  	struct ec_host_request *request;
>  	struct ec_host_response *response;
>  	struct cros_ec_spi *ec_spi = ec_dev->priv;
> -	struct spi_transfer trans;
> +	struct spi_transfer trans, trans_delay;
>  	struct spi_message msg;
>  	int i, len;
>  	u8 *ptr;
> @@ -393,13 +396,23 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
>  		goto exit;
>  	}
>  
> +	/*
> +	 * Leave a gap between CS assertion and clocking of data to allow the
> +	 * EC time to wakeup.
> +	 */
> +	spi_message_init(&msg);
> +	if (ec_spi->start_of_msg_delay) {
> +		memset(&trans_delay, 0, sizeof(trans_delay));
> +		trans_delay.delay_usecs = ec_spi->start_of_msg_delay;
> +		spi_message_add_tail(&trans_delay, &msg);
> +	}
> +
>  	/* Transmit phase - send our message */
>  	memset(&trans, 0, sizeof(trans));
>  	trans.tx_buf = ec_dev->dout;
>  	trans.rx_buf = rx_buf;
>  	trans.len = len;
>  	trans.cs_change = 1;
> -	spi_message_init(&msg);
>  	spi_message_add_tail(&trans, &msg);
>  	ret = spi_sync(ec_spi->spi, &msg);
>  
> @@ -602,6 +615,10 @@ static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev)
>  	u32 val;
>  	int ret;
>  
> +	ret = of_property_read_u32(np, "google,cros-ec-spi-pre-delay", &val);
> +	if (!ret)
> +		ec_spi->start_of_msg_delay = val;
> +
>  	ret = of_property_read_u32(np, "google,cros-ec-spi-msg-delay", &val);
>  	if (!ret)
>  		ec_spi->end_of_msg_delay = val;

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