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Date:   Tue, 21 Nov 2017 19:54:08 -0800
From:   Benson Leung <bleung@google.com>
To:     Shawn Nematbakhsh <shawnn@chromium.org>
Cc:     linux-kernel@vger.kernel.org, lee.jones@linaro.org,
        jonathanh@nvidia.com, briannorris@chromium.org, bleung@google.com,
        bleung@chromium.org
Subject: Re: [PATCH] mfd: cros ec: spi: Fix "in progress" error signaling
Message-ID: <20171122035408.GA121077@decatoncale.mtv.corp.google.com>
References: <20170927213527.31416-1-shawnn@chromium.org>
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Hi Shawn,

On Wed, Sep 27, 2017 at 02:35:27PM -0700, Shawn Nematbakhsh wrote:
> For host commands that take a long time to process, cros ec can return
> early by signaling a EC_RES_IN_PROGRESS result. The host must then poll
> status with EC_CMD_GET_COMMS_STATUS until completion of the command.
>=20
> None of the above applies when data link errors are encountered. When
> errors such as EC_SPI_PAST_END are encountered during command
> transmission, it usually means the command was not received by the EC.
> Treating such errors as if they were 'EC_RES_IN_PROGRESS' results is
> almost always the wrong decision, and can result in host commands
> silently being lost.
>=20
> Reported-and-tested-by: Jon Hunter <jonathanh@nvidia.com>
> Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>

Acked-by: Benson Leung <bleung@chromium.org>

> ---
>  drivers/mfd/cros_ec_spi.c | 52 ++++++++++++++++++++++-------------------=
------
>  1 file changed, 24 insertions(+), 28 deletions(-)
>=20
> diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
> index c9714072e224..d019b5b00b67 100644
> --- a/drivers/mfd/cros_ec_spi.c
> +++ b/drivers/mfd/cros_ec_spi.c
> @@ -377,6 +377,7 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device=
 *ec_dev,
>  	u8 *ptr;
>  	u8 *rx_buf;
>  	u8 sum;
> +	u8 rx_byte;
>  	int ret =3D 0, final_ret;
> =20
>  	len =3D cros_ec_prepare_tx(ec_dev, ec_msg);
> @@ -421,25 +422,22 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_devi=
ce *ec_dev,
>  	if (!ret) {
>  		/* Verify that EC can process command */
>  		for (i =3D 0; i < len; i++) {
> -			switch (rx_buf[i]) {
> -			case EC_SPI_PAST_END:
> -			case EC_SPI_RX_BAD_DATA:
> -			case EC_SPI_NOT_READY:
> -				ret =3D -EAGAIN;
> -				ec_msg->result =3D EC_RES_IN_PROGRESS;
> -			default:
> +			rx_byte =3D rx_buf[i];
> +			if (rx_byte =3D=3D EC_SPI_PAST_END  ||
> +			    rx_byte =3D=3D EC_SPI_RX_BAD_DATA ||
> +			    rx_byte =3D=3D EC_SPI_NOT_READY) {
> +				ret =3D -EREMOTEIO;
>  				break;
>  			}
> -			if (ret)
> -				break;
>  		}
> -		if (!ret)
> -			ret =3D cros_ec_spi_receive_packet(ec_dev,
> -					ec_msg->insize + sizeof(*response));
> -	} else {
> -		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
>  	}
> =20
> +	if (!ret)
> +		ret =3D cros_ec_spi_receive_packet(ec_dev,
> +				ec_msg->insize + sizeof(*response));
> +	else
> +		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
> +
>  	final_ret =3D terminate_request(ec_dev);
> =20
>  	spi_bus_unlock(ec_spi->spi->master);
> @@ -508,6 +506,7 @@ static int cros_ec_cmd_xfer_spi(struct cros_ec_device=
 *ec_dev,
>  	int i, len;
>  	u8 *ptr;
>  	u8 *rx_buf;
> +	u8 rx_byte;
>  	int sum;
>  	int ret =3D 0, final_ret;
> =20
> @@ -544,25 +543,22 @@ static int cros_ec_cmd_xfer_spi(struct cros_ec_devi=
ce *ec_dev,
>  	if (!ret) {
>  		/* Verify that EC can process command */
>  		for (i =3D 0; i < len; i++) {
> -			switch (rx_buf[i]) {
> -			case EC_SPI_PAST_END:
> -			case EC_SPI_RX_BAD_DATA:
> -			case EC_SPI_NOT_READY:
> -				ret =3D -EAGAIN;
> -				ec_msg->result =3D EC_RES_IN_PROGRESS;
> -			default:
> +			rx_byte =3D rx_buf[i];
> +			if (rx_byte =3D=3D EC_SPI_PAST_END  ||
> +			    rx_byte =3D=3D EC_SPI_RX_BAD_DATA ||
> +			    rx_byte =3D=3D EC_SPI_NOT_READY) {
> +				ret =3D -EREMOTEIO;
>  				break;
>  			}
> -			if (ret)
> -				break;
>  		}
> -		if (!ret)
> -			ret =3D cros_ec_spi_receive_response(ec_dev,
> -					ec_msg->insize + EC_MSG_TX_PROTO_BYTES);
> -	} else {
> -		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
>  	}
> =20
> +	if (!ret)
> +		ret =3D cros_ec_spi_receive_response(ec_dev,
> +				ec_msg->insize + EC_MSG_TX_PROTO_BYTES);
> +	else
> +		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
> +
>  	final_ret =3D terminate_request(ec_dev);
> =20
>  	spi_bus_unlock(ec_spi->spi->master);
> --=20
> 2.12.2
>=20

--=20
Benson Leung
Staff Software Engineer
Chrome OS Kernel
Google Inc.
bleung@google.com
Chromium OS Project
bleung@chromium.org

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