linux-kernel - RE: [PATCH 2/2] i2c: qup: support SMBus block read

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Message-ID: <000b01d1aa8b$7317a300$5946e900$@codeaurora.org>
Date:	Tue, 10 May 2016 12:43:21 +0530
From:	"Sricharan" <sricharan@...eaurora.org>
To:	"'Naveen Kaje'" <nkaje@...eaurora.org>, <wsa@...-dreams.de>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc:	<rruigrok@...eaurora.org>, <timur@...eaurora.org>,
	<cov@...eaurora.org>, "'Andy Gross'" <andy.gross@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-arm-msm@...r.kernel.org>
Subject: RE: [PATCH 2/2] i2c: qup: support SMBus block read

+additional lists

> I2C QUP driver relies on SMBus emulation support from the framework.
> To handle SMBus block reads, the driver should check I2C_M_RECV_LEN flag
> and should read the first byte received as the message length.
> 
> The driver configures the QUP hardware to read one byte. Once the message
> length is known from this byte, the QUP hardware is configured to read the
> rest.
> 
> Signed-off-by: Naveen Kaje <nkaje@...eaurora.org>
> ---
>  drivers/i2c/busses/i2c-qup.c | 95 ++++++++++++++++++++++++++++++-------
> -------
>  1 file changed, 66 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
index
> ef31b26..2658b67 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -526,38 +526,49 @@ static int qup_i2c_set_tags(u8 *tags, struct
> qup_i2c_dev *qup,
> 
>  	int last = (qup->blk.pos == (qup->blk.count - 1)) && (qup->is_last);
> 
> -	if (qup->blk.pos == 0) {
> -		tags[len++] = QUP_TAG_V2_START;
> -		tags[len++] = addr & 0xff;
> +	/* Handle SMBus block data read */
> +	if ((msg->flags & I2C_M_RD) && (msg->flags & I2C_M_RECV_LEN)
> &&
> +	    (msg->len > 1)) {
> +		tags[len++] = QUP_TAG_V2_DATARD_STOP;
> +		data_len = qup_i2c_get_data_len(qup);
> +		tags[len++] = data_len - 1;
> +	} else {
> +		if (qup->blk.pos == 0) {
> +			tags[len++] = QUP_TAG_V2_START;
> +			tags[len++] = addr & 0xff;
> 
> -		if (msg->flags & I2C_M_TEN)
> -			tags[len++] = addr >> 8;
> -	}
> +			if (msg->flags & I2C_M_TEN)
> +				tags[len++] = addr >> 8;
> +		}
> 
> -	/* Send _STOP commands for the last block */
> -	if (last) {
> -		if (msg->flags & I2C_M_RD)
> -			tags[len++] = QUP_TAG_V2_DATARD_STOP;
> -		else
> -			tags[len++] = QUP_TAG_V2_DATAWR_STOP;
> -	} else {
> -		if (msg->flags & I2C_M_RD)
> +		/* Send _STOP commands for the last block */
> +		if ((msg->flags & I2C_M_RD)
> +			&& (msg->flags & I2C_M_RECV_LEN)) {
>  			tags[len++] = QUP_TAG_V2_DATARD;
> -		else
> -			tags[len++] = QUP_TAG_V2_DATAWR;
> -	}
> +		} else if (last) {
> +			if (msg->flags & I2C_M_RD)
> +				tags[len++] = QUP_TAG_V2_DATARD_STOP;
> +			else
> +				tags[len++] = QUP_TAG_V2_DATAWR_STOP;
> +		} else {
> +			if (msg->flags & I2C_M_RD)
> +				tags[len++] = QUP_TAG_V2_DATARD;
> +			else
> +				tags[len++] = QUP_TAG_V2_DATAWR;
> +		}
> 
> -	data_len = qup_i2c_get_data_len(qup);
> +		data_len = qup_i2c_get_data_len(qup);
> 
> -	/* 0 implies 256 bytes */
> -	if (data_len == QUP_READ_LIMIT)
> -		tags[len++] = 0;
> -	else
> -		tags[len++] = data_len;
> +		/* 0 implies 256 bytes */
> +		if (data_len == QUP_READ_LIMIT)
> +			tags[len++] = 0;
> +		else
> +			tags[len++] = data_len;
> 
> -	if ((msg->flags & I2C_M_RD) && last && is_dma) {
> -		tags[len++] = QUP_BAM_INPUT_EOT;
> -		tags[len++] = QUP_BAM_FLUSH_STOP;
> +		if ((msg->flags & I2C_M_RD) && last && is_dma) {
> +			tags[len++] = QUP_BAM_INPUT_EOT;
> +			tags[len++] = QUP_BAM_FLUSH_STOP;
> +		}
>  	}
> 
   Will it look simpler if we add a qup_i2c_set_tags_smb instead and add an
   Comment ? Here it is not clear how this is different from a normal read.

<snip..>

> +
> +		/* Handle SMBus block read length */
> +		if ((msg->flags & I2C_M_RECV_LEN) && (msg->len == 1)) {
> +			if (msg->buf[0] > I2C_SMBUS_BLOCK_MAX) {
> +				ret = -EPROTO;
> +				goto err;
> +			}
> +			msg->len += msg->buf[0];
> +			qup->pos = 0;
> +			qup_i2c_set_read_mode_v2(qup, msg->len);
> +			qup_i2c_issue_xfer_v2(qup, msg);
> +			ret = qup_i2c_wait_for_complete(qup, msg);
> +			if (ret)
> +				goto err;
> +			qup_i2c_set_blk_data(qup, msg);
> +		}
>  	} while (qup->blk.pos < qup->blk.count);
       
         When v2 mode is not supported this should return an error,
         in qup_i2c_xfer for msg->flags & I2C_M_RECV_LEN

Regards,
 Sricharan