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Date:   Thu, 10 Feb 2022 23:25:24 +0300
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Subject: Re: [PATCH RESEND] i2c: tegra: Add SMBus block read function
Content-Language: en-US
To:     Akhil R <akhilrajeev@nvidia.com>, christian.koenig@amd.com,
        jonathanh@nvidia.com, ldewangan@nvidia.com,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-tegra@vger.kernel.org, mperttunen@nvidia.com,
        p.zabel@pengutronix.de, sumit.semwal@linaro.org,
        thierry.reding@gmail.com
References: <20220210153603.61894-1-akhilrajeev@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
In-Reply-To: <20220210153603.61894-1-akhilrajeev@nvidia.com>
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10.02.2022 18:36, Akhil R пишет:
> Emulate SMBus block read using ContinueXfer to read the length byte
> 
> Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
> ---
>  drivers/i2c/busses/i2c-tegra.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 03cea102ab76..2941e42aa6a0 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -1233,6 +1233,11 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>  		return err;
>  
>  	i2c_dev->msg_buf = msg->buf;
> +
> +	/* The condition true implies smbus block read and len is already read */
> +	if (msg->flags & I2C_M_RECV_LEN && end_state != MSG_END_CONTINUE)
> +		i2c_dev->msg_buf = msg->buf + 1;
> +
>  	i2c_dev->msg_buf_remaining = msg->len;
>  	i2c_dev->msg_err = I2C_ERR_NONE;
>  	i2c_dev->msg_read = !!(msg->flags & I2C_M_RD);
> @@ -1389,6 +1394,15 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
>  			else
>  				end_type = MSG_END_REPEAT_START;
>  		}
> +		/* If M_RECV_LEN use ContinueXfer to read the first byte */
> +		if (msgs[i].flags & I2C_M_RECV_LEN) {
> +			ret = tegra_i2c_xfer_msg(i2c_dev, &msgs[i], MSG_END_CONTINUE);
> +			if (ret)
> +				break;
> +			/* Set the read byte as msg len */
> +			msgs[i].len = msgs[i].buf[0];
> +			dev_dbg(i2c_dev->dev, "reading %d bytes\n", msgs[i].len);
> +		}
>  		ret = tegra_i2c_xfer_msg(i2c_dev, &msgs[i], end_type);
>  		if (ret)
>  			break;
> @@ -1416,10 +1430,10 @@ static u32 tegra_i2c_func(struct i2c_adapter *adap)
>  {
>  	struct tegra_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
>  	u32 ret = I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK) |
> -		  I2C_FUNC_10BIT_ADDR |	I2C_FUNC_PROTOCOL_MANGLING;
> +		  I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
>  
>  	if (i2c_dev->hw->has_continue_xfer_support)
> -		ret |= I2C_FUNC_NOSTART;
> +		ret |= I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_READ_BLOCK_DATA;
>  
>  	return ret;
>  }

Please describe how this was tested.