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Date:   Tue, 10 Mar 2020 13:29:34 +0100
From:   Wolfram Sang <wsa@the-dreams.de>
To:     Rishi Gupta <gupt21@gmail.com>
Cc:     jikos@kernel.org, benjamin.tissoires@redhat.com,
        wsa+renesas@sang-engineering.com, gregkh@linuxfoundation.org,
        linux-i2c@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] HID: mcp2221: add usb to i2c-smbus host bridge
Message-ID: <20200310122934.GA13896@ninjato>
References: <1580185137-11255-1-git-send-email-gupt21@gmail.com>
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> +	if (num == 1) {
> +		if (msgs->flags & I2C_M_RD) {
> +			ret = mcp_i2c_smbus_read(mcp, msgs, MCP2221_I2C_RD_DATA,
> +							0, 0, NULL);
> +		} else {
> +			ret = mcp_i2c_write(mcp, msgs, MCP2221_I2C_WR_DATA, 1);
> +		}
> +		if (ret)
> +			goto exit;
> +		ret = num;
> +	} else if (num == 2) {
> +		/* Ex transaction; send reg address and read its contents */
> +		if (msgs[0].addr == msgs[1].addr &&
> +			!(msgs[0].flags & I2C_M_RD) &&
> +			 (msgs[1].flags & I2C_M_RD)) {
> +
> +			ret = mcp_i2c_write(mcp, &msgs[0],
> +						MCP2221_I2C_WR_NO_STOP, 0);
> +			if (ret)
> +				goto exit;
> +
> +			ret = mcp_i2c_smbus_read(mcp, &msgs[1],
> +						MCP2221_I2C_RD_RPT_START,
> +						0, 0, NULL);
> +			if (ret)
> +				goto exit;
> +			ret = num;
> +		} else {
> +			dev_err(&adapter->dev,
> +				"unsupported multi-msg i2c transaction\n");
> +			ret = -EOPNOTSUPP;
> +		}
> +	} else {
> +		dev_err(&adapter->dev,
> +			"unsupported multi-msg i2c transaction\n");
> +		ret = -EOPNOTSUPP;
> +	}

Have a look at struct i2c_adapter_quirks and especially the flags to let
the I2C core do the sanity checks from here.


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