linux-kernel - RE: [PATCH V7 3/5] i2c: tegra: Add DMA Support

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Message-ID: <BYAPR12MB3398C3E7C5842C698B5CA1CCC2910@BYAPR12MB3398.namprd12.prod.outlook.com>
Date:   Thu, 31 Jan 2019 03:34:59 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>,
        Shardar Mohammed <smohammed@...dia.com>,
        Timo Alho <talho@...dia.com>
CC:     "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH V7 3/5] i2c: tegra: Add DMA Support

> I2C_INT_ALL_PACKETS_XFER_COMPLETE shall be masked for the PIO mode
> I2C_INT_PACKET_XFER_COMPLETE shall be masked for the DMA mode, if I'm not missing something.
>
for packets with repeated start or continue xfer, PACKET_XFER_COMPLETE will be triggers
for packets with stop bit, both PACKET_XFER_COMPLETE and ALL_PACKET_XFER_COMPLETE will be triggered.
To be align with what PIO mode is doing, will not use ALL_PACKETS_XFER_COMPLETE for DMA in next version. 

>
> Handle the error-case here:
>
>	if (i2c_dev->msg_err != I2C_ERR_NONE) {
>		dev_err(i2c_dev->dev, "i2c dma transfer failed\n");
>		goto i2c_recover;
>	}
>
>...
>	<--- end of tegra_i2c_xfer_msg() -->
>
>	if (likely(i2c_dev->msg_err == I2C_ERR_NONE))
>		return 0;
>
> i2c_recover:
>	tegra_i2c_init(i2c_dev);
>	/* start recovery upon arbitration loss in single master mode */
>	if (i2c_dev->msg_err == I2C_ERR_ARBITRATION_LOST) {
>		if (!i2c_dev->is_multimaster_mode)
>			return tegra_i2c_issue_bus_clear(i2c_dev);
>		return -EAGAIN;
>	}
>	if (i2c_dev->msg_err == I2C_ERR_NO_ACK) {
>		if (msg->flags & I2C_M_IGNORE_NAK)
>			return 0;
>		return -EREMOTEIO;
>	}
>
>	return -EIO;

When DMA transfer timeout, no need to check for ARB LOST or NO_ACK as if any of those interrupts trigger interrupt handler will terminate dmaengine and completes so DMA timeout will not be seen in those cases and falls thru msg_err check