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Date:   Sat, 12 Feb 2022 19:15:20 +0300
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Subject: Re: [PATCH RESEND] i2c: tegra: Add SMBus block read function
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To:     Akhil R <akhilrajeev@nvidia.com>,
        "christian.koenig@amd.com" <christian.koenig@amd.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        Mikko Perttunen <mperttunen@nvidia.com>,
        "p.zabel@pengutronix.de" <p.zabel@pengutronix.de>,
        "sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
        "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        Svyatoslav Ryhel <clamor95@gmail.com>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>
References: <20220210153603.61894-1-akhilrajeev@nvidia.com>
 <ae6d300f-962d-9731-bb78-3594b4c31aea@gmail.com>
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From:   Dmitry Osipenko <digetx@gmail.com>
In-Reply-To: <DM5PR12MB18502CF86E602F7071A1EA58C0309@DM5PR12MB1850.namprd12.prod.outlook.com>
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11.02.2022 12:11, Akhil R пишет:
>> 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.
> This is tested using an I2C EEPROM to emulate SMBus block read in which
> we read the first byte as the length of bytes to read. This is an expected
> feature for NVIDIA Grace chipset where there will be an actual SMBus device.

We have several Tegra30+ tablets that have EC on SMBus. Svyatoslav tried
your I2C patch + [1] on Asus TF201 and reported that it breaks EC. Any
idea why it doesn't work?

[1]
https://github.com/grate-driver/linux/commit/aa8d71f5a960ef40503e5448c622d62d1c53a2c0