linux-kernel - Re: [PATCH RESEND] i2c: tegra: Add SMBus block read function

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Date:   Sat, 12 Feb 2022 19:20:44 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Akhil R <akhilrajeev@...dia.com>,
        "christian.koenig@....com" <christian.koenig@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Mikko Perttunen <mperttunen@...dia.com>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: Re: [PATCH RESEND] i2c: tegra: Add SMBus block read function

12.02.2022 19:15, Dmitry Osipenko пишет:
> 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@...dia.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

Ah, I see now that I2C_FUNC_SMBUS_WRITE_BLOCK_DATA not supported, we
should check again without the write then.