From: Daniel Stodden <daniel.stodden@gmail.com>
To: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH i2c-tools] i2ctransfer: add support for I2C_M_RECV_LEN
Date: Mon, 3 Aug 2020 00:30:46 -0700 [thread overview]
Message-ID: <C82A0A94-A06B-4D42-B71B-F14D48D5E029@gmail.com> (raw)
In-Reply-To: <20200802213828.GB13339@kunai>
> On Aug 2, 2020, at 2:38 PM, Wolfram Sang <wsa+renesas@sang-engineering.com> wrote:
>
> Hi Daniel,
>
>>> + __u16 len = recv_len ? msgs[i].buf[0] + 1 : msgs[i].len;
>>
>> This is post-ioctl()? (Sorry, still not familiar enough with i2c-tools.)
>
> Yes, read buffers are only printed after the ioctl. And 'print_msgs' is
> probably the most complex function within this tool :/
>
>> It isn’t wrong, but shouldn’t be necessary.
>> Unless the adapter driver you’re using went astray. Not ruling that out.
>
> I have just checked existing I2C_M_RECV_LEN handling. Quite some drivers
> do it wrong. And there is no consistency in what they return. Lots of
> things to fix there...
Would be curious about what variants are there.
Note that msgs[i].len isn’t updated, you only get <extra_bytes> of data back,
so the difference would be severe: msgs[i].len is what guides copy_to_user().
https://github.com/torvalds/linux/blob/master/drivers/i2c/i2c-dev.c#L301
Daniel
next prev parent reply other threads:[~2020-08-03 7:30 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-02 19:28 [PATCH i2c-tools] i2ctransfer: add support for I2C_M_RECV_LEN Wolfram Sang
2020-08-02 20:28 ` Daniel Stodden
2020-08-02 21:38 ` Wolfram Sang
2020-08-03 7:30 ` Daniel Stodden [this message]
2020-08-03 8:38 ` Wolfram Sang
2020-08-03 20:25 ` Daniel Stodden
2020-08-03 20:45 ` Wolfram Sang
2020-08-03 19:14 ` Wolfram Sang
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