From: Wolfram Sang <wsa@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Jie Deng <jie.deng@intel.com>,
linux-i2c@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, mst@redhat.com,
jasowang@redhat.com, andriy.shevchenko@linux.intel.com,
conghui.chen@intel.com, arnd@arndb.de, kblaiech@mellanox.com,
jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru,
rppt@kernel.org, loic.poulain@linaro.org, tali.perry1@gmail.com,
u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org,
yu1.wang@intel.com, shuo.a.liu@intel.com, stefanha@redhat.com,
pbonzini@redhat.com
Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver
Date: Thu, 22 Jul 2021 17:15:45 +0200 [thread overview]
Message-ID: <YPmLoeLSPS1tfYUK@ninjato> (raw)
In-Reply-To: <20210705121832.fmye5xnlbydoc5ir@vireshk-i7>
[-- Attachment #1: Type: text/plain, Size: 1554 bytes --]
Hi Viresh,
> If you look at i2c_smbus_xfer_emulated(), the command is always sent via
> msgbuf0[0]. Even in the case of I2C_SMBUS_QUICK, where we set msg[0].len = 0, we
> still send the buf. This is really confusing :(
>
> Do I understand correctly that we always need to send msg[0].buf even when
> msg[0].len is 0 ?
Nope, I think you misinterpreted that. SMBUS_QUICK will not send any
byte. After the address phase (with the RW bit as data), a STOP will
immediately follow. len = 0 will ensure that.
msgbuf0[0] is set to 'command' because every mode except SMBUS_QUICK
will need that. So, it is convenient to always do it. For SMBUS_QUICK
it is superfluous but does not hurt.
> If so, it would be difficult to implement this with the current i2c virtio
> specification, as the msg.len isn't really passed from guest to host, rather it
> is inferred using the length of the buffer itself. And so we can't really pass a
> buffer if length is 0.
And you can't leave out the buffer and assume len = 0 then? Otherwise,
you can't do SMBUS_QUICK and we need to set a struct i2c_adapter_quirks
with I2C_AQ_NO_ZERO_LEN.
Speaking of adapter quirks, currently they are not exported to
userspace. So, you can't inherit any quirks from the bus driver of the
host. It is not too bad, I think. It would mean that the host driver
will return -EOPNOTSUPP for transfers it cannot handle. Otherwise, if
quirks were inherited, we could bail out sooner at guest level, but
well...
Does this help?
Happy hacking,
Wolfram
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2021-07-22 15:15 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-23 14:19 [PATCH v10] i2c: virtio: add a virtio i2c frontend driver Jie Deng
2021-03-23 7:27 ` Viresh Kumar
2021-03-23 8:33 ` Jie Deng
2021-03-23 8:37 ` Viresh Kumar
2021-03-23 9:27 ` Arnd Bergmann
2021-03-24 1:17 ` Jie Deng
2021-03-24 4:00 ` Viresh Kumar
2021-04-15 6:45 ` Viresh Kumar
2021-04-15 6:56 ` Jie Deng
2021-04-15 7:15 ` Viresh Kumar
2021-04-15 7:21 ` Wolfram Sang
2021-04-15 7:24 ` Viresh Kumar
2021-04-15 7:28 ` Wolfram Sang
2021-04-15 7:37 ` Viresh Kumar
2021-04-15 8:15 ` Jie Deng
2021-04-15 8:18 ` Wolfram Sang
2021-04-15 8:20 ` Jie Deng
2021-05-27 6:49 ` Jie Deng
2021-05-12 1:37 ` Jie Deng
2021-03-23 9:01 ` Viresh Kumar
2021-03-23 9:38 ` Viresh Kumar
2021-03-24 0:53 ` Jie Deng
2021-03-24 3:52 ` Viresh Kumar
2021-03-24 4:00 ` Jie Deng
2021-03-24 4:02 ` Viresh Kumar
2021-03-24 4:20 ` Viresh Kumar
2021-03-24 6:05 ` Jie Deng
2021-03-24 6:09 ` Viresh Kumar
2021-03-24 6:41 ` Jie Deng
2021-03-24 6:44 ` Viresh Kumar
2021-04-14 2:07 ` Jie Deng
2021-04-14 3:52 ` Viresh Kumar
2021-04-15 6:25 ` Jie Deng
2021-04-15 3:51 ` Jason Wang
2021-04-15 6:17 ` Jie Deng
2021-06-28 8:39 ` Wolfram Sang
2021-06-28 9:01 ` Arnd Bergmann
2021-06-28 9:25 ` Wolfram Sang
2021-06-28 9:51 ` Arnd Bergmann
2021-06-28 10:13 ` Wolfram Sang
2021-06-28 11:50 ` Arnd Bergmann
2021-06-28 14:58 ` Wolfram Sang
2021-06-29 3:04 ` Jie Deng
2021-06-29 8:30 ` Wolfram Sang
2021-06-29 9:13 ` Viresh Kumar
2021-06-29 9:36 ` Wolfram Sang
2021-06-29 4:10 ` Viresh Kumar
2021-06-29 8:27 ` Wolfram Sang
2021-06-29 8:52 ` Viresh Kumar
2021-06-29 9:07 ` Wolfram Sang
2021-06-30 14:38 ` Wolfram Sang
2021-06-30 15:09 ` Viresh Kumar
2021-06-29 3:03 ` Jie Deng
2021-06-29 10:07 ` Wolfram Sang
2021-06-29 10:16 ` Viresh Kumar
2021-06-29 10:23 ` Wolfram Sang
2021-06-29 10:30 ` Viresh Kumar
2021-06-29 10:42 ` Wolfram Sang
2021-06-29 10:43 ` Wolfram Sang
2021-06-29 10:56 ` Viresh Kumar
2021-06-29 11:11 ` Wolfram Sang
2021-06-29 11:16 ` Viresh Kumar
2021-06-29 11:48 ` Wolfram Sang
2021-07-05 12:18 ` Viresh Kumar
2021-07-06 1:50 ` Jie Deng
2021-07-22 15:15 ` Wolfram Sang [this message]
2021-07-23 2:28 ` Viresh Kumar
2021-07-23 5:28 ` Viresh Kumar
2021-06-30 6:45 ` Jie Deng
2021-06-30 7:32 ` Wolfram Sang
2021-06-30 7:51 ` Jie Deng
2021-06-30 7:55 ` Arnd Bergmann
2021-06-30 8:04 ` Wolfram Sang
2021-06-30 8:07 ` Andy Shevchenko
2021-06-30 8:29 ` Arnd Bergmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YPmLoeLSPS1tfYUK@ninjato \
--to=wsa@kernel.org \
--cc=Sergey.Semin@baikalelectronics.ru \
--cc=andriy.shevchenko@linux.intel.com \
--cc=arnd@arndb.de \
--cc=bjorn.andersson@linaro.org \
--cc=conghui.chen@intel.com \
--cc=jarkko.nikula@linux.intel.com \
--cc=jasowang@redhat.com \
--cc=jie.deng@intel.com \
--cc=kblaiech@mellanox.com \
--cc=linux-i2c@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=loic.poulain@linaro.org \
--cc=mst@redhat.com \
--cc=pbonzini@redhat.com \
--cc=rppt@kernel.org \
--cc=shuo.a.liu@intel.com \
--cc=stefanha@redhat.com \
--cc=tali.perry1@gmail.com \
--cc=u.kleine-koenig@pengutronix.de \
--cc=viresh.kumar@linaro.org \
--cc=virtualization@lists.linux-foundation.org \
--cc=yu1.wang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).