From: Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>,
Harini Katakam
<harinikatakamlinux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
"grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org"
<grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
"robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org"
<robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Pawel Moll <Pawel.Moll-5wv7dgnIgG8@public.gmane.org>,
"ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org"
<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
"galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org"
<galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
"michal.simek-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org"
<michal.simek-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org>,
"soren.brinkmann-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org"
<soren.brinkmann-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org>,
"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
"linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"vishnum-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org"
<vishnum-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C
Date: Tue, 02 Dec 2014 16:12:48 +0100 [thread overview]
Message-ID: <547DD6F0.6060006@metafoo.de> (raw)
In-Reply-To: <20141202141548.GA5883@katana>
On 12/02/2014 03:15 PM, Wolfram Sang wrote:
>>> What do you do when disable repeated start? Sending STOP and START? If
>>> so, this is really something different than repeated start. By using
>>> I2C_FUNC_I2C a user expects repeated start, so if the HW does not
>>> support it, we should say so and don't try to emulate it with something
>>> different.
>>
>> Yes, we send stop.
>
> As said before, this is wrong. Another master could interfere between
> the messages when using stop+start. This is no replacement for repeated
> start.
More importantly a lot of I2C slaves also reset their internal state machine
on a stop. So e.g. if reading a register is implemented by doing
start,write,repeated start,read,stop and you replace that with
start,write,stop,start,read,stop you'll always read register zero instead of
the register you wanted to read.
- Lars
next prev parent reply other threads:[~2014-12-02 15:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-02 10:05 [PATCH 0/4] Cadence I2C driver fixes Harini Katakam
2014-12-02 10:05 ` [PATCH 1/4] i2c: cadence: Handle > 252 byte transfers Harini Katakam
[not found] ` <1417514749-24319-1-git-send-email-harinik-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org>
2014-12-02 10:05 ` [PATCH 2/4] i2c: cadence: Set the hardware time-out register to maximum value Harini Katakam
2014-12-03 11:28 ` Wolfram Sang
2014-12-02 10:05 ` [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C Harini Katakam
2014-12-02 11:19 ` Mark Rutland
2014-12-02 12:13 ` Harini Katakam
[not found] ` <CAFcVECLtPx6shBXJbg9Uf_8fnhkMoO1zpoxGcdda7PSA7z_2rA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-12-02 12:52 ` Wolfram Sang
2014-12-02 13:10 ` Harini Katakam
[not found] ` <CAFcVECJwFoFd6GrmF282CG+fELnYb=FNCTDq=RYKky_dHha=Jg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-12-02 13:16 ` Wolfram Sang
2014-12-02 13:30 ` Harini Katakam
2014-12-02 14:15 ` Wolfram Sang
2014-12-02 15:12 ` Lars-Peter Clausen [this message]
2014-12-02 10:05 ` [PATCH 4/4] i2c: cadence: Defeature repeated start based on devicetree property Harini Katakam
[not found] ` <1417514749-24319-5-git-send-email-harinik-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org>
2014-12-02 11:21 ` Mark Rutland
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=547DD6F0.6060006@metafoo.de \
--to=lars-qo5elluwu/uelga04laivw@public.gmane.org \
--cc=Pawel.Moll-5wv7dgnIgG8@public.gmane.org \
--cc=devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org \
--cc=grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org \
--cc=harinikatakamlinux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
--cc=ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org \
--cc=linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org \
--cc=linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=mark.rutland-5wv7dgnIgG8@public.gmane.org \
--cc=michal.simek-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org \
--cc=robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
--cc=soren.brinkmann-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org \
--cc=vishnum-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org \
--cc=wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org \
/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).