From: richardcochran@gmail.com (Richard Cochran)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH 1/2] macb: Add 1588 support in Cadence GEM.
Date: Thu, 8 Sep 2016 21:06:25 +0200 [thread overview]
Message-ID: <20160908190624.GA5237@netboy> (raw)
In-Reply-To: <CAFcVECJxJgJUeO4=yudwTj5NkxDob5tCZaom9YTqWWmtt7ajFw@mail.gmail.com>
On Thu, Sep 08, 2016 at 10:22:43AM +0530, Harini Katakam wrote:
> >> + /* get GEM internal time */
> >> + sech = gem_readl(bp, TSH);
> >> + secl = gem_readl(bp, TSL);
> >
> > Does reading TSH latch the time? The TRM is silent about that, and
> > most other designs latch on reading the LSB.
>
> No, it does not latch the time.
> When doing a read + adjust + write, this will
> mean there's room for some error.
It also means that you will have to handle when the TSL value
overflows into TSH. That means reading TSH twice, once before and
once after reading TSL and retrying if needed.
The code as written above will produce apparent jumps backwards in
time, whenever the overflow occurs between the two read operations.
Thanks,
Richard
next prev parent reply other threads:[~2016-09-08 19:06 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-02 12:53 [RFC PATCH 1/2] macb: Add 1588 support in Cadence GEM Andrei Pistirica
2016-09-02 12:53 ` [RFC PATCH 2/2] macb: Enable 1588 support in SAMA5D2 platform Andrei Pistirica
2016-09-06 7:43 ` Harini Katakam
2016-09-06 16:37 ` Richard Cochran
2016-09-09 14:08 ` Andrei Pistirica
2016-09-06 7:36 ` [RFC PATCH 1/2] macb: Add 1588 support in Cadence GEM Harini Katakam
2016-09-06 15:48 ` Richard Cochran
2016-09-08 4:52 ` Harini Katakam
2016-09-08 7:44 ` Richard Cochran
2016-09-08 19:06 ` Richard Cochran [this message]
2016-09-09 13:51 ` Andrei Pistirica
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=20160908190624.GA5237@netboy \
--to=richardcochran@gmail.com \
--cc=linux-arm-kernel@lists.infradead.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).