From: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: "Andy Shevchenko" <andriy.shevchenko@intel.com>,
linux-media@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
"Rob Herring" <robh+dt@kernel.org>,
"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
"Wolfram Sang" <wsa@kernel.org>,
"Matti Vaittinen" <Matti.Vaittinen@fi.rohmeurope.com>,
"Laurent Pinchart" <laurent.pinchart+renesas@ideasonboard.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Peter Rosin" <peda@axentia.se>,
"Liam Girdwood" <lgirdwood@gmail.com>,
"Mark Brown" <broonie@kernel.org>,
"Sakari Ailus" <sakari.ailus@linux.intel.com>,
"Michael Tretter" <m.tretter@pengutronix.de>,
"Shawn Tu" <shawnx.tu@intel.com>,
"Hans Verkuil" <hverkuil@xs4all.nl>,
"Mike Pagano" <mpagano@gentoo.org>,
"Krzysztof Hałasa" <khalasa@piap.pl>,
"Marek Vasut" <marex@denx.de>,
"Luca Ceresoli" <luca@lucaceresoli.net>
Subject: Re: [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support
Date: Thu, 19 Jan 2023 14:08:06 +0100 [thread overview]
Message-ID: <20230119140806.6b926cad@booty> (raw)
In-Reply-To: <ddbf82d0-155f-9189-44df-1f796c028b53@ideasonboard.com>
Hi Tomi, Andy,
On Thu, 19 Jan 2023 14:39:09 +0200
Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> wrote:
> On 19/01/2023 10:21, Luca Ceresoli wrote:
> > Hi Andy,
> >
> > On Wed, 18 Jan 2023 19:39:46 +0200
> > Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
> >
> >> On Wed, Jan 18, 2023 at 06:17:53PM +0100, Luca Ceresoli wrote:
> >>> On Wed, 18 Jan 2023 16:23:53 +0200
> >>> Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
> >>
> >> ...
> >>
> >>>>> +A typical example follows.
> >>>>> +
> >>>>> +Topology::
> >>>>> +
> >>>>> + Slave X @ 0x10
> >>>>> + .-----. |
> >>>>> + .-----. | |---+---- B
> >>>>> + | CPU |--A--| ATR |
> >>>>> + `-----' | |---+---- C
> >>>>> + `-----' |
> >>>>> + Slave Y @ 0x10
> >>>>> +
> >>>>> +Alias table:
> >>>>> +
> >>>>> +.. table::
> >>>>> +
> >>>>> + ====== =====
> >>>>> + Client Alias
> >>>>> + ====== =====
> >>>>> + X 0x20
> >>>>> + Y 0x30
> >>>>> + ====== =====
> >>>>> +
> >>>>> +Transaction:
> >>>>> +
> >>>>> + - Slave X driver sends a transaction (on adapter B), slave address 0x10
> >>>>> + - ATR driver rewrites messages with address 0x20, forwards to adapter A
> >>>>> + - Physical I2C transaction on bus A, slave address 0x20
> >>>>> + - ATR chip propagates transaction on bus B with address translated to 0x10
> >>>>> + - Slave X chip replies on bus B
> >>>>> + - ATR chip forwards reply on bus A
> >>>>> + - ATR driver rewrites messages with address 0x10
> >>>>> + - Slave X driver gets back the msgs[], with reply and address 0x10
> >>>>
> >>>> I'm not sure I got the real / virtual status of the adapters. Are the B and C
> >>>> virtual ones, while A is the real?
> >>>
> >>> Let me reply, as I wrote these docs back at the times and thus I feel
> >>> guilty in case that's unclear. :)
> >>>
> >>> I don't like the word "virtual" in this situation. A, B and C are all
> >>> physical busses, made of copper and run by electrons on PCBs. B and C
> >>> are the "remote" or "downstream" busses (w.r.t. the CPU), where the i2c
> >>> devices are and where transactions happen using the address that the
> >>> chip responds to. A is the "local" or "upstream" bus that is driven
> >>> directly by the CPU (*) and where address aliases are used. Using
> >>> aliases there is necessary because using address 0x10 would be
> >>> ambiguous as there are two 0x10 chips out there.
> >>>
> >>> (*) There could be more layers of course, but still A is "closer to the
> >>> CPU than B and C", for the sake of completeness.
> >>
> >> Can the diagram and/or text be updated to elaborate this?
> >
> > Let's see whether the text below is better. I haven't changed the
> > image, I don't think we can do much more in ASCII, but maybe we can
> > replace it with an SVG [0]?
> >
> > [0]
> > https://github.com/lucaceresoli/docs/blob/master/video-serdes-linux/images/i2c-ti.svg
> >
> > A typical example follows.
> >
> > Topology::
> >
> > Slave X @ 0x10
> > .-----. |
> > .-----. | |---+---- B
> > | CPU |--A--| ATR |
> > `-----' | |---+---- C
> > `-----' |
> > Slave Y @ 0x10
>
> Slightly beside the point of this discussion, but one thing (I think) I
> tried to highlight in some older cover letter was that we don't really
> have the above structure. We have something like this (a quick edit, sorry):
>
> .------. Slave X @ 0x10
> .------. | FPDS | |
> .-----. | FPDD |-F1-`------'---+---- B
> | CPU |--A--| ATR |
> `-----' | |-F2-.------.---+---- C
> `------' | FPDS | |
> `------' Slave Y @ 0x10
>
> Where FPDD = Deserializer, FPDS = Serializer, F1/F2 = FPD-Link bus 1/2.
>
> So the ATR functionality is in the deserializer, but the actual remote
> i2c bus is on the serializer.
I'd rather say that the ATF functionality is in the sum of ser+des as
they really cooperate. But this is kind of philosophical. :) What
matters is that it's worth mentioning that the "ATR" box is actually an
abstract visualization of a feature that is provided by two or more
chips (in the known universe, at least).
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
next prev parent reply other threads:[~2023-01-19 13:09 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-18 12:40 [PATCH v7 0/7] i2c-atr and FPDLink Tomi Valkeinen
2023-01-18 12:40 ` [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support Tomi Valkeinen
2023-01-18 14:23 ` Andy Shevchenko
2023-01-18 17:17 ` Luca Ceresoli
2023-01-18 17:39 ` Andy Shevchenko
2023-01-19 8:21 ` Luca Ceresoli
2023-01-19 10:09 ` Tomi Valkeinen
2023-01-19 11:35 ` Luca Ceresoli
2023-01-19 12:22 ` Tomi Valkeinen
2023-01-19 13:00 ` Luca Ceresoli
2023-01-20 9:55 ` Laurent Pinchart
2023-01-20 13:58 ` Luca Ceresoli
2023-01-19 12:39 ` Tomi Valkeinen
2023-01-19 13:08 ` Luca Ceresoli [this message]
2023-01-19 10:01 ` Tomi Valkeinen
2023-01-20 15:58 ` Andy Shevchenko
2023-01-20 16:00 ` Tomi Valkeinen
2023-01-18 12:40 ` [PATCH v7 2/7] dt-bindings: media: add TI DS90UB913 FPD-Link III Serializer Tomi Valkeinen
2023-01-18 12:40 ` [PATCH v7 3/7] dt-bindings: media: add TI DS90UB953 " Tomi Valkeinen
2023-01-18 12:40 ` [PATCH v7 4/7] dt-bindings: media: add TI DS90UB960 FPD-Link III Deserializer Tomi Valkeinen
2023-01-19 23:24 ` Laurent Pinchart
2023-01-18 12:40 ` [PATCH v7 5/7] media: i2c: add DS90UB960 driver Tomi Valkeinen
2023-01-18 15:48 ` Andy Shevchenko
2023-01-19 16:27 ` Tomi Valkeinen
2023-01-19 23:19 ` Laurent Pinchart
2023-01-20 16:47 ` Andy Shevchenko
2023-01-25 11:15 ` Tomi Valkeinen
2023-01-25 12:10 ` Andy Shevchenko
2023-01-25 13:33 ` Tomi Valkeinen
2023-01-25 14:49 ` Andy Shevchenko
2023-01-25 15:14 ` Tomi Valkeinen
2023-01-25 15:27 ` Andy Shevchenko
2023-01-26 8:41 ` Tomi Valkeinen
2023-01-26 10:21 ` Andy Shevchenko
2023-01-26 10:51 ` Laurent Pinchart
2023-01-27 8:24 ` Tomi Valkeinen
2023-01-27 9:15 ` Andy Shevchenko
2023-02-08 15:10 ` Tomi Valkeinen
2023-02-09 10:54 ` Laurent Pinchart
2023-01-18 12:40 ` [PATCH v7 6/7] media: i2c: add DS90UB913 driver Tomi Valkeinen
2023-01-20 0:03 ` Laurent Pinchart
2023-01-20 7:04 ` Tomi Valkeinen
2023-01-20 9:06 ` Laurent Pinchart
2023-01-18 12:40 ` [PATCH v7 7/7] media: i2c: add DS90UB953 driver Tomi Valkeinen
2023-01-20 0:34 ` Laurent Pinchart
2023-01-20 8:13 ` Tomi Valkeinen
2023-01-20 9:23 ` Laurent Pinchart
2023-01-18 16:01 ` [PATCH v7 0/7] i2c-atr and FPDLink Andy Shevchenko
2023-01-18 17:28 ` Tomi Valkeinen
2023-01-18 17:43 ` Andy Shevchenko
2023-01-19 8:43 ` Luca Ceresoli
2023-01-19 12:40 ` Tomi Valkeinen
2023-01-19 13:19 ` Luca Ceresoli
2023-01-20 16:00 ` Andy Shevchenko
2023-01-20 16:17 ` Luca Ceresoli
2023-01-20 16:20 ` Tomi Valkeinen
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