From: Robert Foss <robert.foss@linaro.org>
To: Maxime Ripard <maxime@cerno.tech>
Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Tomasz Figa <tfiga@chromium.org>,
Sakari Ailus <sakari.ailus@iki.fi>,
Dongchun Zhu <dongchun.zhu@mediatek.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Fabio Estevam <festevam@gmail.com>,
"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
<linux-arm-kernel@lists.infradead.org>,
linux-media <linux-media@vger.kernel.org>
Subject: Re: [PATCH v6 1/3] media: dt-bindings: ov8856: Document YAML bindings
Date: Tue, 7 Apr 2020 13:29:05 +0200 [thread overview]
Message-ID: <CAG3jFyvd32pWppubMoOoyH9eO2XLjwUXMC7p4xtv8m+JkPv6vw@mail.gmail.com> (raw)
In-Reply-To: <20200407083647.4mocdl7aqa3x737q@gilmour.lan>
Hey Maixme & Sakari,
On Tue, 7 Apr 2020 at 10:36, Maxime Ripard <maxime@cerno.tech> wrote:
>
> Hi Sakari,
>
> On Mon, Apr 06, 2020 at 11:35:07AM +0300, Sakari Ailus wrote:
> > > But that 19.2MHz is not a limitation of the device itself, it's a
> > > limitation of our implementation, so we can instead implement
> > > something equivalent in Linux using a clk_set_rate to 19.2MHz (to make
> > > sure that our parent clock is configured at the right rate) and the
> > > clk_get_rate and compare that to 19.2MHz (to make sure that it's not
> > > been rounded too far apart from the frequency we expect).
> > >
> > > This is doing exactly the same thing, except that we don't encode our
> > > implementation limitations in the DT, but in the driver instead.
> >
> > What I really wanted to say that a driver that doesn't get the clock
> > frequency from DT but still sets that frequency is broken.
> >
> > This frequency is highly system specific, and in many cases only a certain
> > frequency is usable, for a few reasons: On many SoCs, not all common
> > frequencies can be used (e.g. 9,6 MHz, 19,2 MHz and 24 MHz; while others
> > are being used as well), and then that frequency affects the usable CSI-2
> > bus frequencies directly --- and of those, only safe, known-good ones
> > should be used. IOW, getting the external clock frequency wrong typically
> > has an effect that that none of the known-good CSI-2 bus clock frequencies
> > are available.
>
> So clock-frequency is not about the "Frequency of the xvclk clock in
> Hertz", but the frequency at which that clock must run on this
> particular SoC / board to be functional?
>
> If so, then yeah, we should definitely keep it, but the documentation
> of the binding should be made clearer as well.
>
Alright so, let me summarise the desired approach then.
ACPI:
- Fetch the "clock-frequency" property
- Verify it to be 19.2Mhz
DT:
- Fetch the "clock-frequency" property
- Verify it to be 19.2Mhz
- Get xvclk clock
- Get xvclk clock rate
- Verify xvclk clock rate to be 19.2Mhz
Since the xvclk clock isn't available under ACPI, this is how the two
cases would be distinguished between.
Does this sound about right?
> assigned-clock-rates should still go away though.
Ack.
>
> Maxime
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next prev parent reply other threads:[~2020-04-07 11:29 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-31 13:33 [PATCH v3 0/3] media: ov8856: Add devicetree support Robert Foss
2020-03-31 13:33 ` [PATCH v6 1/3] media: dt-bindings: ov8856: Document YAML bindings Robert Foss
2020-03-31 15:12 ` Marco Felsch
2020-04-02 9:57 ` Robert Foss
2020-04-03 19:21 ` Marco Felsch
2020-04-01 8:07 ` Maxime Ripard
2020-04-02 10:10 ` Robert Foss
2020-04-03 23:27 ` Sakari Ailus
2020-04-04 9:34 ` Maxime Ripard
2020-04-06 8:25 ` Robert Foss
2020-04-06 8:35 ` Sakari Ailus
2020-04-07 8:36 ` Maxime Ripard
2020-04-07 11:29 ` Robert Foss [this message]
2020-04-07 12:32 ` Maxime Ripard
2020-04-07 15:47 ` Robert Foss
2020-04-07 16:39 ` Sakari Ailus
2020-04-07 16:46 ` Tomasz Figa
2020-04-07 17:20 ` Sakari Ailus
2020-04-08 12:21 ` Maxime Ripard
2020-04-08 12:35 ` Tomasz Figa
2020-04-08 13:43 ` Maxime Ripard
2020-04-08 15:28 ` Sakari Ailus
2020-04-08 15:30 ` Sakari Ailus
2020-04-08 16:34 ` Andy Shevchenko
2020-04-15 10:18 ` Maxime Ripard
2020-04-15 11:10 ` Robert Foss
2020-04-15 16:16 ` Sakari Ailus
2020-04-20 15:02 ` Maxime Ripard
2020-04-09 8:32 ` Robert Foss
2020-04-07 16:20 ` Sakari Ailus
2020-04-04 9:23 ` Maxime Ripard
2020-03-31 13:33 ` [PATCH v3 2/3] media: ov8856: Add devicetree support Robert Foss
2020-03-31 14:01 ` Andy Shevchenko
2020-04-06 13:37 ` Robert Foss
2020-04-06 15:06 ` Andy Shevchenko
2020-04-06 15:25 ` Robert Foss
2020-04-03 23:33 ` Sakari Ailus
2020-03-31 13:33 ` [PATCH v3 3/3] media: ov8856: Implement sensor module revision identification Robert Foss
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