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From: Maxime Ripard <maxime@cerno.tech>
To: Sakari Ailus <sakari.ailus@iki.fi>
Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Robert Foss <robert.foss@linaro.org>,
	Tomasz Figa <tfiga@chromium.org>,
	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 10:36:47 +0200
Message-ID: <20200407083647.4mocdl7aqa3x737q@gilmour.lan> (raw)
In-Reply-To: <20200406083506.GE6127@valkosipuli.retiisi.org.uk>

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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.

assigned-clock-rates should still go away though.

Maxime

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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 [this message]
2020-04-07 11:29               ` Robert Foss
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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