From: Krzysztof Kozlowski <krzk@kernel.org>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
Rob Herring <robh+dt@kernel.org>, Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Fabio Estevam <festevam@gmail.com>,
NXP Linux Team <linux-imx@nxp.com>,
linux-media@vger.kernel.org, devicetree@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for IMX258 sensor
Date: Fri, 2 Oct 2020 14:15:11 +0200 [thread overview]
Message-ID: <20201002121511.GA7285@pi3> (raw)
In-Reply-To: <20200929110255.GJ26842@paasikivi.fi.intel.com>
On Tue, Sep 29, 2020 at 02:02:55PM +0300, Sakari Ailus wrote:
> On Tue, Sep 29, 2020 at 11:46:36AM +0200, Krzysztof Kozlowski wrote:
> > On Tue, Sep 29, 2020 at 12:40:46PM +0300, Sakari Ailus wrote:
> > > On Tue, Sep 29, 2020 at 11:18:46AM +0200, Krzysztof Kozlowski wrote:
> > > > On Tue, 29 Sep 2020 at 11:15, Sakari Ailus <sakari.ailus@linux.intel.com> wrote:
> > > > >
> > > > > Hi Krzysztof,
> > > > >
> > > > > On Wed, Sep 23, 2020 at 05:21:26PM +0200, Krzysztof Kozlowski wrote:
> > > > > > Add bindings for the IMX258 camera sensor. The bindings, just like the
> > > > > > driver, are quite limited, e.g. do not support regulator supplies.
> > > > > >
> > > > > > Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
> > > > > >
> > > > > > ---
> > > > > >
> > > > > > Changes since v3:
> > > > > > 1. Document also two lane setup.
> > > > > >
> > > > > > Changes since v2:
> > > > > > 1. Remove clock-frequency, add reset GPIOs, add supplies.
> > > > >
> > > > > Oops. I missed this one.
> > > > >
> > > > > How does the driver know the appropriate clock frequency for the platform
> > > > > if it's not in DT? The sensor supports a range of frequencies, not a single
> > > > > frequency.
> > > > >
> > > > > Could you add clock-frequency back?
> > > >
> > > > Not really, it was removed on Rob's request. The bindings do not
> > > > describe driver's behavior so how the driver gets frequency should not
> > > > be part of the bindings. Also it's not a real problem - the driver
> > > > just calls clk_get_rate().
> > >
> > > How is the rate determined? I mean, many ISPs or CSI-2 receivers that
> > > provide the clock are also capable of using a variety of frequencies. But
> > > only one can be used on the platform in general.
> >
> > Having "clock-frequency" property in DTS did not solve that. It has no
> > effect on actual frequency.
>
> It's up to the driver to do what's needed, yes.
>
> Please see examples in e.g. drivers/media/i2c/ov8856.c and
> Documentation/devicetree/bindings/media/i2c/ov8856.yaml .
It seems the ov8856 driver uses this property in different way than
imx258 driver. It is more appropriate and quite similar to clock
providers and buses - to set the desired frequency on input clock.
Therefore what is the point of using this DT property comparing to
assigned-clock-rates?
It's the same. So let's use generic (already documented)
assigned-clock-rates.
For your question (not related to the bindings but to driver
implementation): "How is the rate determined?", simple: clk_get_rate.
The driver then uses it like this:
if (clk_get_rate() != only_working_configuration_hz)
return -EINVAL;
From the bindings point of view, the clock can be anything within a
range of sensor's accepted values. The clock frequency is a property of
a clock, not of a sensor. Therefore for HW description it should be
described in the clock bindings, not in the sensor bindings.
To summarize, the "clock-frequency" property of sensor node:
1. As a way to configure the clock should be replaced with
assigned-clock properties,
2. As a way to describe the hardware is simply invalid. It is not a HW
description, because HW requires just a clock of frequency within
given range, not a fixed frequency clock.
Consider the example:
camera@1a {
compatible = "sony,imx258";
reg = <0x1a>;
clocks = <&imx258_clk>;
clock-names = "clk";
/* Oscillator on camera board */
imx258_clk: clk {
compatible = "fixed-clock";
#clock-cells = <0>;
clock-frequency = <19200000>;
};
port {
...
};
};
What is the point to add "clock-frequency" property to the camera
itself, since it is already clearly defined by the clock?
Or another example:
camera@1a {
compatible = "sony,imx258";
reg = <0x1a>;
clocks = <&iclk 0>;
clock-names = "clk";
assigned-clocks = <&clk 0>;
assigned-clock-rates = <19200000>;
port {
...
};
};
Again, no reason for artificial clock-frequency property. It is not part
of HW description of the sensor.
Best regards,
Krzysztof
next prev parent reply other threads:[~2020-10-02 12:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 15:21 [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for IMX258 sensor Krzysztof Kozlowski
2020-09-23 15:21 ` [PATCH v4 2/4] media: i2c: imx258: add support for binding via device tree Krzysztof Kozlowski
2020-09-23 15:21 ` [PATCH v4 3/4] media: i2c: imx258: simplify getting state container Krzysztof Kozlowski
2020-09-23 15:21 ` [PATCH v4 4/4] media: i2c: imx258: get clock from device properties and enable it via runtime PM Krzysztof Kozlowski
2020-09-29 9:17 ` Sakari Ailus
2020-09-29 9:24 ` Krzysztof Kozlowski
2020-09-28 18:46 ` [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for IMX258 sensor Rob Herring
2020-09-29 9:15 ` Sakari Ailus
2020-09-29 9:18 ` Krzysztof Kozlowski
2020-09-29 9:40 ` Sakari Ailus
2020-09-29 9:46 ` Krzysztof Kozlowski
2020-09-29 11:02 ` Sakari Ailus
2020-10-02 12:15 ` Krzysztof Kozlowski [this message]
2020-09-29 9:43 ` Sakari Ailus
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