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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	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>,
	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Lad Prabhakar <prabhakar.csengg@gmail.com>,
	Maxime Ripard <maxime@cerno.tech>
Subject: Re: [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency dt-property
Date: Tue, 7 Apr 2020 15:21:06 +0300
Message-ID: <20200407122106.GD4751@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20200407062241.GA8883@kekkonen.localdomain>

Hi Sakari,

On Tue, Apr 07, 2020 at 09:22:41AM +0300, Sakari Ailus wrote:
> On Mon, Apr 06, 2020 at 08:32:34PM +0300, Laurent Pinchart wrote:
> > On Mon, Apr 06, 2020 at 07:51:08PM +0300, Sakari Ailus wrote:
> > > On Mon, Apr 06, 2020 at 05:42:38PM +0100, Lad Prabhakar wrote:
> > > > Modes in the driver are based on xvclk frequency fixed to 24MHz, but where
> > > > as the OV5645 sensor can support the xvclk frequency ranging from 6MHz to
> > > > 24MHz. So instead making clock-frequency as dt-property just let the
> > > > driver enforce the required clock frequency.
> > > 
> > > Even if some current systems where the driver is used are using 24 MHz
> > > clock, that doesn't mean there wouldn't be systems using another frequency
> > > that the driver does not support right now.
> > > 
> > > The driver really should not set the frequency unless it gets it from DT,
> > > but I think the preferred means is to use assigned-clock-rates instead, and
> > > not to involve the driver with setting the frequency.
> > > 
> > > Otherwise we'll make it impossible to support other frequencies, at least
> > > without more or less random defaults.
> > 
> > We're running in circles here.
> > 
> > As the driver only supports 24MHz at the moment, the frequency should be
> > set by the driver, as it's a driver limitation. We can then work on
> > supporting additional frequencies, which will require DT to provide a
> > list of supported frequencies for the system, but that can be done on
> > top.
> 
> I guess it would be possible to use different external clock frequencies on
> a sensor in a given system but that seems to be a bit far fetched, to the
> extent I've never seen anyone doing that in practice.
> 
> Originally, the driver set the frequency based on the clock-frequency
> property. If we're removing that but use a fixed frequency instead, then
> how is that going to work going forward when someone adds support for other
> frequencies in the driver and has a system requiring that, while there are
> some other platforms relying on the driver setting a particular frequency?

The standard property for this is link-frequencies, not clock-frequency.
Deprecating clock-frequency now paves the way to use the standard
property later when/if someone implements support for additional
frequencies.

> Although, if you're saying that this driver only needs to work with DT that
> comes with the kernel and you don't care about DT binary compatibility,
> this would be fine.

I believe this series to not break backward compatibility, as the driver
only works with a 24MHz clock, so I expect all DTs to specify that.

-- 
Regards,

Laurent Pinchart

  reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-06 16:42 [PATCH v5 0/5] ov5645: Deprecate usage of the clock-frequency Lad Prabhakar
2020-04-06 16:42 ` [PATCH v5 1/5] media: dt-bindings: media: i2c: Deprecate usage of the clock-frequency property Lad Prabhakar
2020-04-06 17:30   ` Laurent Pinchart
2020-04-07  7:35     ` Lad, Prabhakar
2020-04-07  7:14   ` Geert Uytterhoeven
2020-04-14 13:55   ` Rob Herring
2020-04-06 16:42 ` [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency dt-property Lad Prabhakar
2020-04-06 16:51   ` Sakari Ailus
2020-04-06 17:11     ` Lad, Prabhakar
2020-04-06 17:32     ` Laurent Pinchart
2020-04-07  6:22       ` Sakari Ailus
2020-04-07 12:21         ` Laurent Pinchart [this message]
2020-04-07 15:14           ` Sakari Ailus
2020-04-14 20:55             ` Laurent Pinchart
2020-04-14 20:56               ` Laurent Pinchart
2020-04-15  8:19               ` Maxime Ripard
2020-04-15 16:27               ` Sakari Ailus
2020-04-17  2:09                 ` Laurent Pinchart
2020-04-06 17:34   ` Laurent Pinchart
2020-04-07  7:36     ` Lad, Prabhakar
2020-04-07  7:16   ` Geert Uytterhoeven
2020-04-07  7:40     ` Lad, Prabhakar
2020-04-07 12:18       ` Laurent Pinchart
2020-04-06 16:42 ` [PATCH v5 3/5] media: i2c: ov5645: Turn probe error into warning for xvclk frequency mismatch Lad Prabhakar
2020-04-06 17:35   ` Laurent Pinchart
2020-04-07  7:19   ` Geert Uytterhoeven
2020-04-07  7:43     ` Lad, Prabhakar
2020-04-06 16:42 ` [PATCH v5 4/5] ARM: dts: imx6qdl-wandboard: Drop clock-frequency property from ov5645 node Lad Prabhakar
2020-04-06 17:36   ` Laurent Pinchart
2020-04-06 16:42 ` [PATCH v5 5/5] media: dt-bindings: media: i2c: convert ov5645 bindings to json-schema Lad Prabhakar
2020-04-06 17:43   ` Laurent Pinchart
2020-04-07  7:46     ` Lad, Prabhakar
2020-04-15 14:43     ` Rob Herring

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