Re: [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency dt-property

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: Mon, 6 Apr 2020 20:32:34 +0300	[thread overview]
Message-ID: <20200406173234.GD16885@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20200406165108.GA7646@kekkonen.localdomain>

Hi Sakari,

(CC'ing Maxime)

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.

-- 
Regards,

Laurent Pinchart