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From: Maxime Ripard <maxime@cerno.tech>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-phy@lists.infradead.org, linux-clk@vger.kernel.org,
	linux-staging@lists.linux.dev, Yong Deng <yong.deng@magewell.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Helen Koike <helen.koike@collabora.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH 01/22] clk: sunxi-ng: v3s: Make the ISP PLL clock public
Date: Thu, 16 Sep 2021 18:30:00 +0200	[thread overview]
Message-ID: <20210916163000.6ezo6muhq23bewyi@gilmour> (raw)
In-Reply-To: <YT8RnzVqLebtPMD+@aptenodytes>

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Salut Paul,

On Mon, Sep 13, 2021 at 10:53:51AM +0200, Paul Kocialkowski wrote:
> On Mon 13 Sep 21, 09:54, Maxime Ripard wrote:
> > On Fri, Sep 10, 2021 at 08:41:26PM +0200, Paul Kocialkowski wrote:
> > > In order to reparent the CSI module clock to the ISP PLL via
> > > device-tree, export the ISP PLL clock declaration in the public
> > > device-tree header.
> > 
> > You use clk_set_rate_exclusive in the ISP driver on the module clock so
> > it should prevent what you're mentioning from happening.
> 
> It does, but then it breaks display support entirely (because the DRM
> driver doesn't use clk_set_rate_exclusive).
> 
> The bottomline is that using the same PLL for both display and camera
> easily results in conflicts.

The commit log should reflect that then

> > If it doesn't, then clk_set_rate_exclusive has a bug and should be
> > fixed.
> > 
> > Either way, using assigned-clock-parents is not a good solution here
> > either, it only makes sure that this is the case when probe is run.
> 
> I'm not sure what could provide better guarantees. There is a clock
> parenting API (in the clock framework) which may, but this implies
> providing the parent clock to the driver which seems way out of line
> since this is a platform-specific matter that should certainly not
> be handled by the driver.
> 
> I also tried hardcoding the reparenting bit in the CCU driver, but
> this felt less clean than doing it in device-tree.
> 
> What do you think?

This is essentially policy, and putting it in the DT fails for the
reason we already discussed, but also if we ever want to change it for
example to optimize it a bit. In this case, we would have to deal with
the old and new DT, and the possible consequences.

So yeah, hardcoding it in the clock driver seems like a more sensible
choice.

Maxime

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  reply	other threads:[~2021-09-16 16:32 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 18:41 [PATCH 00/22] Allwinner A31/A83T MIPI CSI-2 Support and A31 ISP Support Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 01/22] clk: sunxi-ng: v3s: Make the ISP PLL clock public Paul Kocialkowski
2021-09-13  7:54   ` Maxime Ripard
2021-09-13  8:53     ` Paul Kocialkowski
2021-09-16 16:30       ` Maxime Ripard [this message]
2021-09-10 18:41 ` [PATCH 02/22] ARM: dts: sun8i: v3s: Parent the CSI module clock to the ISP PLL Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 03/22] dt-bindings: sun6i-a31-mipi-dphy: Add optional direction property Paul Kocialkowski
2021-09-13  8:00   ` Maxime Ripard
2021-09-14  7:39     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 04/22] phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI CSI-2 Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 05/22] dt-bindings: media: sun6i-a31-csi: Add MIPI CSI-2 input port Paul Kocialkowski
2021-09-13  8:09   ` Maxime Ripard
2021-09-14  7:43     ` Paul Kocialkowski
2021-09-14 12:06       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 06/22] dt-bindings: media: Add Allwinner A31 MIPI CSI-2 bindings documentation Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 07/22] media: sunxi: Add support for the A31 MIPI CSI-2 controller Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 08/22] MAINTAINERS: Add entry for the Allwinner A31 MIPI CSI-2 bridge driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 09/22] ARM: dts: sun8i: v3s: Add nodes for MIPI CSI-2 support Paul Kocialkowski
2021-09-11  2:32   ` Samuel Holland
2021-09-13  7:44     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 10/22] dt-bindings: media: Add Allwinner A83T MIPI CSI-2 bindings documentation Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 11/22] media: sunxi: Add support for the A83T MIPI CSI-2 controller Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 12/22] MAINTAINERS: Add entry for the Allwinner A83T MIPI CSI-2 bridge Paul Kocialkowski
2021-09-10 18:41 ` [PATCH NOT FOR MERGE 13/22] ARM: dts: sun8i: a83t: Add MIPI CSI-2 controller node Paul Kocialkowski
2021-09-11  2:53   ` Chen-Yu Tsai
2021-09-13  7:45     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 14/22] ARM: dts: sun8i: a83t: bananapi-m3: Enable MIPI CSI-2 with OV8865 Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 15/22] media: sunxi: Remove the sun6i-csi driver implementation Paul Kocialkowski
2021-09-13  8:17   ` Maxime Ripard
2021-09-14  8:04     ` Paul Kocialkowski
2021-09-15 19:51       ` Sakari Ailus
2021-09-10 18:41 ` [PATCH 16/22] media: sunxi: Introduce a rewritten sun6i-csi driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 17/22] dt-bindings: media: Add Allwinner A31 ISP bindings documentation Paul Kocialkowski
2021-09-13  8:18   ` Maxime Ripard
2021-09-14  7:44     ` Paul Kocialkowski
2021-09-14 12:07       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 18/22] dt-bindings: media: sun6i-a31-csi: Add ISP output port Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 19/22] soc: sunxi: mbus: Add A31 ISP compatibles to the list Paul Kocialkowski
2021-09-11  2:36   ` Samuel Holland
2021-09-13  7:45     ` Paul Kocialkowski
2021-09-13  8:32       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 20/22] staging: media: Add support for the Allwinner A31 ISP Paul Kocialkowski
2021-09-13  8:31   ` Maxime Ripard
2021-09-14  7:50     ` Paul Kocialkowski
2021-09-14 11:11       ` Laurent Pinchart
2021-09-14 11:48         ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 21/22] MAINTAINERS: Add entry for the Allwinner A31 ISP driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 22/22] ARM: dts: sun8i: v3s: Add support for the ISP Paul Kocialkowski

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