Re: [PATCH v2 2/7] dt-bindings: clock: renesas,r9a06g032-sysctrl: Add h2mode property

From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Herve Codina <herve.codina@bootlin.com>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Magnus Damm <magnus.damm@gmail.com>,
	Gareth Williams <gareth.williams.jx@renesas.com>,
	linux-renesas-soc@vger.kernel.org, linux-clk@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-usb@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>
Subject: Re: [PATCH v2 2/7] dt-bindings: clock: renesas,r9a06g032-sysctrl: Add h2mode property
Date: Tue, 22 Nov 2022 11:23:23 +0100	[thread overview]
Message-ID: <978fb5a1-64f3-7ee6-3e98-1e31b8b6a88b@linaro.org> (raw)
In-Reply-To: <CAMuHMdV1Y4Ldq2Hu5X8awTOWYTHq4DPYWCMkyg-9TQY=DaxREg@mail.gmail.com>

On 22/11/2022 10:01, Geert Uytterhoeven wrote:
>>>>> The h2mode bit (and probably a few other controls we haven't figured out
>>>>> yet) in the sysctrl must be set before any of the USB devices is active.
>>>>> Hence it's safest for the sysctrl to do this before any of the USB drivers
>>>>> probes.
>>>>
>>>> Again, this does not differ from many, many of other devices. All of
>>>> them must set something in system controller block, before they start
>>>> operating (or at specific time). It's exactly the same everywhere.
>>>
>>> The issue here is that there are two _different drivers_ (USB host
>>> and device). When both are modular, and the driver that depends on the
>>> sysctrl setting is loaded second, you have a problem: the sysctrl change
>>> must not be done when the first driver is already using the hardware.
>>>
>>> Hence the sysctrl driver should take care of it itself during early
>>> initialization (it's the main clock controller, so it's a dependency
>>> for all other I/O device drivers).
>>
>> I assumed you have there bit for the first device (which can switch
>> between USB host and USB device) to choose appropriate mode. The
>> bindings also expressed this - "the USBs are". Never said anything about
>> dependency between these USBs.
>>
>> Are you saying that the mode for first device cannot be changed once the
>> second device (which is only host) is started? IOW, the mode setup must
>> happen before any of these devices are started?
> 
> Exactly.
> 
>> Anyway with sysctrl approach you will have dependency and you cannot
>> rely on clock provider-consumer relationship to order that dependency.
>> What if you make all clocks on and do not take any clocks in USB device?
> 
> Enabling the clocks does not have anything to do with this ordering.

That was the argument from Herve, that ordering is guaranteed by clocks.

> Clock consumers that are part of the clock domain are probed after
> clock providers.  If the clock is missing, that would be an incorrect
> description in DTS.

If not clocks, what else is guaranteeing the ordering? You did not
express it in DT.

Best regards,
Krzysztof