linux-kernel - Re: [PATCH 2/2] clk: samsung: exynos-clkout: convert to module driver

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Date:   Wed, 28 Oct 2020 23:07:33 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Kukjin Kim <kgene@...nel.org>,
        linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 2/2] clk: samsung: exynos-clkout: convert to module driver

On Thu, Oct 01, 2020 at 06:56:46PM +0200, Krzysztof Kozlowski wrote:
> The Exynos clkout driver depends on board input clock (typically XXTI or
> XUSBXTI), however on Exynos4 boards these clocks were modeled as part of
> SoC clocks (Exynos4 clocks driver).  Obviously this is not proper, but
> correcting it would break DT backward compatibility.
> 
> Both drivers - clkout and Exynos4 clocks - register the clock providers
> with CLK_OF_DECLARE/OF_DECLARE_1 so their order is fragile (in the
> Makefile clkout is behind Exynos4 clock).  It will work only if the
> Exynos4 clock driver comes up before clkout.
> 
> A change in DTS adding input clock reference to Exynos4 clocks input
> PLL, see reverted commit eaf2d2f6895d ("ARM: dts: exynos: add input
> clock to CMU in Exynos4412 Odroid"), caused probe reorder: the clkout
> appeared before Exynos4 clock provider.  Since clkout depends on Exynos4
> clocks and does not support deferred probe, this did not work and caused
> later failure of usb3503 USB hub probe which needs clkout:
> 
>     [    5.007442] usb3503 0-0008: unable to request refclk (-517)
> 
> The Exynos clkout driver is not a critical/core clock so there is
> actually no problem in instantiating it later, as a regular module.
> This removes specific probe ordering and adds support for probe
> deferral.
> 
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> ---
>  drivers/clk/samsung/clk-exynos-clkout.c | 198 +++++++++++++++++-------
>  1 file changed, 141 insertions(+), 57 deletions(-)

Applied (with fixes pointed out by Sylwester).

Best regards,
Krzysztof