linux-kernel - Re: [PATCH 1/4] clk: propagate parent change up one level

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Message-id: <5344198B.2030604@samsung.com>
Date:	Tue, 08 Apr 2014 17:45:15 +0200
From:	Tomasz Figa <t.figa@...sung.com>
To:	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Cc:	mturquette@...aro.org, kgene.kim@...sung.com, inki.dae@...sung.com,
	sw0312.kim@...sung.com, kyungmin.park@...sung.com,
	airlied@...ux.ie, rob.herring@...xeda.com,
	sylvester.nawrocki@...il.com, a.hajda@...sung.com, kishon@...com
Subject: Re: [PATCH 1/4] clk: propagate parent change up one level

Hi,

On 04.04.2014 16:53, Tomasz Stanislawski wrote:
> This patch adds support for propagation of setup of clock's parent one level
> up.
>
> This feature is helpful when a driver changes topology of its clocks using
> clk_set_parent().  The problem occurs when on one platform/SoC driver's clock
> is located at MUX output but on the other platform/SoC there is a gated proxy
> clock between the MUX and driver's clock.  In such a case, driver's code has to
> be modified to use one clock for enabling and the other clock for setup of a
> parent.
>
> The code updates are avoided by propagating setup of a parent up one level.
>
> Additionally, this patch adds CLK_SET_PARENT_PARENT (sorry for naming) flag to
> inform clk-core that clk_set_parent() should be propagated.
>
> Signed-off-by: Tomasz Stanislawski <t.stanislaws@...sung.com>
> ---
>   drivers/clk/clk.c            |    6 ++++++
>   include/linux/clk-provider.h |    1 +
>   2 files changed, 7 insertions(+)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index dff0373..53bbfda 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1737,6 +1737,12 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
>
>   	/* try finding the new parent index */
>   	if (parent) {
> +		if ((clk->flags & CLK_SET_PARENT_PARENT)
> +		    && clk->num_parents == 1) {
> +			ret = clk_set_parent(clk->parent, parent);
> +			goto out;
> +		}
> +
>   		p_index = clk_fetch_parent_index(clk, parent);
>   		p_rate = parent->rate;
>   		if (p_index < 0) {
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 5119174..daa0b03 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -30,6 +30,7 @@
>   #define CLK_GET_RATE_NOCACHE	BIT(6) /* do not use the cached clk rate */
>   #define CLK_SET_RATE_NO_REPARENT BIT(7) /* don't re-parent on rate change */
>   #define CLK_GET_ACCURACY_NOCACHE BIT(8) /* do not use the cached clk accuracy */
> +#define CLK_SET_PARENT_PARENT	BIT(9) /* propagate parent change up one level */
>
>   struct clk_hw;
>   struct dentry;
>

This would be very useful, at least on Exynos platforms, with 
mux-div-gate clock paths. PARENT_PARENT sounds a bit funny, though.

Reviewed-by: Tomasz Figa <t.figa@...sung.com>

Best regards,
Tomasz
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