linux-kernel - Re: [PATCH] ARM: davinci: da850: Fix pwm name matching

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Date:   Mon, 31 Oct 2016 15:48:15 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     David Lechner <david@...hnology.com>,
        Kevin Hilman <khilman@...nel.org>
CC:     Russell King <linux@...linux.org.uk>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: davinci: da850: Fix pwm name matching

On Tuesday 25 October 2016 11:24 PM, David Lechner wrote:
> This fixes pwm name matching for DA850 familiy devices. When using device
> tree, the da850_auxdata_lookup[] table caused pwm devices to have the exact
> same name, which caused errors when trying to register the devices.
> 
> The names for clock matching in da850_clks[] also have to be updated to
> to exactly match in order for the clock lookup to work correctly.
> 
> Signed-off-by: David Lechner <david@...hnology.com>
> ---
> 
> Tested working on LEGO MINDSTORMS EV3.
> 
> 
>  arch/arm/mach-davinci/da850.c    | 10 +++++++---
>  arch/arm/mach-davinci/da8xx-dt.c | 10 +++++-----
>  2 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/mach-davinci/da850.c b/arch/arm/mach-davinci/da850.c
> index ed3d0e9..6b78a8f 100644
> --- a/arch/arm/mach-davinci/da850.c
> +++ b/arch/arm/mach-davinci/da850.c
> @@ -510,9 +510,13 @@ static struct clk_lookup da850_clks[] = {
>  	CLK("vpif",		NULL,		&vpif_clk),
>  	CLK("ahci_da850",		NULL,		&sata_clk),
>  	CLK("davinci-rproc.0",	NULL,		&dsp_clk),
> -	CLK("ehrpwm",		"fck",		&ehrpwm_clk),
> -	CLK("ehrpwm",		"tbclk",	&ehrpwm_tbclk),
> -	CLK("ecap",		"fck",		&ecap_clk),
> +	CLK("ehrpwm.0",		"fck",		&ehrpwm_clk),
> +	CLK("ehrpwm.0",		"tbclk",	&ehrpwm_tbclk),
> +	CLK("ehrpwm.1",		"fck",		&ehrpwm_clk),
> +	CLK("ehrpwm.1",		"tbclk",	&ehrpwm_tbclk),
> +	CLK("ecap.0",		"fck",		&ecap_clk),
> +	CLK("ecap.1",		"fck",		&ecap_clk),
> +	CLK("ecap.2",		"fck",		&ecap_clk),

This has exposed a limitation of DaVinci clock framework. The struct clk
are stored as a linked list themselves. So a node repeating in the table
above will create a loop in the linked list. This is easily seen on the
LCDK board. davinci_clk_disable_unused() never returns. PWMs are unused
on that board.

There is no "simple" solution to this AFAICS. One solution is to
separate the iterator from the clock hardware structure and use struct
clk_hw available in struct clk_lookup.

Or move DaVinci to common clock framework. This is of course preferred
but much more involved as all 6 supported SoCs have to be moved together.

Thanks,
Sekhar