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

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Date:   Tue, 1 Nov 2016 16:01:30 +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 Monday 31 October 2016 08:18 PM, David Lechner wrote:
> On 10/31/2016 05:18 AM, Sekhar Nori wrote:
>> 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
>>
>>
> 
> The simple solution for now could be to make child clocks for each of
> these that simply enable the parent clock. e.g. ehrpwm0_clk and
> ehpwm1_clk are children of ehrpwm_clk, etc.

That sounds good. I saw the v2 patch you sent and it looks good. I
noticed that aemif clock is repeated in da850.c too. That needs fixing.

> Looking at da830.c, it looks like the solution was to make multiple
> clocks that use the same LPSC, but this does not seem right to me.

The PWM clock definitions there are definitely wrong. It should be
fixed. Looks like its been like that forever.

Thanks,
Sekhar