linux-kernel - Re: [PATCH v6 00/41] ARM: davinci: convert to common clock framework

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Date:   Thu, 25 Jan 2018 10:18:19 -0600
From:   David Lechner <david@...hnology.com>
To:     Sekhar Nori <nsekhar@...com>, Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Adam Ford <aford173@...il.com>, linux-clk@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 00/41] ARM: davinci: convert to common clock framework

On 01/25/2018 06:53 AM, Sekhar Nori wrote:
> On Wednesday 24 January 2018 01:33 PM, Bartosz Golaszewski wrote:
>> 2018-01-23 21:23 GMT+01:00 David Lechner <david@...hnology.com>:
>>> On 01/23/2018 02:05 PM, David Lechner wrote:
>>>>
>>>> On 01/23/2018 02:01 PM, David Lechner wrote:
>>>>>
>>>>> On 01/23/2018 01:53 PM, Bartosz Golaszewski wrote:
>>>>>>
>>>>>>
>>>>>> In the mdio case - the problem is that devm_clk_get() doesn't fail,
>>>>>> but somehow the clock doesn't end up in the list of the device's
>>>>>> clocks - which is why it's not enabled by pm_runtime_get_sync().
>>>>>>
>>>>>
>>>>>
>>>>> Right. This is because devm_clk_get() now finds the clock via device
>>>>> tree instead of a clkdev lookup entry. However, I think that the PM
>>>>> notifier registered in arch/arm/mach-davinci/pm_domain.c only uses
>>>>> the clkdev lookup to match the con_id and does not use device tree.
>>>>> The same thing is happing in mdio, emac and lcdc.
>>>>>
>>>>
>>>> Minor correction: It looks like emac doesn't do this because it doesn't
>>>> have a con_id of "fck". But, the same clock is shared by emac and mdio, so
>>>> since mdio enables the clock, emac doesn't notice or care that it did
>>>> not enable the clock itself.
>>>
>>>
>>> How about using pm_clk_add_clk() in these drivers to explicitly use the
>>> clocks for power management instead of relying on pm_clk_add_notifier()
>>> to do this implicitly?
>>
>> Yes, this sounds good.
> 
> Looking at how pm_clk_notify() in clock_ops.c uses con_id[] list, right
> now pm_runtime() will work only for clocks which have con_id (from the
> list above) mentioned in DT. Since clk_find() mandates con_id match when
> its available, NULL con_id does not match.
> 
> For simple devices like DaVinci which uses just one clock for power
> management per device (multiple devices might share a clock, but not
> other way around as far as I recall, anyway I will double check this
> assertion), the attached patch should make EMAC work.
> 
> That still leaves why lcdc does not work. One difference is it uses
> PSC1. Are there other devices in PSC1 which work (just to rule out any
> thing wrong with PSC1 handling).
> 
> Thanks,
> Sekhar
> 
> ---8<---
> diff --git a/arch/arm/mach-davinci/pm_domain.c b/arch/arm/mach-davinci/pm_domain.c
> index 78eac2c0c146..0dce7397856d 100644
> --- a/arch/arm/mach-davinci/pm_domain.c
> +++ b/arch/arm/mach-davinci/pm_domain.c
> @@ -23,7 +23,6 @@ static struct dev_pm_domain davinci_pm_domain = {
>   
>   static struct pm_clk_notifier_block platform_bus_notifier = {
>   	.pm_domain = &davinci_pm_domain,
> -	.con_ids = { "fck", "master", "slave", NULL },
>   };
>   
>   static int __init davinci_pm_runtime_init(void)
> 
> 

Won't this cause *all* clocks, not just PSC clocks, to be used for power management?

Some examples of devices with more than just the PSC clock are SATA and the USB PHY.