linux-kernel - Re: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array

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Date:   Fri, 31 Aug 2018 10:01:44 +0200
From:   Jerome Forissier <jerome.forissier@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Anson Huang <anson.huang@....com>,
        Fabio Estevam <fabio.estevam@....com>,
        Peng Fan <peng.fan@....com>, Rob Herring <robh@...nel.org>
Cc:     dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array

On 08/31/2018 03:29 AM, Stephen Boyd wrote:
> Quoting Peng Fan (2018-08-12 18:15:41)
>> Hi Anson,
>>
>>>>> -----Original Message-----
>>>>> From: Anson Huang
>>>>> Sent: 2018年8月8日 12:39
>>>>> To: shawnguo@...nel.org; s.hauer@...gutronix.de;
>>>>> kernel@...gutronix.de; Fabio Estevam <fabio.estevam@....com>;
>>>>> mturquette@...libre.com; sboyd@...nel.org;
>>>>> linux-arm-kernel@...ts.infradead.org;
>>>>> linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org
>>>>> Cc: dl-linux-imx <linux-imx@....com>
>>>>> Subject: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array
>>>>>
>>>>> Clock framework will enable those clocks registered with
>>>>> CLK_IS_CRITICAL flag, so no need to have clks_init_on array during
>>>>> clock
>>>> initialization now.
>>>>
>>>> Will it be more flexible to parse dts saying "critical-clocks = <xxx>"
>>>> or "init-on-arrary=<xxx>"
>>>> and enable those clocks?
>>>
>>> Parsing the clocks arrays from dtb is another way of enabling critical clocks, but
>>> for current i.MX6/7 platforms, we implement it in same way as most of other
>>> SoCs, currently I did NOT see any necessity of putting them in dtb, just adding
>>> flag during clock registering is more simple, if there is any special requirement
>>> for different clocks set to be enabled, then we can add support to enable the
>>> method of parsing critical-clocks from dtb. Just my two cents.
>>
>> Thinking about OP-TEE want to use one device, but it's clocks are registered
>> by Linux, because there is no module in Linux side use it, it will shutdown the clock,
>> which cause OP-TEE could not access the device.
>>
>> Then people have to modify clk code to add CLK_IS_CRITICAL flag to make sure
>> the clocks are not shutdown by Linux.
>>
>> However adding a new property in clk node and let driver code parse the dts,
>> there is no need to modify clk driver code when OP-TEE needs another device clock.
>>
> 
> If OP-TEE needs linux to keep things on then why can't the OP-TEE driver
> in Linux probe, acquire clocks, and keep the clks enabled forever?

Sounds reasonable, but how could this be done without introducing
platform-specific stuff in the OP-TEE driver?

> 
> 
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