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Subject: Re: [PATCH] clk: vc5: fix output disabling when enabling a FOD
To:     Adam Ford <aford173@gmail.com>
Cc:     linux-clk <linux-clk@vger.kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20210409125732.376589-1-luca@lucaceresoli.net>
 <CAHCN7xLSgkJKs-8baa9O303=x1jB=7khedyBMcoHP_33Obqdbg@mail.gmail.com>
From:   Luca Ceresoli <luca@lucaceresoli.net>
Message-ID: <a1ecb31b-8969-62d6-fccf-9196e595dd21@lucaceresoli.net>
Date:   Wed, 5 May 2021 18:55:32 +0200
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Hi Adam,

thanks for reviewing.

On 05/05/21 14:59, Adam Ford wrote:

[...]

>> @@ -581,6 +585,23 @@ static int vc5_clk_out_prepare(struct clk_hw *hw)
>>         unsigned int src;
>>         int ret;
>>
>> +       /*
>> +        * When enabling a FOD, all currently enabled FODs are briefly
>> +        * stopped in order to synchronize all of them. This causes a clock
>> +        * disruption to any unrelated chips that might be already using
>> +        * other clock outputs. Bypass the sync feature to avoid the issue,
>> +        * which is possible on the VersaClock 6E family via reserved
>> +        * registers.
>> +        */
> 
> Thanks for the comments here.  I with IDT/Renesas would better
> document this.

The support person who assisted me said he would suggest to document
this better. It would be good if you could add to their work.

> I might see if I can convince one of the hardware guys
> at my office to test the impact of radiated emissions.

That would be interesting to know, sure.

-- 
Luca