linux-kernel - Re: [PATCH v2 1/2] clk: tegra: divider: Add missing check for enable-bit on rate's recalculation

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Date:   Tue, 29 Oct 2019 03:14:40 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] clk: tegra: divider: Add missing check for
 enable-bit on rate's recalculation

28.10.2019 17:27, Peter De Schrijver пишет:
> On Tue, Jul 23, 2019 at 05:52:44AM +0300, Dmitry Osipenko wrote:
>> Unset "enable" bit means that divider is in bypass mode, hence it doesn't
>> have any effect in that case. Please note that there are no known bugs
>> caused by the missing check.
>>
> 
> Technically this is not quite true, but for the purposes of CCF you can
> treat it that way. This bits defines if the value in the lower 16 bits
> of the divider register is used to configure the divider or if the
> contents of the UART DLM/DLL registers is used. So the divider isn't
> actually bypassed, it's just configured differently.
> In practice this bit is only set when the divider is non-zero when doing
> set rate. So the extra test isn't strictly needed as long as the sw
> running before the kernel also ensures the bit is only set when the
> divider is non-zero.
> 
> Acked-by: Peter De Schrijver <pdeschrijver@...dia.com>

Thank you for the clarification. I hope that bootloader doesn't enable
the divider because it looks like standard 8250 driver won't be ready
for that. But serial-tegra driver seems should be good.