linux-kernel - Re: [V5] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate.

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Message-ID: <CAD=FV=XGivNzu_e5nrgOYkkqpWdXGgyG2MjB9xRbXm_V3JyPsw@mail.gmail.com>
Date:   Tue, 12 Jul 2022 07:11:18 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-serial@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        "Mukesh Savaliya (QUIC)" <quic_msavaliy@...cinc.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [V5] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which
 otherwise could return a sub-optimal clock rate.

Hi,

On Tue, Jul 12, 2022 at 5:45 AM Vijaya Krishna Nivarthi
<quic_vnivarth@...cinc.com> wrote:
>
> In the logic around call to clk_round_rate(), for some corner conditions,
> get_clk_div_rate() could return an sub-optimal clock rate. Also, if an
> exact clock rate was not found lowest clock was being returned.
>
> Search for suitable clock rate in 2 steps
> a) exact match or within 2% tolerance
> b) within 5% tolerance
> This also takes care of corner conditions.
>
> Fixes: c2194bc999d4 ("tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate")
> Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
> ---
> v5: corrected format specifiers for logs
> v4: replaced pr_dbg calls with dev_dbg
> v3: simplified algorithm further, fixed robot compile warnings
> v2: removed minor optimisations to make more readable
> v1: intial patch contained slightly complicated logic
> ---
>  drivers/tty/serial/qcom_geni_serial.c | 89 +++++++++++++++++++++--------------
>  1 file changed, 54 insertions(+), 35 deletions(-)

Reviewed-by: Douglas Anderson <dianders@...omium.org>