linux-kernel - Re: [V2] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate.

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Date:   Thu, 30 Jun 2022 14:57:03 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     "Vijaya Krishna Nivarthi (Temp) (QUIC)" <quic_vnivarth@...cinc.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        "agross@...nel.org" <agross@...nel.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "konrad.dybcio@...ainline.org" <konrad.dybcio@...ainline.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Mukesh Savaliya (QUIC)" <quic_msavaliy@...cinc.com>,
        "mka@...omium.org" <mka@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>
Subject: Re: [V2] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which
 otherwise could return a sub-optimal clock rate.

Hi,

On Thu, Jun 30, 2022 at 10:19 AM Vijaya Krishna Nivarthi (Temp) (QUIC)
<quic_vnivarth@...cinc.com> wrote:
>
> > -----Original Message-----
> > From: Greg KH <gregkh@...uxfoundation.org>
> > Sent: Thursday, June 30, 2022 8:31 PM
> > To: Vijaya Krishna Nivarthi (Temp) (QUIC) <quic_vnivarth@...cinc.com>
> > Cc: agross@...nel.org; bjorn.andersson@...aro.org;
> > konrad.dybcio@...ainline.org; jirislaby@...nel.org; linux-arm-
> > msm@...r.kernel.org; linux-serial@...r.kernel.org; linux-
> > kernel@...r.kernel.org; Mukesh Savaliya (QUIC)
> > <quic_msavaliy@...cinc.com>; dianders@...omium.org;
> > mka@...omium.org; swboyd@...omium.org
> > Subject: Re: [V2] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which
> > otherwise could return a sub-optimal clock rate.
> >
> > WARNING: This email originated from outside of Qualcomm. Please be wary
> > of any links or attachments, and do not enable macros.
> >
> > On Wed, Jun 29, 2022 at 03:30:41PM +0530, Vijaya Krishna Nivarthi 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.
> > >
> > > Reported-by: kernel test robot <lkp@...el.com>
> >
> > Did the test robot really report the original issue, or just the v2 change?
> >
> > thanks,
> >
> > greg k-h
>
> Test robot raised error for v1 patch and (I think) it got addressed in v2 with call to div_u64.
> V2 doesn't have this error but other warnings which I am addressing along with other feedback.
> Below is the error raised for v1.

I think the adding of the "Reported-by" only really makes sense if the
commit landed and then you fixed the robot-reported bug in a separate
commit. If it reported problems in v1 and you fix them in v2 you
shouldn't add the tag.

-Doug