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 17:19:09 +0000
From:   "Vijaya Krishna Nivarthi (Temp) (QUIC)" <quic_vnivarth@...cinc.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        "Vijaya Krishna Nivarthi (Temp) (QUIC)" <quic_vnivarth@...cinc.com>
CC:     "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>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "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.



> -----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.
Thank you,
Vijay/


All errors (new ones prefixed by >>):

   arm-linux-gnueabi-ld: arm-linux-gnueabi-ld: DWARF error: could not find abbrev number 121
   drivers/tty/serial/qcom_geni_serial.o: in function `find_clk_rate_in_tol':
>> qcom_geni_serial.c:(.text+0x764): undefined reference to `__aeabi_uldivmod'