linux-kernel - Re: [PATCH 1/3] i3c: master: Add driver for Synopsys DesignWare IP

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Date:   Wed, 8 Aug 2018 18:01:55 +0100
From:   vitor <Vitor.Soares@...opsys.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Vitor Soares <Vitor.Soares@...opsys.com>
CC:     Boris Brezillon <boris.brezillon@...tlin.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Linux Documentation List <linux-doc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Przemyslaw Sroka <psroka@...ence.com>,
        Arkadiusz Golec <agolec@...ence.com>,
        Alan Douglas <adouglas@...ence.com>,
        Bartosz Folta <bfolta@...ence.com>,
        Damian Kos <dkos@...ence.com>,
        Alicja Jurasik-Urbaniak <alicja@...ence.com>,
        Cyprian Wronka <cwronka@...ence.com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Rafal Ciepiela <rafalc@...ence.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Nishanth Menon <nm@...com>, Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        ijc+devicetree <ijc+devicetree@...lion.org.uk>,
        Kumar Gala <galak@...eaurora.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiang Lin <Xiang.Lin@...aptics.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>,
        Joao Pinto <Joao.Pinto@...opsys.com>
Subject: Re: [PATCH 1/3] i3c: master: Add driver for Synopsys DesignWare IP

Hi Andy,


On 25-07-2018 17:56, Andy Shevchenko wrote:
> On Wed, Jul 25, 2018 at 11:43 AM, Vitor Soares
> <Vitor.Soares@...opsys.com> wrote:
>> On Fri, Jul 20, 2018 at 11:57 PM, Vitor soares
>> <Vitor.Soares@...opsys.com> wrote:
>>
> Thanks for answers, my comments below.
>
>> This patch add driver for Synopsys DesignWare IP on top of
>> I3C subsystem patchset proposal V6
> ...
>
>> +#include <linux/reset.h>
>> Reset API.
>>
>> All of them required? Why?
> Thanks, got it.
>
>> There is some header files that are already included by others header files.
>> Should I add them too? it there any rule for that?
> No need.
> Usually we drop some "wired" headers (when we sure that one will
> always include the other one, like module.h vs. init.h)
>
>> +               writel(cmd->cmd_hi, master->regs + COMMAND_QUEUE_PORT);
>> +               writel(cmd->cmd_lo, master->regs + COMMAND_QUEUE_PORT);
>>
>> hmm... writesl()?
>> Is there any advantage here?
> Here maybe not. Just a material to think about. If you can refactor
> code to utilize them, good.
>
>> +       info->pid = (u64)readl(master->regs + SLV_PID_VALUE);
>>
>> Why explicit casting?
>> info->pid is u64 size.
> In C standard there is an integer promotion which allows you not to
> use explicit casting in such cases.
>
>> +       u32 r;
>> +
>> +
>> +       core_rate = clk_get_rate(master->core_clk);
>>
>> Too many blank lines in between.
>>
>>
>> For me in that way it's better to filter code parts. Do you think that is
>> not readable?
> The point is it's useless.
> On the other hand, you have a lot of inconsistency with that style.
>
>> +               p = (ret >> 6) ^ (ret >> 5) ^ (ret >> 4) ^ (ret >> 3) ^
>> +                   (ret >> 2) ^ (ret >> 1) ^ ret ^ 1;
>> +               p = p & 1;
>>
>> Is it parity calculus? Do we have something implemented in kernel already?
>>
>> Btw,
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__graphics.stanford.edu_-7Eseander_bithacks.html-23ParityNaive&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=qVuU64u9x77Y0Kd0PhDK_lpxFgg6PK9PateHwjb_DY0&m=5FpGHBbT8tYA6PB4RT_9O6PJk3v-wYcy1MV59xoqK4I&s=FSJ3EcuoxPtRJWmsk9Yt4s_UH9kxFBam01Xvas2ZFdo&e=
>> offered this
>>
>> v ^= v >> 4;
>> v &= 0xf;
>> v = (0x6996 >> v) & 1;
>>
>>
>> I search into the kernel and I didn't find any function for that. In your
>> opinion what shoud I use?
> If license of the piece above is okay to use in kernel, then
> definitely it would be better (even we might create a helper out of
> it).
>
Thanks for your comments I will take them into account for the next version.

Best regards,
Vitor Soares