linux-kernel - Re: [PATCH 8/8] i2c: mediatek: modify bus speed calculation formula

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Date:   Fri, 16 Jul 2021 17:53:57 +0800
From:   Kewei Xu <kewei.xu@...iatek.com>
To:     Tzung-Bi Shih <tzungbi@...gle.com>
CC:     <wsa@...-dreams.de>, <matthias.bgg@...il.com>,
        <robh+dt@...nel.org>, <linux-i2c@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <leilk.liu@...iatek.com>,
        <qii.wang@...iatek.com>, <qiangming.xia@...iatek.com>,
        <ot_daolong.zhu@...iatek.com>
Subject: Re: [PATCH 8/8] i2c: mediatek: modify bus speed calculation formula

On Thu, 2021-07-15 at 15:09 +0800, Tzung-Bi Shih wrote:
> On Thu, Jul 15, 2021 at 10:32 AM Kewei Xu <kewei.xu@...iatek.com> wrote:
> > When clock-div is 0 or greater than 1, the bus speed
> > calculated by the old speed calculation formula will be
> > larger than the target speed. So we update the formula.
> The patch sounds like a fix up.  Need a "Fixes" tag.
> 
> >         for (clk_div = 1; clk_div <= max_clk_div; clk_div++) {
> >                 clk_src = parent_clk / clk_div;
> > +               i2c->ac_timing.inter_clk_div = clk_div - 1;
> Using the way to pass the parameter "inter_clk_div" to
> mtk_i2c_calculate_speed() looks like a hack.  inter_clk_div is set
> again[1] next to the for loop.
> 
> [1]: https://elixir.bootlin.com/linux/v5.14-rc1/source/drivers/i2c/busses/i2c-mt65xx.c#L831
> 
> 
> 
> I have no domain knowledge of what/how the patch fixes.  But if this
> is a standalone fixup patch, suggest separating to an independent
> patch.

Hi Tzung-Bi,

1. This Patch is not for fixing previous commit,it is just for the bad
speed formula.

2. I will fix this problem according to your suggestion in the next
patch.

Thanks
Kewei