linux-kernel - Re: [PATCH v2 2/2] i2c: mediatek: Add i2c ac-timing adjust support

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Date:   Tue, 19 May 2020 07:17:41 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Qii Wang <qii.wang@...iatek.com>
Cc:     Joe Perches <joe@...ches.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, srv_heupstream@...iatek.com,
        leilk.liu@...iatek.com,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-mediatek@...ts.infradead.org,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] i2c: mediatek: Add i2c ac-timing adjust support

On Tue, 19 May 2020 10:57:53 +0800, Qii Wang said:

> (1000000000 * (sample_cnt + 1)) / clk_src value is a 32-bit, (1000000000
> * (sample_cnt + 1)) will over 32-bit if sample_cnt is 7.
>
> I think 1000000000 and clk_src is too big, maybe I can reduce then with
> be divided all by 1000.

Yes, it's definitely too big, the 3 DIV_ROUND_UP calls in  mtk_i2c_check_ac_timing()
end up causing a build issue during modpost on a 32-bit RPi4:

ERROR: modpost: "__aeabi_uldivmod" [drivers/i2c/busses/i2c-mt65xx.ko] undefined!
ERROR: modpost: "__aeabi_ldivmod" [drivers/i2c/busses/i2c-mt65xx.ko] undefined!


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