linux-kernel - Re: [PATCH] clk: mediatek: mt8186: Change I2C 4/5/6 ap clocks parent to infra

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Date:   Wed, 25 Oct 2023 09:50:11 +0000
From:   Yu-chang Lee (李禹璋) 
        <Yu-chang.Lee@...iatek.com>
To:     "wenst@...omium.org" <wenst@...omium.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Chun-Jie Chen (陳浚桀) 
        <Chun-Jie.Chen@...iatek.com>,
        Miles Chen (陳民樺) 
        <Miles.Chen@...iatek.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH] clk: mediatek: mt8186: Change I2C 4/5/6 ap clocks parent
 to infra

On Tue, 2023-10-24 at 17:20 +0800, Chen-Yu Tsai wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On Tue, Oct 24, 2023 at 3:47 PM Yu-chang Lee (李禹璋)
> <Yu-chang.Lee@...iatek.com> wrote:
> >
> > On Tue, 2023-10-24 at 10:58 +0800, Chen-Yu Tsai wrote:
> > > On Tue, Oct 24, 2023 at 10:52 AM Stephen Boyd <sboyd@...nel.org>
> > > wrote:
> > > >
> > > > Quoting Chen-Yu Tsai (2023-10-19 22:06:35)
> > > > > On Thu, Oct 19, 2023 at 8:49 PM AngeloGioacchino Del Regno
> > > > > <angelogioacchino.delregno@...labora.com> wrote:
> > > > > >
> > > > > > Fix the parenting of clocks imp_iic_wrap_ap_clock_i2c{4-6}, 
> as
> > > > > > those
> > > > > > are effectively parented to infra_ao_i2c{4-6} and not to
> the
> > > > > > I2C_AP.
> > > > > > This permits the correct (and full) enablement and
> disablement
> > > > > > of the
> > > > > > I2C4, I2C5 and I2C6 bus clocks, satisfying the whole clock
> tree
> > > > > > of
> > > > > > those.
> > > > > >
> > > > > > As an example, when requesting to enable
> > > > > > imp_iic_wrap_ap_clock_i2c4:
> > > > > >
> > > > > > Before: infra_ao_i2c_ap -> imp_iic_wrap_ap_clock_i2c4
> > > > > > After:  infra_ao_i2c_ap -> infra_ao_i2c4 ->
> > > > > > imp_iic_wrap_ap_clock_i2c4
> > > > > >
> > > > > > Fixes: 66cd0b4b0ce5 ("clk: mediatek: Add MT8186 imp i2c
> wrapper
> > > > > > clock support")
> > > > > > Signed-off-by: AngeloGioacchino Del Regno <
> > > > > > angelogioacchino.delregno@...labora.com>
> > > > >
> > > > > I'm curious about what led to discovering this error?
> > > > >
> > > >
> > > > Is that an acked-by?
> > >
> > > MediaTek engineers are saying the original code already matches
> the
> > > documentation provided by their hardware engineers. I'm trying to
> get
> > > them to respond on the mailing list.
> > >
> > > ChenYu
> > >
> > After checking with I2C clock hardware designer there is no
> > infra_ao_i2c{4-6} clock gate in between. And the clock document at
> hand
> > aslo shows the same result. Generallly speaking, we would like to
> keep
> > sw setting align with the hardware design document. I would
> recommand
> > not to change this part of code, but enable infra_ao_i2c{4-6} prior
> to
> > the usage of imp_iic_wrap_ap_clock_i2c clock.
> 
> Are infra_ao_i2c{4-6} actually used by the hardware? If so, for what
> purpose?

According to hardware designer it servers no purpose. Just a legacy of
previous design...

> If it is actually needed by the hardware and it is not in the
> existing path,
> then it needs to be described in the device tree and handled by the
> driver.
> 
> ChenYu

After reviewing hardware design diagram, hardware designer concludes
that the clock tree is indeed

top_i2c -> infra_ao_i2c{4-6}
top_i2c -> infra_ao_i2c_ap -> imp_iic_wrap_ap_clock_i2c{4-6}

so I think we should keep this clock relation unchanged.

Thanks
YuChang