linux-kernel - Re: [PATCH v6 4/4] mmc: mediatek: Add subsys clock control for MT8192 msdc

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Message-ID: <CANMq1KAnG5Z=GZBqUhz9FdWx9-bSkUs3FgZnURjvzeHTrpTWGw@mail.gmail.com>
Date:   Wed, 14 Oct 2020 16:01:38 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Matthias Brugger <matthias.bgg@...il.com>
Cc:     Wenbin Mei <wenbin.mei@...iatek.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Chaotian Jing <chaotian.jing@...iatek.com>,
        linux-mmc@...r.kernel.org,
        Devicetree List <devicetree@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>
Subject: Re: [PATCH v6 4/4] mmc: mediatek: Add subsys clock control for MT8192 msdc

On Wed, Oct 14, 2020 at 3:44 PM Matthias Brugger <matthias.bgg@...il.com> wrote:
>
>
>
> On 14/10/2020 05:06, Nicolas Boichat wrote:
> > On Wed, Oct 14, 2020 at 10:29 AM Wenbin Mei <wenbin.mei@...iatek.com> wrote:
> >>
> >> On Tue, 2020-10-13 at 17:10 +0200, Matthias Brugger wrote:
> >>>
> >>> On 12/10/2020 14:45, Wenbin Mei wrote:
> >>>> MT8192 msdc is an independent sub system, we need control more bus
> >>>> clocks for it.
> >>>> Add support for the additional subsys clocks to allow it to be
> >>>> configured appropriately.
> >>>>
> >>>> Signed-off-by: Wenbin Mei <wenbin.mei@...iatek.com>
[...]
> >>>> +   host->bulk_clks[0].id = "pclk_cg";
> >>>> +   host->bulk_clks[1].id = "axi_cg";
> >>>> +   host->bulk_clks[2].id = "ahb_cg";
> >>>
> >>> That looks at least suspicious. The pointers of id point to some strings defined
> >>> in the function. Aren't they out of scope once msdc_of_clock_parse() has returned?
> >>>
> >> These constants are not in stack range, so they will not be lost.
> >> And I have confirmed it after msdc_of_clock_parse() has returned, these
> >> ids still exist.
> >
> > Yes I guess the constants end up in .rodata (or similar section), but
> > I'm not sure if this is absolutely guaranteed.
> >
> > In any case, this is a commonly used pattern, so I'd hope it's fine
> > (just a sample, there are more):
> > https://elixir.bootlin.com/linux/latest/source/drivers/pci/controller/dwc/pcie-qcom.c#L266
> > https://elixir.bootlin.com/linux/latest/source/sound/soc/codecs/wm8994.c#L4638
> > https://elixir.bootlin.com/linux/latest/source/drivers/mfd/madera-core.c#L467
> > https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpio-dwapb.c#L675
> >
>
> Alright, then this looks good, sorry for the noise!

To close this in more satisfying way, I asked internally, and +Pi-Hsun
Shih digged out this answer:
"""
C11 standard 6.4.5 String literals says: "The multibyte character
sequence is then used to initialize an array of >>static storage
duration<< and length just sufficient to contain the sequence"
"""

> Matthias