linux-kernel - Re: [PATCH v3 07/42] soc: Add SoC driver for Cirrus ep93xx

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Message-ID: <CAHp75VccVh+M444AAixVzSvM6-FsDm8jDYdakHhNFTAL8WOGMA@mail.gmail.com>
Date:   Mon, 13 Nov 2023 12:19:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexander Sverdlin <alexander.sverdlin@...il.com>
Cc:     Andy Shevchenko <andy@...nel.org>, nikita.shubin@...uefel.me,
        Hartley Sweeten <hsweeten@...ionengravers.com>,
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Subject: Re: [PATCH v3 07/42] soc: Add SoC driver for Cirrus ep93xx

On Sat, Nov 11, 2023 at 11:33 PM Alexander Sverdlin
<alexander.sverdlin@...il.com> wrote:
> On Fri, 2023-07-21 at 17:13 +0300, Andy Shevchenko wrote:

...

> > > +       spin_lock_irqsave(&ep93xx_swlock, flags);
> > > +
> > > +       regmap_read(map, EP93XX_SYSCON_DEVCFG, &val);
> > > +       val &= ~clear_bits;
> > > +       val |= set_bits;
> > > +       regmap_write(map, EP93XX_SYSCON_SWLOCK, EP93XX_SWLOCK_MAGICK);
> > > +       regmap_write(map, EP93XX_SYSCON_DEVCFG, val);
> >
> > Is this sequence a must?
> > I.o.w. can you first supply magic and then update devcfg?
> >
> > > +       spin_unlock_irqrestore(&ep93xx_swlock, flags);

...

> > > +void ep93xx_swlocked_update_bits(struct regmap *map, unsigned int reg,
> > > +                                unsigned int mask, unsigned int val)

> > Same Q as above.
>
> EP93xx User Manual [1] has most verbose description of SWLock for ADC
> block:
> "Writing 0xAA to this register will unlock all locked registers until the
> next block access. The ARM lock instruction prefix should be used for the
> two consequtive write cycles when writing to locked chip registers."
>
> One may conclude that RmW (two accesses to the particular block) sequence
> is not appropriate.

It's not obvious to me. The terms "block access" and "block cycle"
occur only once in the very same section that describes ADCSWLock. The
meaning of these terms is not fully understandable. So, assuming that
you have tried it differently and it indeed doesn't work, let's go
with this one.

> [1] https://cdn.embeddedts.com/resource-attachments/ts-7000_ep9301-ug.pdf



--
With Best Regards,
Andy Shevchenko