Re: [PATCH v3 09/16] reset: starfive-jh7100: Add StarFive JH7100 reset driver

[Emil Renner Berthing <kernel@xxxxxxxx>]

On Tue, 2 Nov 2021 at 22:17, Emil Renner Berthing <kernel@xxxxxxxx> wrote:
> On Tue, 2 Nov 2021 at 21:14, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
> > On Tue, Nov 2, 2021 at 9:59 PM Emil Renner Berthing <kernel@xxxxxxxx> wrote:
> > > On Tue, 2 Nov 2021 at 20:43, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
> > > > On Tue, Nov 2, 2021 at 6:50 PM Emil Renner Berthing <kernel@xxxxxxxx> wrote:
> >
> > ...
> >
> > > > > +/*
> > > > > + * the registers work like a 32bit bitmap, so writing a 1 to the m'th bit of
> > > > > + * the n'th ASSERT register asserts line 32n + m, and writing a 0 deasserts the
> > > > > + * same line.
> > > > > + * most reset lines have their status inverted so a 0 in the STATUS register
> > > > > + * means the line is asserted and a 1 means it's deasserted. a few lines don't
> > > > > + * though, so store the expected value of the status registers when all lines
> > > > > + * are asserted.
> > > > > + */
> > > >
> > > > Besides missing capitalization,
> > >
> > > I'm confused. it was you who wanted all comments to capitalized the same..
> >
> > Yes and there are two types of the comments, one-liners and
> > multi-line. In multi-line you usually use proper English grammar,
> > where capitalization means what it means. For the one-liners just
> > choose either small letters or capital letters to start them with.
>
> That sounds reasonable, it was just that you complained about
> inconsistent comments in the pinctrl driver that follows the above.
>
> > > if it sounds like bitmap, use bitmap.
> > > > I have checked DT definitions and it seems you don't even need the
> > > > BIT_MASK() macro,
> > > >
> > > > > +static const u32 jh7100_reset_asserted[4] = {
> > > > > +       /* STATUS0 register */
> > > > > +       BIT_MASK32(JH7100_RST_U74) |
> > > > > +       BIT_MASK32(JH7100_RST_VP6_DRESET) |
> > > > > +       BIT_MASK32(JH7100_RST_VP6_BRESET),
> > > > > +       /* STATUS1 register */
> > > > > +       BIT_MASK32(JH7100_RST_HIFI4_DRESET) |
> > > > > +       BIT_MASK32(JH7100_RST_HIFI4_BRESET),
> > > > > +       /* STATUS2 register */
> > > > > +       BIT_MASK32(JH7100_RST_E24),
> > > > > +       /* STATUS3 register */
> > > > > +       0,
> > > > > +};
> > > >
> > > > Yury, do we have any clever (clean) way to initialize a bitmap with
> > > > particular bits so that it will be a constant from the beginning? If
> > > > no, any suggestion what we can provide to such users?
> > >
> > > The problem is, that even if we could initialize this without the
> > > monstrosity in our last conversation a 64bit bitmap would still
> > > produce worse code. As it is now it's simply a 32bit load and mask
> > > with index and mask already calculated for the registers. In the
> > > status callback the mask can even be folded into the register read
> > > mask. With a 64bit bitmap you'd need to calculate new 64bit index and
> > > masks, and then conditionally shift the bits into position.
> >
> > Why? You may use 8 byte IO (writeq() / readq() or their relaxed versions), no?
> >
> > > If this reflection of the 32bit registers bothers you that much
> >
> > What bothers me is hidden endianess issues (yeah, here it might be
> > theoretical, but consider that somebody will look at your code and use
> > it as the best example ever).
>
> Wouldn't endian issues be a reason to make sure we read 32bit
> registers with 32bit reads? Or do you expect a hypothetical big-endian
> StarFive SoC to also change the order of the registers?

Hi Andy.

I'd really like to understand your reasoning here. As far as I can
tell reading 2 adjacent 32bit registers with a 64bit read as you're
proposing is exactly what would cause endian issues. Eg. on little
endian you'd get reg0 | reg1 << 32 whereas on big-endian you'd get
reg0 << 32 | reg1.

/Emil