[PATCH 1/4] drm/rcar-du: dsi: Convert register bits to BIT() macro

[Geert Uytterhoeven]

On Tue, 12 Aug 2025 at 22:05, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
> On Tue, Aug 12, 2025 at 09:32:36PM +0200, Marek Vasut wrote:
> > On 8/12/25 3:26 PM, Tomi Valkeinen wrote:
> > >> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
> > >> index a6b276f1d6ee..b3e57217ae63 100644
> > >> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
> > >> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
> >
> > [...]
> >
> > >> @@ -51,11 +51,11 @@
> > >>
> > >>   #define TXVMVPRMSET0R                    0x1d0
> > >>   #define TXVMVPRMSET0R_HSPOL_HIG          (0 << 17)
> > >> -#define TXVMVPRMSET0R_HSPOL_LOW           (1 << 17)
> > >> +#define TXVMVPRMSET0R_HSPOL_LOW           BIT(17)
> > >
> > > I'm not sure about this (and below). We have two defines for the HSPOL,
> > > high and low. If one of them is (x << y), shouldn't the other one be of
> > > that style too?
> >
> > It is inconsistent, but one macro describes bit set to 0 and the other
> > bit set to 1 (i.e. the actual bit) which is converted to BIT(n) macro. I
> > would be tempted to remove the bits set to 0, that's probably the real
> > discussion that should happen here. But that would also be a much bigger
> > patch. What do you think ?
>
> For what it's worth, for single-bit register fields, I usually define a
> single macro. I understand it's usually a coding style preference.

An alternative would be to define 3 macros:

    #define TXVMVPRMSET0R_HSPOL        BIT(17)
    #define TXVMVPRMSET0R_HSPOL_HIG    0
    #define TXVMVPRMSET0R_HSPOL_LOW    1

and use FIELD_PREP(TXVMVPRMSET0R_HSPOL, TXVMVPRMSET0R_HSPOL_{HIG,LOW}).
But I agree a single definition is fine for a single-bit register field.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds