Hi Tomi,
On Wed, 29 Oct 2025 at 11:37, Tomi Valkeinen
<[email protected]> wrote:
> On 29/10/2025 11:57, Geert Uytterhoeven wrote:
> > On Tue, 28 Oct 2025 at 18:15, Tomi Valkeinen
> > <[email protected]> wrote:
> >> On 05/10/2025 06:02, Marek Vasut wrote:
> >>> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
> >>> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
> >>> @@ -246,14 +246,14 @@
> >>>
> >>> #define VCLKSET 0x100c
> >>> #define VCLKSET_CKEN (1 << 16)
> >>> -#define VCLKSET_COLOR_RGB (0 << 8)
> >>> -#define VCLKSET_COLOR_YCC (1 << 8)
> >>> +#define VCLKSET_COLOR_YCC (1 << 8) /* 0:RGB 1:YCbCr */
> >>> #define VCLKSET_DIV_V3U(x) (((x) & 0x3) << 4)
> >>> #define VCLKSET_DIV_V4H(x) (((x) & 0x7) << 4)
> >>> -#define VCLKSET_BPP_16 (0 << 2)
> >>> -#define VCLKSET_BPP_18 (1 << 2)
> >>> -#define VCLKSET_BPP_18L (2 << 2)
> >>> -#define VCLKSET_BPP_24 (3 << 2)
> >>> +#define VCLKSET_BPP_MASK (3 << 2)
> >>> +#define VCLKSET_BPP_16
> >>> FIELD_PREP(VCLKSET_BPP_MASK, 0)
> >>> +#define VCLKSET_BPP_18
> >>> FIELD_PREP(VCLKSET_BPP_MASK, 1)
> >>> +#define VCLKSET_BPP_18L
> >>> FIELD_PREP(VCLKSET_BPP_MASK, 2)
> >>> +#define VCLKSET_BPP_24
> >>> FIELD_PREP(VCLKSET_BPP_MASK, 3)
> >>> #define VCLKSET_LANE(x) (((x) & 0x3) << 0)
> >> It probably doesn't matter, but just wanted to mention: here FIELD_PREP
> >> is used with, e.g., (3 << 2). GENMASK returns an unsigned value, whereas
> >> (3 << 2) is signed.
> >
> > Huh?
> >
> > Either you use the unshifted value "(define for) 3" with FIELD_PREP(),
> > or you use the shifted value "(define for) (3 << 2)" without FIELD_PREP()?
> Sure. My point was, VCLKSET_BPP_MASK is a signed value, but GENMASK()
> would produce an unsigned value. Normally FIELD_PREP() is used with
> GENMASK, i.e. with unsigned mask, but here FIELD_PREP is used with a
> signed mask. Does it matter? I don't know, most likely not.
IC. Yes, it is better to use GENMASK(3, 2) here.
Always use BIT() and GENMASK() for bit definitions.
Or the new BIT_U{8,16,32,64} and GENMASK_U{8,16,32,64,128} if you
want to be really explicit, or avoid compiler warnings when using
~mask later.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
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
