Hi Marek,
On Wed, 31 Dec 2025 at 15:57, Marek Vasut
<[email protected]> wrote:
> Currently, in rcar_mipi_dsi_parameters_calc(), the VCLK divider is stored
> in setup_info structure as BIT(divider). The rcar_mipi_dsi_parameters_calc()
> is called at the early beginning of rcar_mipi_dsi_startup() function. Later,
> in the same rcar_mipi_dsi_startup() function, the stored BIT(divider) value
> is passed to __ffs() to calculate back the divider out of the value again.
>
> Factor out VCLK divider calculation into rcar_mipi_dsi_vclk_divider()
> function and call the function from both rcar_mipi_dsi_parameters_calc()
> and rcar_mipi_dsi_startup() to avoid this back and forth BIT() and _ffs()
> and avoid unnecessarily storing the divider value in setup_info at all.
>
> This rework has a slight side-effect, in that it should allow the compiler
> to better evaluate the code and avoid compiler warnings about variable
> value overflows, which can never happen.
>
> Reported-by: kernel test robot <[email protected]>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Closes:
> https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Signed-off-by: Marek Vasut <[email protected]>
Thanks for your patch!
> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> @@ -412,18 +427,20 @@ static void rcar_mipi_dsi_parameters_calc(struct
> rcar_mipi_dsi *dsi,
>
> fin_rate = clk_get_rate(clk);
>
> + div = rcar_mipi_dsi_vclk_divider(dsi, setup_info);
> +
> switch (dsi->info->model) {
> case RCAR_DSI_V3U:
> default:
> - setup_info->vclk_divider = 1 << ((clk_cfg->vco_cntrl >> 4) &
> 0x3);
> + vclk_divider = BIT_U32(div);
BIT_U16(), as vclk_divider is u16?
> break;
>
> case RCAR_DSI_V4H:
> - setup_info->vclk_divider = 1 << (((clk_cfg->vco_cntrl >> 3) &
> 0x7) + 1);
> + vclk_divider = BIT_U32(div + 1);
Likewise.
> break;
> }
>
> - rcar_mipi_dsi_pll_calc(dsi, fin_rate, fout_target, setup_info);
> + rcar_mipi_dsi_pll_calc(dsi, fin_rate, fout_target, setup_info,
> vclk_divider);
>
> /* Find hsfreqrange */
> setup_info->hsfreq = setup_info->fout * 2;
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
