Re: [PATCH v3 4/7] drm: rcar-du: lvds: Fix stop sequence

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Geert,

On Mon, Jan 23, 2023 at 03:28:08PM +0100, Geert Uytterhoeven wrote:
> On Mon, Jan 23, 2023 at 11:48 AM Tomi Valkeinen wrote:
> > From: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
> >
> > According to hardware manual, LVDCR0 register must be cleared bit by bit
> > when disabling LVDS.
> >
> > Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
> > Signed-off-by: LUU HOAI <hoai.luu.ub@renesas.com>
> > [tomi.valkeinen: simplified the code a bit]
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> Thanks for your patch!
> 
> > @@ -544,6 +549,27 @@ static void rcar_lvds_atomic_disable(struct drm_bridge *bridge,
> >                                      struct drm_bridge_state *old_bridge_state)
> >  {
> >         struct rcar_lvds *lvds = bridge_to_rcar_lvds(bridge);
> > +       u32 lvdcr0;
> > +
> > +       lvdcr0 = rcar_lvds_read(lvds, LVDCR0);
> > +
> > +       lvdcr0 &= ~LVDCR0_LVRES;
> > +       rcar_lvds_write(lvds, LVDCR0, lvdcr0);
> > +
> > +       if (lvds->info->quirks & RCAR_LVDS_QUIRK_GEN3_LVEN) {
> > +               lvdcr0 &= ~LVDCR0_LVEN;
> > +               rcar_lvds_write(lvds, LVDCR0, lvdcr0);
> > +       }
> > +
> > +       if (lvds->info->quirks & RCAR_LVDS_QUIRK_PWD) {
> > +               lvdcr0 &= ~LVDCR0_PWD;
> > +               rcar_lvds_write(lvds, LVDCR0, lvdcr0);
> > +       }
> > +
> > +       if (!(lvds->info->quirks & RCAR_LVDS_QUIRK_EXT_PLL)) {
> > +               lvdcr0 &= ~LVDCR0_PLLON;
> > +               rcar_lvds_write(lvds, LVDCR0, lvdcr0);
> > +       }
> 
> Please add a comment explaining why there are multiple register writes,
> to avoid an over-zealous janitor "optimizing" the code later.

I'll add this comment at the top of the function:

        /*
         * Clear the LVDCR0 bits in the order specified by the hardware
         * documentation, ending with a write of 0 to the full register to
         * clear all remaining bits.
         */

> >
> >         rcar_lvds_write(lvds, LVDCR0, 0);
> >         rcar_lvds_write(lvds, LVDCR1, 0);

-- 
Regards,

Laurent Pinchart