[PATCH 3/6] drm: rcar-du: Fix LVDS stop sequence

[Laurent Pinchart]

Hi Tomi,

On Thu, Jan 19, 2023 at 10:49:28AM +0200, Tomi Valkeinen wrote:
> On 18/01/2023 23:12, Laurent Pinchart wrote:
> > On Tue, Jan 17, 2023 at 03:51:51PM +0200, Tomi Valkeinen wrote:
> >> From: Koji Matsuoka <koji.matsuoka.xm at renesas.com>
> >>
> >> According to H/W manual, LVDCR0 register must be cleared bit by bit when
> > 
> > s at H/W at the hardware/
> > 
> >> disabling LVDS.
> > 
> > I don't like this much, but I think I'll stop fighting :-)
> > 
> >> Signed-off-by: Koji Matsuoka <koji.matsuoka.xm at renesas.com>
> >> Signed-off-by: LUU HOAI <hoai.luu.ub at renesas.com>
> >> [tomi.valkeinen: simplified the code a bit]
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas at ideasonboard.com>
> >> ---
> >>   drivers/gpu/drm/rcar-du/rcar_lvds.c | 27 ++++++++++++++++++++++++++-
> >>   1 file changed, 26 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> >> index 674b727cdaa2..01800cef1c33 100644
> >> --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
> >> +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> >> @@ -87,6 +87,11 @@ static void rcar_lvds_write(struct rcar_lvds *lvds, u32 reg, u32 data)
> >>   	iowrite32(data, lvds->mmio + reg);
> >>   }
> >>   
> >> +static u32 rcar_lvds_read(struct rcar_lvds *lvds, u32 reg)
> >> +{
> >> +	return ioread32(lvds->mmio + reg);
> >> +}
> > 
> > Could you please move read before write ?
> 
> Sure.
> 
> >> +
> >>   /* -----------------------------------------------------------------------------
> >>    * PLL Setup
> >>    */
> >> @@ -549,8 +554,28 @@ 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);
> >> +	}
> > 
> > This will leave LVDCR0_BEN and LVDCR0_LVEN on Gen2. Is that fine ?
> 
> I don't know, I don't have the manuals or HW. But your point is a bit 
> worrying.
> 
> I think we can just do a rcar_lvds_write(lvds, LVDCR0, 0) after the 
> above shenanigans, to make sure everything is disabled. The HW manual 
> doesn't tell us to do that, though, on gen3. Do you think that will be a 
> problem?
> 
> And I'm not fully serious with the last sentence...

:-)

A write(lvds, LVDCR0, 0) should fix it, I'm fine with that.

-- 
Regards,

Laurent Pinchart