Re: [PATCH] drm/omap: increase DSS5 max tv pclk to 192MHz

[Tomi Valkeinen]

On 09/11/2021 15:33, Neil Armstrong wrote:
> Hi Tomi,
>
> On 12/10/2021 15:39, Neil Armstrong wrote:
> > From: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> >
> > DSS5's maximum tv pclk rate (i.e. HDMI) is set to 186MHz, which comes
> > from the TRM (DPLL_HDMI_CLK1 frequency must be lower than 186 MHz). To
> > support DRA76's wide screen HDMI feature, we need to increase this
> > maximum rate.
> >
> > Testing shows that the PLL seems to work fine even with ~240MHz clocks,
> > and even the HDMI output at that clock is stable enough for monitors to
> > show a picture. This holds true for all DRA7 and AM5 SoCs (and probably
> > also for OMAP5).
> >
> > However, the highest we can go without big refactoring to the clocking
> > code is 192MHz, as that is the DSS func clock we get from the PRCM. So,
> > increase the max HDMI pixel clock to 192MHz for now, to allow some more
> > 2k+ modes to work.
> >
> > This patch never had a clear confirmation from HW people, but this
> > change stayed on production trees for multiple years without any report
> > on an eventual breakage.
> >
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> > Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/omapdrm/dss/dispc.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Tomi,
> >
> > I slighly changed the commit message to point the fact this patch has been
> > used in production fort years without any sign of breakage.
> >
> > Neil
> >
> > diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
> > index 5619420cc2cc..3c4a4991e45a 100644
> > --- a/drivers/gpu/drm/omapdrm/dss/dispc.c
> > +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
> > @@ -4458,7 +4458,7 @@ static const struct dispc_features omap54xx_dispc_feats = {
> >   	.mgr_width_max		=	4096,
> >   	.mgr_height_max		=	4096,
> >   	.max_lcd_pclk		=	170000000,
> > -	.max_tv_pclk		=	186000000,
> > +	.max_tv_pclk		=	192000000,
> >   	.max_downscale		=	4,
> >   	.max_line_width		=	2048,
> >   	.min_pcd		=	1,
> >
> > base-commit: e4e737bb5c170df6135a127739a9e6148ee3da82
>
> Gentle ping,

Thanks, I'll apply this to drm-misc-next.

 Tomi