[PATCH 4/4] drm/i915/intel_dsi: Read back pclk set by GOP and use that as pclk

[Rodrigo Vivi]

On Sat, Jul 07, 2018 at 08:32:16AM +0200, Hans de Goede wrote:
> Hi,
> 
> On 07/06/2018 04:16 PM, Ville Syrjälä wrote:
> > On Tue, Jun 19, 2018 at 10:18:27PM +0200, Hans de Goede wrote:
> > > On BYT and CHT the GOP sometimes initializes the pclk at a (slightly)
> > > different frequency then the pclk which we've calculated.
> > > 
> > > This commit makes the DSI code read-back the pclk set by the GOP and
> > > if that is within a reasonable margin of the calculated pclk, uses
> > > that instead.
> > > 
> > > This fixes the first modeset being a full modeset instead of a
> > > fast modeset on systems where the GOP pclk is different.
> > > 
> > > Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> > > ---
> > >   drivers/gpu/drm/i915/intel_dsi_vbt.c | 14 ++++++++++++++
> > >   1 file changed, 14 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dsi_vbt.c b/drivers/gpu/drm/i915/intel_dsi_vbt.c
> > > index 4d6ffa7b3e7b..d4cc6099012c 100644
> > > --- a/drivers/gpu/drm/i915/intel_dsi_vbt.c
> > > +++ b/drivers/gpu/drm/i915/intel_dsi_vbt.c
> > > @@ -517,6 +517,7 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
> > >   	u32 mul;
> > >   	u16 burst_mode_ratio;
> > >   	enum port port;
> > > +	enum pipe pipe;
> > >   	DRM_DEBUG_KMS("\n");
> > > @@ -583,6 +584,19 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
> > >   	} else
> > >   		burst_mode_ratio = 100;
> > > +	/*
> > > +	 * On BYT / CRC the GOP sometimes picks a slightly different pclk,
> > > +	 * read back the GOP configured pclk and prefer it over ours.
> > > +	 */
> > > +	if ((IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) &&
> > > +	    intel_dsi_get_hw_state(&intel_dsi->base, &pipe)) {
> > > +		u32 gop = intel_dsi_get_pclk(&intel_dsi->base, bpp, NULL);
> > > +
> > > +		DRM_DEBUG_KMS("Calculated pclk %d GOP %d\n", pclk, gop);
> > > +		if (gop >= (pclk * 9 / 10) && gop <= (pclk * 11 / 10))
> > > +			pclk = gop;
> > > +	}
> > 
> > Is the gop acually picking a different clock that what we pick in the
> > end, or is it just that the value in the vbt doesn't quite match what we
> > (and the gop) end up using on account of limitations of the pll?
> 
> I *think* the GOP is picking a different clock, IIRC (*) it is something like
> 90Mhz for the GOP and the VBT says 87Mhz (and our calculations leave it
> unmodified. With this patch which puts pclk at 90Mhz on the specific
> tablet I developed this on, the PLL settings calculated by our PLL code
> end up being exactly the same as the once chosen by the GOP once we have
> the pclk set to 90MHz.
> 
> Note I've seen these small (and sometimes somewhat bigger) differences
> between GOP and VBT pclk on a lot of devices, not just the one tablet
> I developed it on. Since submitting this I've run this on at least
> 5 different CHT/BYT devices and it works as advertised so far.

It seems GOP is just not respecting VBT and using the whatever it judge
the safest option?!

Probably not optimal, but I believe we should stay on the safest side as well,
if this is the case.

> 
> > For that particular problem I think I had patches long ago to go through
> > the pll computation during init so that we basically fix up the slightly
> > bogus clock from the vbt.
> 
> We do end up with a slightly different clock then the 87MHhz when going
> though the PLL calculations, something like 86.33MHz or some such from
> the top of my head, but the problem is not the pclk not matching the
> intel_pipe_config_compare() function does not look at it, it looks at
> dsi_pll.ctrl dsi_pll.div and those don't match, where as they do match
> if we fixup the VBT clock to be the one confgured by the GOP.
> 
> > Any kind of hack that involves reading out the hardware state should go
> > into something like intel_sanitize_encoder(). Actually by that time we
> > have already read out the hw state, so it shouldn't require any
> > modifications to the existing dsi code itself.
> 
> I do not think that intel_sanitize encoder is the right place to do this:
> 
> * I don't want to modify the read-back state, I want to modify our
>   calculated "new/ideal" state to match the read-back state
> * I don't want to directly modify our calculated new/ideal state,
>   instead I want to cleanup / sanitize the values we got from the VBT
>   so that the initial-modeset *and* any future modesets will use the
>   GOP pclk. I believe it is important that if we're going to use the
>   GOP pclk we use it for all modesets consistently.
> * I only want to do this once, at boot when we are sure the mode was
>   set by the GOP and not after suspend/resume when we don't know if the
>   GOP will have touched things or not.
> * It is DSI specific, whereas sofar intel_sanitize_encoder seems to
>   not contain any output specific code.
> 
> Regards,
> 
> Hans
> 
> 
> 
> > 
> > > +
> > >   	intel_dsi->burst_mode_ratio = burst_mode_ratio;
> > >   	intel_dsi->pclk = pclk;
> > > -- 
> > > 2.17.1
> > 
>