On Mon, Apr 04, 2022 at 04:49:18PM +0300, Vinod Govindapillai wrote: > In configurations with single DRAM channel, for usecases like > 4K 60 Hz, FIFO underruns are observed quite frequently. Looks > like the wm0 watermark values need to bumped up because the wm0 > memory latency calculations are probably not taking the DRAM > channel's impact into account. > > As per the Bspec 49325, if the ddb allocation can hold at least > one plane_blocks_per_line we should have selected method2. > Assuming that modern HW versions have enough dbuf to hold > at least one line, set the wm blocks to equivalent to blocks > per line. > > cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > cc: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> > > Signed-off-by: Vinod Govindapillai <vinod.govindapillai@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_pm.c | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c > index 8824f269e5f5..ae28a8c63ca4 100644 > --- a/drivers/gpu/drm/i915/intel_pm.c > +++ b/drivers/gpu/drm/i915/intel_pm.c > @@ -5474,7 +5474,24 @@ static void skl_compute_plane_wm(const struct intel_crtc_state *crtc_state, > } > } > > - blocks = fixed16_to_u32_round_up(selected_result) + 1; > + /* > + * Lets have blocks at minimum equivalent to plane_blocks_per_line > + * as there will be at minimum one line for lines configuration. > + * > + * As per the Bspec 49325, if the ddb allocation can hold at least > + * one plane_blocks_per_line, we should have selected method2 in > + * the above logic. Assuming that modern versions have enough dbuf > + * and method2 guarantees blocks equivalent to at least 1 line, > + * select the blocks as plane_blocks_per_line. > + * > + * TODO: Revisit the logic when we have better understanding on DRAM > + * channels' impact on the level 0 memory latency and the relevant > + * wm calculations. > + */ > + blocks = skl_wm_has_lines(dev_priv, level) ? > + max_t(u32, fixed16_to_u32_round_up(selected_result) + 1, > + fixed16_to_u32_round_up(wp->plane_blocks_per_line)) : > + fixed16_to_u32_round_up(selected_result) + 1; > lines = div_round_up_fixed16(selected_result, > wp->plane_blocks_per_line); I think this is a good fix, no IGT/BAT regressions are visible, also it fixes some of the current issues at customer side. So don't see any reason for it not to be merged. Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> P.S: there is some checkpatch warning, which probably needs to be addressed :) Stan > > -- > 2.25.1 >
