On Fri, Mar 12, 2021 at 10:55:21AM +0000, Brian Starkey wrote: > (Adding back James again - did you use get_maintainer.pl?) > > On Thu, Mar 11, 2021 at 12:08:46PM +0000, carsten.haitzler@xxxxxxxxxxxx wrote: > > From: Carsten Haitzler <carsten.haitzler@xxxxxxx> > > > > When setting up a readback connector that writes data back to memory > > rather than to an actual output device (HDMI etc.), rounding was set > > to round. As the DPU uses a higher internal number of bits when generating > > a color value, this round-down back to 8bit ended up with everything > > being off-by one. e.g. #fefefe became #ffffff. This sets > > Perhaps overly pedantic, but now we've tracked down what was actually > happening I think we can be more precise here. Not _everything_ is > off-by-one, it's just rounding in the standard sense - if the most > significant bit-to-be-discarded is set, the value is rounded up to > minimise the absolute error introduced by bit-depth reduction. > > > rounding to "round-down" so things end up correct by turning on the LW_TRC > > round down flag. > > Can we call it "truncate" rather than round down? I think it makes > "TRC" a bit more understandable. > > > > > Signed-off-by: Carsten Haitzler <carsten.haitzler@xxxxxxx> > > --- > > drivers/gpu/drm/arm/display/komeda/d71/d71_component.c | 7 ++++++- > > drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h | 1 + > > 2 files changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c b/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c > > index 8a02ade369db..e97acc5519d1 100644 > > --- a/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c > > +++ b/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c > > @@ -468,7 +468,12 @@ static void d71_wb_layer_update(struct komeda_component *c, > > struct komeda_layer_state *st = to_layer_st(state); > > struct drm_connector_state *conn_st = state->wb_conn->state; > > struct komeda_fb *kfb = to_kfb(conn_st->writeback_job->fb); > > - u32 ctrl = L_EN | LW_OFM, mask = L_EN | LW_OFM | LW_TBU_EN; > > + /* LW_TRC sets rounding to truncate not round which is needed for > > + * the output of writeback to match the input in the most common > > + * use cases like RGB888 -> RGB888, so set this bit by default > > + */ > > Hm, not sure why this file uses "net/" style comments, but as you > said, this is in-keeping with the rest of the file, so meh :-) > > > + u32 ctrl = LW_TRC | L_EN | LW_OFM; > > + u32 mask = LW_TRC | L_EN | LW_OFM | LW_TBU_EN; > > If you were aiming for matching register order, this should be: > > L_EN | LW_TRC | LW_OFM | LW_TBU_EN > > > I think it'd be nice to have the exact behaviour in the commit > message, but either way this seems OK as a pragmatic fix so: > > Reviewed-by: Brian Starkey <brian.starkey@xxxxxxx> > > Thanks, > -Brian > > > u32 __iomem *reg = c->reg; > > > > d71_layer_update_fb(c, kfb, st->addr); > > diff --git a/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h b/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h > > index e80172a0b320..a8036689d721 100644 > > --- a/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h > > +++ b/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h > > @@ -321,6 +321,7 @@ > > #define LAYER_WR_FORMAT 0x0D8 > > > > /* Layer_WR control bits */ > > +#define LW_TRC BIT(1) > > #define LW_OFM BIT(4) > > #define LW_LALPHA(x) (((x) & 0xFF) << 8) > > #define LW_A_WCACHE(x) (((x) & 0xF) << 28) > > -- > > 2.30.0 > > Acked-by: James Qian Wang <james.qian.wang@xxxxxxx> Thanks James > > _______________________________________________ > > dri-devel mailing list > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > https://lists.freedesktop.org/mailman/listinfo/dri-devel _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
