From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen-Yu Tsai Subject: Re: [PATCH 09/18] drm/sun4i: tcon: Adjust dotclock dividers range Date: Fri, 14 Jul 2017 12:14:37 +0800 Message-ID: References: <74db696da66cffafe1e729fe2df73b437c8fd483.1499955058.git-series.maxime.ripard@free-electrons.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <74db696da66cffafe1e729fe2df73b437c8fd483.1499955058.git-series.maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Maxime Ripard Cc: Mark Brown , Thierry Reding , Laurent Pinchart , Chen-Yu Tsai , dri-devel , Daniel Vetter , David Airlie , Mark Rutland , Rob Herring , linux-kernel , linux-arm-kernel , devicetree , Boris Brezillon , Thomas Petazzoni List-Id: dri-devel@lists.freedesktop.org On Thu, Jul 13, 2017 at 10:13 PM, Maxime Ripard wrote: > It seems like the dotclock dividers are a bit less strict range, and can > operate even with a smaller than 6 divider. Loose the boundaries a bit. > > Signed-off-by: Maxime Ripard > --- > drivers/gpu/drm/sun4i/sun4i_dotclock.c | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c > index d401156490f3..0b844c0dd102 100644 > --- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c > +++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c > @@ -77,7 +77,25 @@ static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate, > u8 best_div = 1; > int i; > > - for (i = 6; i <= 127; i++) { > + /* > + * There's something odd here. > + * > + * In the A13 user manual, this is stated to be >= 6 when > + * dclk1 and dclk2 are used (without any hint on how to use > + * them), and >= 4 when only dclk is used. You set it in TCON0_IO_POL_REG, which sets the clock phase delay. I think we were setting this before, but you removed it as part of the previous TCON clean up patches? In the A33, there are even more options, like DCLK / 2 (with 0 or 90 degree phase delay). > + * > + * In the A33 user manual, when only dclk is used, it is set > + * to be >= 6 in the former case, and >= 1 in the > + * latter. There's also some (obscure) explanations about the > + * dclk1 and dclk2 vs dclk that seems to be in the upper 4 > + * bits. What those clocks are and what bit does what is not > + * really clear. Looks like mux bits to me. How they differ from TCON0_IO_POL_REG is beyond me ATM. ChenYu > + * > + * On the A33 however, while something lower than 4 works, it > + * does have a few artifacts. Let's not use those values, and > + * see how it goes. > + */ > + for (i = 4; i <= 127; i++) { > unsigned long ideal = rate * i; > unsigned long rounded; > > -- > git-series 0.9.1 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html