| Message ID | 871skhssjt.wl%kuninori.morimoto.gx@renesas.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi I noticed 1 typo, 1 bug on this patch. I will post v2 patch > From: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com> > > In general, PLL has VCO (= Voltage controlled oscillator), > one of the very important electronic feature called as "jitter" > is related to this VCO. > In academic generalism, VCO should be maximum to be more small jitter. > In high frequency clock, jitter will be large impact. > Thus, selecting Hi VCO is general theory. > > fin fvco fout fclkout > in --> [1/M] --> |PD| -> [LPF] -> [VCO] -> [1/P] -+-> [1/FDPLL] -> out > +-> | | | > | | > +-----------------[1/N]<-------------+ > > fclkout = fvco / P / FDPLL -- (1) > > In PD, it will loop until fin/M = fvco/P/N > > fvco = fin * P * N / M -- (2) > > (1) + (2) indicates, fclkout = fin * N / M / FDPLL > In this device, N = (n + 1), M = (m + 1), P = 2, thus > > fout = fin * (n + 1) / (m + 1) / FDPLL > > This is the datasheet formula. > One note here is that it should be 2000 < fvco < 4096MHz > To be smaller jitter, fvco should be maximum, > in other words, N as large as possible, M as small as possible driver > should select. Here, basically M=1. > This patch do it. > > Reported-by: HIROSHI INOSE <hiroshi.inose.rb@renesas.com> > Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com> > --- > drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 36 ++++++++++++++++++++++++++++++++-- > 1 file changed, 34 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c > index b492063..45540fe 100644 > --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c > +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c > @@ -125,8 +125,40 @@ static void rcar_du_dpll_divider(struct rcar_du_crtc *rcrtc, > unsigned int m; > unsigned int n; > > - for (n = 39; n < 120; n++) { > - for (m = 0; m < 4; m++) { > + /* > + * fin fvco fout fclkout > + * in --> [1/M] --> |PD| -> [LPF] -> [VCO] -> [1/P] -+-> [1/FDPLL] -> out > + * +-> | | | > + * | | > + * +-----------------[1/N]<-------------+ > + * > + * fclkout = fvco / P / FDPLL -- (1) > + * > + * fin/M = fvco/P/N > + * > + * fvco = fin * P * N / M -- (2) > + * > + * (1) + (2) indicates > + * > + * fclkout = fin * N / M / FDPLL > + * > + * NOTES > + * N = (n + 1), M = (m + 1), P = 2 > + * 2000 < fvco < 4096Mhz > + * Basically M=1 > + * > + * To be small jitter, > + * N : as large as possible > + * M : as small as possible > + */ > + for (m = 0; m < 4; m++) { > + for (n = 119; n > 40; n--) { > + unsigned long long fvco = input * 2 * (n + 1) / (m + 1); > + > + if ((fvco < 2000) || > + (fvco > 4096000000ll)) > + continue; > + > for (fdpll = 1; fdpll < 32; fdpll++) { > unsigned long output; > > -- > 1.9.1 >
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c index b492063..45540fe 100644 --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c @@ -125,8 +125,40 @@ static void rcar_du_dpll_divider(struct rcar_du_crtc *rcrtc, unsigned int m; unsigned int n; - for (n = 39; n < 120; n++) { - for (m = 0; m < 4; m++) { + /* + * fin fvco fout fclkout + * in --> [1/M] --> |PD| -> [LPF] -> [VCO] -> [1/P] -+-> [1/FDPLL] -> out + * +-> | | | + * | | + * +-----------------[1/N]<-------------+ + * + * fclkout = fvco / P / FDPLL -- (1) + * + * fin/M = fvco/P/N + * + * fvco = fin * P * N / M -- (2) + * + * (1) + (2) indicates + * + * fclkout = fin * N / M / FDPLL + * + * NOTES + * N = (n + 1), M = (m + 1), P = 2 + * 2000 < fvco < 4096Mhz + * Basically M=1 + * + * To be small jitter, + * N : as large as possible + * M : as small as possible + */ + for (m = 0; m < 4; m++) { + for (n = 119; n > 40; n--) { + unsigned long long fvco = input * 2 * (n + 1) / (m + 1); + + if ((fvco < 2000) || + (fvco > 4096000000ll)) + continue; + for (fdpll = 1; fdpll < 32; fdpll++) { unsigned long output;