diff options
Diffstat (limited to 'drivers/gpu/drm/rcar-du/rcar_du_crtc.c')
| -rw-r--r-- | drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 49 |
1 files changed, 45 insertions, 4 deletions
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c index 6820461f5ed1..c4420538ec85 100644 --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c @@ -125,13 +125,54 @@ 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) + * FDPLL : (fdpll + 1) + * P : 2 + * 2kHz < fvco < 4096MHz + * + * To minimize the jitter, + * N : as large as possible + * M : as small as possible + */ + for (m = 0; m < 4; m++) { + for (n = 119; n > 38; n--) { + /* + * This code only runs on 64-bit architectures, the + * unsigned long type can thus be used for 64-bit + * computation. It will still compile without any + * warning on 32-bit architectures. + * + * To optimize calculations, use fout instead of fvco + * to verify the VCO frequency constraint. + */ + unsigned long fout = input * (n + 1) / (m + 1); + + if (fout < 1000 || fout > 2048 * 1000 * 1000U) + continue; + for (fdpll = 1; fdpll < 32; fdpll++) { unsigned long output; - output = input * (n + 1) / (m + 1) - / (fdpll + 1); + output = fout / (fdpll + 1); if (output >= 400 * 1000 * 1000) continue; |