New patch to review for coreboot: nb/gm45/gma.c: use linux code to compute LVDS dotclock divisors
Arthur Heymans (arthur@aheymans.xyz) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/16741
-gerrit
commit 5ddd32fd72f2c4fdb83e34bc586758a012e352ec Author: Arthur Heymans arthur@aheymans.xyz Date: Mon Sep 26 08:44:46 2016 +0200
nb/gm45/gma.c: use linux code to compute LVDS dotclock divisors
This reuses linux code (at least 4.1) to compute the graphic clock divisors for LVDS displays on the gm45 northbridge. The divisors m1, m2, n, p1, p2 need to be such that "BASE_FREQUECY * (5 * (m1 + 2) + (m2 + 2)) / (n + 2) / (p1 * p2)" is as close as possible to the target_frequency. On g4x hardware the BASE_FREQUENCY is 96000kHz.
This potentially increases LVDS display compatibibility.
Change-Id: I2323af5756431e89769f95059790f5a922af14b4 Signed-off-by: Arthur Heymans arthur@aheymans.xyz --- src/northbridge/intel/gm45/gma.c | 70 +++++++++++++++++++--------------------- 1 file changed, 33 insertions(+), 37 deletions(-)
diff --git a/src/northbridge/intel/gm45/gma.c b/src/northbridge/intel/gm45/gma.c index 14f695e..cd9946e 100644 --- a/src/northbridge/intel/gm45/gma.c +++ b/src/northbridge/intel/gm45/gma.c @@ -61,13 +61,13 @@ static void gma_init_lvds(const struct northbridge_intel_gm45_config *info, u32 hactive, vactive, right_border, bottom_border; int hpolarity, vpolarity; u32 vsync, hsync, vblank, hblank, hfront_porch, vfront_porch; - u32 candp1, candn; - u32 best_delta = 0xffffffff; + u32 smallest_err = 0xffffffff; u32 target_frequency; u32 pixel_p1 = 1; u32 pixel_n = 1; u32 pixel_m1 = 1; u32 pixel_m2 = 1; + u32 pixel_p2; u32 link_frequency = info->gfx.link_frequency_270_mhz ? 270000 : 162000; u32 data_m1; u32 data_n1 = 0x00800000; @@ -120,8 +120,6 @@ static void gma_init_lvds(const struct northbridge_intel_gm45_config *info, hfront_porch = mode->hso; vfront_porch = mode->vso;
- target_frequency = mode->lvds_dual_channel ? mode->pixel_clock - : (2 * mode->pixel_clock); if (IS_ENABLED(CONFIG_FRAMEBUFFER_KEEP_VESA_MODE)) { vga_sr_write(1, 1); vga_sr_write(0x2, 0xf); @@ -150,40 +148,38 @@ static void gma_init_lvds(const struct northbridge_intel_gm45_config *info, vga_textmode_init(); }
- /* Find suitable divisors. */ - for (candp1 = 1; candp1 <= 8; candp1++) { - for (candn = 5; candn <= 10; candn++) { - u32 cur_frequency; - u32 m; /* 77 - 131. */ - u32 denom; /* 35 - 560. */ - u32 current_delta; - - denom = candn * candp1 * 7; - /* Doesnt overflow for up to - 5000000 kHz = 5 GHz. */ - m = (target_frequency * denom + 60000) / 120000; - - if (m < 77 || m > 131) - continue; - - cur_frequency = (120000 * m) / denom; - if (target_frequency > cur_frequency) - current_delta = target_frequency - cur_frequency; - else - current_delta = cur_frequency - target_frequency; - + target_frequency = mode->pixel_clock; + /* p2 divisor must 7 for dual channel LVDS */ + /* and 14 for single channel LVDS */ + pixel_p2 = mode->lvds_dual_channel ? 7 : 14;
- if (best_delta > current_delta) { - best_delta = current_delta; - pixel_n = candn; - pixel_p1 = candp1; - pixel_m2 = ((m + 3) % 5) + 7; - pixel_m1 = (m - pixel_m2) / 5; + /* Find suitable divisors, m1, m2, p1, n. */ + /* refclock * (5 * (m1 + 2) + (m1 + 2)) / (n + 2) / p1 / p2 */ + /* should be closest to target frequency as possible */ + u32 candn, candm1, candm2, candp1; + for (candn = 1; candn <= 3; candn++) { + for (candm1 = 23; candm1 >= 17; candm1--) { + for (candm2 = 11; candm2 >= 5; candm2--) { + for (candp1 = mode->lvds_dual_channel ? 6 : 8; + candp1 >= 2; candp1--) { + u32 m = 5 * (candm1 + 2) + (candm2 + 2); + u32 p = candp1 * pixel_p2; + u32 vco = DIV_ROUND_CLOSEST(BASE_FREQUECY * m, candn + 2); + u32 dot = DIV_ROUND_CLOSEST(vco, p); + u32 this_err = ABS(dot - target_frequency); + if (this_err < smallest_err) { + smallest_err = this_err; + pixel_n = candn; + pixel_m1 = candm1; + pixel_m2 = candm2; + pixel_p1 = candp1; + } + } } } }
- if (best_delta == 0xffffffff) { + if (smallest_err == 0xffffffff) { printk (BIOS_ERR, "Couldn't find GFX clock divisors\n"); return; } @@ -217,8 +213,8 @@ static void gma_init_lvds(const struct northbridge_intel_gm45_config *info, printk(BIOS_DEBUG, "Pixel N=%d, M1=%d, M2=%d, P1=%d\n", pixel_n, pixel_m1, pixel_m2, pixel_p1); printk(BIOS_DEBUG, "Pixel clock %d kHz\n", - 120000 * (5 * pixel_m1 + pixel_m2) / pixel_n - / (pixel_p1 * 7)); + BASE_FREQUECY * (5 * (pixel_m1 + 2) + (pixel_m2 + 2) + / (pixel_n + 2) / (pixel_p1 * pixel_p2)));
write32(mmio + LVDS, (hpolarity << 20) | (vpolarity << 21) @@ -231,8 +227,8 @@ static void gma_init_lvds(const struct northbridge_intel_gm45_config *info, write32(mmio + PP_CONTROL, PANEL_UNLOCK_REGS | (read32(mmio + PP_CONTROL) & ~PANEL_UNLOCK_MASK)); write32(mmio + FP0(0), - ((pixel_n - 2) << 16) - | ((pixel_m1 - 2) << 8) | (pixel_m2 - 2)); + (pixel_n << 16) + | (pixel_m1 << 8) | (pixel_m2)); write32(mmio + DPLL(0), DPLL_VCO_ENABLE | DPLLB_MODE_LVDS | DPLL_VGA_MODE_DIS
-
Arthur Heymans