sunxi: dram: Configurable MBUS clock speed (use PLL5 or PLL6)

The sun5i hardware (Allwinner A13) introduced configurable MBUS clock
speed. Allwinner A13 uses only 16-bit data bus width to connect the
external DRAM, which is halved compared to the 32-bit data bus of sun4i
(Allwinner A10), so it does not make much sense to clock a wider
internal bus at a very high speed. The Allwinner A13 manual specifies
300 MHz MBUS clock speed limit and 533 MHz DRAM clock speed limit. Newer
sun7i hardware (Allwinner A20) has a full width 32-bit external memory
interface again, but still keeps the MBUS clock speed configurable.
Clocking MBUS too low inhibits memory performance and one has to find
the optimal MBUS/DRAM clock speed ratio, which may depend on many
factors:
    http://linux-sunxi.org/A10_DRAM_Controller_Performance

This patch introduces a new 'mbus_clock' parameter for the 'dram_para'
struct and uses it as a desired MBUS clock speed target. If 'mbus_clock'
is not set, 300 MHz is used by default to match the older hardcoded
settings.

PLL5P and PLL6 are both evaluated as possible clock sources. Preferring
the one, which can provide higher clock frequency that is lower or
equal to the 'mbus_clock' target. In the case of a tie, PLL5P has
higher priority.

Attempting to set the MBUS clock speed has no effect on sun4i, but does
no harm either.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

arch/arm/cpu/armv7/sunxi/dram.c

@@ -235,11 +235,20 @@ static void mctl_configure_hostport(void)
 		writel(hpcr_value[i], &dram->hpcr[i]);
 }
 
-static void mctl_setup_dram_clock(u32 clk)
+static void mctl_setup_dram_clock(u32 clk, u32 mbus_clk)
 {
 	u32 reg_val;
 	struct sunxi_ccm_reg *ccm = (struct sunxi_ccm_reg *)SUNXI_CCM_BASE;
 
+	/* PLL5P and PLL6 are the potential clock sources for MBUS */
+	u32 pll6x_div, pll5p_div;
+	u32 pll6x_clk = clock_get_pll6() / 1000000;
+	u32 pll5p_clk = clk / 24 * 24;
+	u32 pll5p_rate, pll6x_rate;
+#ifdef CONFIG_SUN7I
+	pll6x_clk *= 2; /* sun7i uses PLL6*2, sun5i uses just PLL6 */
+#endif
+
 	/* setup DRAM PLL */
 	reg_val = readl(&ccm->pll5_cfg);
 	reg_val &= ~CCM_PLL5_CTRL_M_MASK;		/* set M to 0 (x1) */
@@ -248,30 +257,35 @@ static void mctl_setup_dram_clock(u32 clk)
 	reg_val &= ~CCM_PLL5_CTRL_P_MASK;		/* set P to 0 (x1) */
 	if (clk >= 540 && clk < 552) {
 		/* dram = 540MHz, pll5p = 540MHz */
+		pll5p_clk = 540;
 		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
 		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
 		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(15));
 		reg_val |= CCM_PLL5_CTRL_P(1);
 	} else if (clk >= 512 && clk < 528) {
 		/* dram = 512MHz, pll5p = 384MHz */
+		pll5p_clk = 384;
 		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(3));
 		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(4));
 		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(16));
 		reg_val |= CCM_PLL5_CTRL_P(2);
 	} else if (clk >= 496 && clk < 504) {
 		/* dram = 496MHz, pll5p = 372MHz */
+		pll5p_clk = 372;
 		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(3));
 		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(2));
 		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(31));
 		reg_val |= CCM_PLL5_CTRL_P(2);
 	} else if (clk >= 468 && clk < 480) {
 		/* dram = 468MHz, pll5p = 468MHz */
+		pll5p_clk = 468;
 		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
 		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
 		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(13));
 		reg_val |= CCM_PLL5_CTRL_P(1);
 	} else if (clk >= 396 && clk < 408) {
 		/* dram = 396MHz, pll5p = 396MHz */
+		pll5p_clk = 396;
 		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
 		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
 		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(11));
@@ -298,20 +312,30 @@ static void mctl_setup_dram_clock(u32 clk)
 	clrbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_GPS);
 #endif
 
-#if defined(CONFIG_SUN5I) || defined(CONFIG_SUN7I)
 	/* setup MBUS clock */
-	reg_val = CCM_MBUS_CTRL_GATE |
-#ifdef CONFIG_SUN7I
-		  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL6) |
-		  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(2)) |
-		  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(2));
-#else /* defined(CONFIG_SUN5I) */
-		  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL5) |
-		  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(1)) |
-		  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(2));
-#endif
+	if (!mbus_clk)
+		mbus_clk = 300;
+	pll6x_div = DIV_ROUND_UP(pll6x_clk, mbus_clk);
+	pll5p_div = DIV_ROUND_UP(pll5p_clk, mbus_clk);
+	pll6x_rate = pll6x_clk / pll6x_div;
+	pll5p_rate = pll5p_clk / pll5p_div;
+
+	if (pll6x_div <= 16 && pll6x_rate > pll5p_rate) {
+		/* use PLL6 as the MBUS clock source */
+		reg_val = CCM_MBUS_CTRL_GATE |
+			  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL6) |
+			  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(1)) |
+			  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(pll6x_div));
+	} else if (pll5p_div <= 16) {
+		/* use PLL5P as the MBUS clock source */
+		reg_val = CCM_MBUS_CTRL_GATE |
+			  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL5) |
+			  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(1)) |
+			  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(pll5p_div));
+	} else {
+		panic("Bad mbus_clk\n");
+	}
 	writel(reg_val, &ccm->mbus_clk_cfg);
-#endif
 
 	/*
 	 * open DRAMC AHB & DLL register clock
@@ -511,7 +535,7 @@ unsigned long dramc_init(struct dram_para *para)
 		return 0;
 
 	/* setup DRAM relative clock */
-	mctl_setup_dram_clock(para->clock);
+	mctl_setup_dram_clock(para->clock, para->mbus_clock);
 
 	/* Disable any pad power save control */
 	mctl_disable_power_save();

arch/arm/include/asm/arch-sunxi/dram.h

@@ -69,6 +69,7 @@ struct sunxi_dram_reg {
 
 struct dram_para {
 	u32 clock;
+	u32 mbus_clock;
 	u32 type;
 	u32 rank_num;
 	u32 density;