The DRAM controller allows to configure impedance either by using the calibration against an external high precision 240 ohm resistor, or by skipping the calibration and loading pre-defined data. The DRAM controller register guide is available here:
http://linux-sunxi.org/A10_DRAM_Controller_Register_Guide#SDR_ZQCR0
The new code supports both of the impedance configuration modes: - If the higher bits of the 'zq' parameter in the 'dram_para' struct are zero, then the lowest 8 bits are used as the ZPROG value, where two divisors encoded in lower and higher 4 bits. One divisor is used for calibrating the termination impedance, and another is used for the output impedance. - If bits 27:8 in the 'zq' parameters are non-zero, then they are used as the pre-defined ZDATA value instead of performing the ZQ calibration.
Two lowest bits in the 'odt_en' parameter enable ODT for the DQ and DQS lines individually. Enabling ODT for both DQ and DQS means that the 'odt_en' parameter needs to be set to 3.
Signed-off-by: Siarhei Siamashka siarhei.siamashka@gmail.com --- Changes for v2: - this is the last part half of the old patch [PATCH 05/14] "sunxi: dram: Code cleanup for the impedance calibration", split as agreed with Ian Campbell. - new commit message now explains how the code works - more comments are added to the code
arch/arm/cpu/armv7/sunxi/dram.c | 56 ++++++++++++++++++++++++++++++++++ arch/arm/include/asm/arch-sunxi/dram.h | 4 +++ 2 files changed, 60 insertions(+)
diff --git a/arch/arm/cpu/armv7/sunxi/dram.c b/arch/arm/cpu/armv7/sunxi/dram.c index 4a72480..f87cbeb 100644 --- a/arch/arm/cpu/armv7/sunxi/dram.c +++ b/arch/arm/cpu/armv7/sunxi/dram.c @@ -445,6 +445,60 @@ static void mctl_ddr3_initialize(void) await_bits_clear(&dram->ccr, DRAM_CCR_INIT); }
+/* + * Perform impedance calibration on the DRAM controller side of the wire. + */ +static void mctl_set_impedance(u32 zq, u32 odt_en) +{ + struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE; + u32 reg_val; + u32 zprog = zq & 0xFF, zdata = (zq >> 8) & 0xFFFFF; + +#ifndef CONFIG_SUN7I + /* Appears that some kind of automatically initiated default + * ZQ calibration is already in progress at this point on sun4i/sun5i + * hardware, but not on sun7i. So it is reasonable to wait for its + * completion before doing anything else. */ + await_bits_set(&dram->zqsr, DRAM_ZQSR_ZDONE); +#endif + + /* ZQ calibration is not really useful unless ODT is enabled */ + if (!odt_en) + return; + +#ifdef CONFIG_SUN7I + /* Enabling ODT in SDR_IOCR on sun7i hardware results in a deadlock + * unless bit 24 is set in SDR_ZQCR1. Not much is known about the + * SDR_ZQCR1 register, but there are hints indicating that it might + * be related to periodic impedance re-calibration. This particular + * magic value is borrowed from the Allwinner boot0 bootloader, and + * using it helps to avoid troubles */ + writel((1 << 24) | (1 << 1), &dram->zqcr1); +#endif + + /* Needed at least for sun5i, because it does not self clear there */ + clrbits_le32(&dram->zqcr0, DRAM_ZQCR0_ZCAL); + + if (zdata) { + /* Set the user supplied impedance data */ + reg_val = DRAM_ZQCR0_ZDEN | zdata; + writel(reg_val, &dram->zqcr0); + /* no need to wait, this takes effect immediately */ + } else { + /* Do the calibration using the external resistor */ + reg_val = DRAM_ZQCR0_ZCAL | DRAM_ZQCR0_IMP_DIV(zprog); + writel(reg_val, &dram->zqcr0); + /* Wait for the new impedance configuration to settle */ + await_bits_set(&dram->zqsr, DRAM_ZQSR_ZDONE); + } + + /* Needed at least for sun5i, because it does not self clear there */ + clrbits_le32(&dram->zqcr0, DRAM_ZQCR0_ZCAL); + + /* Set I/O configure register */ + writel(DRAM_IOCR_ODT_EN(odt_en), &dram->iocr); +} + unsigned long dramc_init(struct dram_para *para) { struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE; @@ -505,6 +559,8 @@ unsigned long dramc_init(struct dram_para *para)
dramc_clock_output_en(1);
+ mctl_set_impedance(para->zq, para->odt_en); + mctl_set_cke_delay();
mctl_ddr3_reset(); diff --git a/arch/arm/include/asm/arch-sunxi/dram.h b/arch/arm/include/asm/arch-sunxi/dram.h index 67fbfad..4433eeb 100644 --- a/arch/arm/include/asm/arch-sunxi/dram.h +++ b/arch/arm/include/asm/arch-sunxi/dram.h @@ -159,6 +159,10 @@ struct dram_para {
#define DRAM_ZQCR0_IMP_DIV(n) (((n) & 0xff) << 20) #define DRAM_ZQCR0_IMP_DIV_MASK DRAM_ZQCR0_IMP_DIV(0xff) +#define DRAM_ZQCR0_ZCAL (1 << 31) /* Starts ZQ calibration when set to 1 */ +#define DRAM_ZQCR0_ZDEN (1 << 28) /* Uses ZDATA instead of doing calibration */ + +#define DRAM_ZQSR_ZDONE (1 << 31) /* ZQ calibration completion flag */
#define DRAM_IOCR_ODT_EN(n) ((((n) & 0x3) << 30) | ((n) & 0x3) << 0) #define DRAM_IOCR_ODT_EN_MASK DRAM_IOCR_ODT_EN(0x3)