From 860fdf89b92e740b19d1160406df98e5302a9300 Mon Sep 17 00:00:00 2001 From: Maxime Ripard Date: Fri, 27 Jan 2017 22:38:35 +0100 Subject: [PATCH] mmc: sunxi: Always set signal delay to 0 for A64 Experience have shown that the using the autocalibration could severely degrade the performances of the MMC bus. Allwinner is using in its BSP a delay set to 0 for all the modes but HS400. Remove the calibration code for now, and add comments to document our findings. Reviewed-by: Andre Przywara Signed-off-by: Maxime Ripard Tested-by: Florian Vaussard Acked-by: Chen-Yu Tsai Signed-off-by: Ulf Hansson --- drivers/mmc/host/sunxi-mmc.c | 50 ++++++++++++------------------------ 1 file changed, 17 insertions(+), 33 deletions(-) diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c index 019f95e8e7c5..b9c8a62bc212 100644 --- a/drivers/mmc/host/sunxi-mmc.c +++ b/drivers/mmc/host/sunxi-mmc.c @@ -683,41 +683,19 @@ static int sunxi_mmc_oclk_onoff(struct sunxi_mmc_host *host, u32 oclk_en) static int sunxi_mmc_calibrate(struct sunxi_mmc_host *host, int reg_off) { - u32 reg = readl(host->reg_base + reg_off); - u32 delay; - unsigned long timeout; - if (!host->cfg->can_calibrate) return 0; - reg &= ~(SDXC_CAL_DL_MASK << SDXC_CAL_DL_SW_SHIFT); - reg &= ~SDXC_CAL_DL_SW_EN; - - writel(reg | SDXC_CAL_START, host->reg_base + reg_off); - - dev_dbg(mmc_dev(host->mmc), "calibration started\n"); - - timeout = jiffies + HZ * SDXC_CAL_TIMEOUT; - - while (!((reg = readl(host->reg_base + reg_off)) & SDXC_CAL_DONE)) { - if (time_before(jiffies, timeout)) - cpu_relax(); - else { - reg &= ~SDXC_CAL_START; - writel(reg, host->reg_base + reg_off); - - return -ETIMEDOUT; - } - } - - delay = (reg >> SDXC_CAL_DL_SHIFT) & SDXC_CAL_DL_MASK; - - reg &= ~SDXC_CAL_START; - reg |= (delay << SDXC_CAL_DL_SW_SHIFT) | SDXC_CAL_DL_SW_EN; - - writel(reg, host->reg_base + reg_off); - - dev_dbg(mmc_dev(host->mmc), "calibration ended, reg is 0x%x\n", reg); + /* + * FIXME: + * This is not clear how the calibration is supposed to work + * yet. The best rate have been obtained by simply setting the + * delay to 0, as Allwinner does in its BSP. + * + * The only mode that doesn't have such a delay is HS400, that + * is in itself a TODO. + */ + writel(SDXC_CAL_DL_SW_EN, host->reg_base + reg_off); return 0; } @@ -809,7 +787,13 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host, if (ret) return ret; - /* TODO: enable calibrate on sdc2 SDXC_REG_DS_DL_REG of A64 */ + /* + * FIXME: + * + * In HS400 we'll also need to calibrate the data strobe + * signal. This should only happen on the MMC2 controller (at + * least on the A64). + */ return sunxi_mmc_oclk_onoff(host, 1); }