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SubjectRe: [PATCH v2 1/6] mmc: sunxi: Always set signal delay to 0 for A64
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On 09/01/17 16:46, Maxime Ripard wrote:
> 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.
>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
> 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 b1d1303389a7..ea9552a0d820 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;
> }
> @@ -806,7 +784,13 @@ 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 and older SoCs).

Which older SoCs have this calibration register and a DS signal?
Is that supposed to mean "other" SoCs?

Other than that:

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre.

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