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    SubjectRe: [PATCH 13/40] mmc: tegra: Poll for calibration completion
    On Thu, Aug 09, 2018 at 03:56:38PM +0300, Aapo Vienamo wrote:
    > On Thu, 9 Aug 2018 14:46:16 +0200
    > Thierry Reding <thierry.reding@gmail.com> wrote:
    >
    > > On Wed, Aug 01, 2018 at 07:32:03PM +0300, Aapo Vienamo wrote:
    > > > Implement polling with 10 ms timeout for automatic pad drive strength
    > > > calibration.
    > > >
    > > > Signed-off-by: Aapo Vienamo <avienamo@nvidia.com>
    > > > ---
    > > > drivers/mmc/host/sdhci-tegra.c | 21 ++++++++++++++++-----
    > > > 1 file changed, 16 insertions(+), 5 deletions(-)
    > > >
    > > > diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
    > > > index 7d98455..c8ff267 100644
    > > > --- a/drivers/mmc/host/sdhci-tegra.c
    > > > +++ b/drivers/mmc/host/sdhci-tegra.c
    > > > @@ -16,6 +16,7 @@
    > > > #include <linux/err.h>
    > > > #include <linux/module.h>
    > > > #include <linux/init.h>
    > > > +#include <linux/iopoll.h>
    > > > #include <linux/platform_device.h>
    > > > #include <linux/clk.h>
    > > > #include <linux/io.h>
    > > > @@ -50,6 +51,9 @@
    > > > #define SDHCI_AUTO_CAL_START BIT(31)
    > > > #define SDHCI_AUTO_CAL_ENABLE BIT(29)
    > > >
    > > > +#define SDHCI_TEGRA_AUTO_CAL_STATUS 0x1ec
    > > > +#define SDHCI_TEGRA_AUTO_CAL_ACTIVE BIT(31)
    > > > +
    > > > #define NVQUIRK_FORCE_SDHCI_SPEC_200 BIT(0)
    > > > #define NVQUIRK_ENABLE_BLOCK_GAP_DET BIT(1)
    > > > #define NVQUIRK_ENABLE_SDHCI_SPEC_300 BIT(2)
    > > > @@ -228,13 +232,20 @@ static void tegra_sdhci_reset(struct sdhci_host *host, u8 mask)
    > > >
    > > > static void tegra_sdhci_pad_autocalib(struct sdhci_host *host)
    > > > {
    > > > - u32 val;
    > > > + u32 reg;
    > > > + int ret;
    > > > +
    > > > + reg = sdhci_readl(host, SDHCI_TEGRA_AUTO_CAL_CONFIG);
    > > > + reg |= SDHCI_AUTO_CAL_ENABLE | SDHCI_AUTO_CAL_START;
    > > > + sdhci_writel(host, reg, SDHCI_TEGRA_AUTO_CAL_CONFIG);
    > > >
    > >
    > > I know this is preexisting, but I want to make sure we cover this so we
    > > don't run into this down the road: do these bits automatically clear on
    > > calibration completion? Can we run these multiple times and get
    > > everything properly calibrated?
    >
    > The TRM states in the pad auto-calibration procedure description that
    > this bit should not be cleared.

    It says that SDHCI_AUTO_CAL_ENABLE shouldn't be cleared after
    calibration completes, but I'm wondering how recalibration is going to
    happen on a second run.

    I guess if we never turn off calibration, then it will continue to run
    forever, but does that also work if we go back to a mode that doesn't
    require calibration?

    So perhaps what we need is to clear SDHCI_AUTO_CAL_ENABLE when going to
    such a mode. And perhaps we need to clear SDHCI_AUTO_CAL_START after the
    calibration is complete.

    Anyway, lots of unanswered questions and if the above works, I'm fine
    with merging it as-is. If we find out that something else is needed at a
    later point we can always fix it up later.

    Thierry
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