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SubjectRe: [PATCH] mmc: sdhci-cadence: send tune request twice to work around errata
On 27 March 2018 at 11:29, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> Cadence sent out an errata report to their customers of this IP.
> This errata is not so severe, but the tune request should be sent
> twice to avoid the potential issue.
>
> Quote from the report:
>
> Problem Summary
> ---------------
> The IP6116 SD/eMMC PHY design has a timing issue on receive data path.
> This issue may lead to an incorrect values of read/write pointers of
> the synchronization FIFO. Such a situation can happen at the SDR104
> and HS200 tuning procedure when the PHY is requested to change a phase
> of sampling clock when moving to the next tuning iteration.
>
> Workarounds
> -----------
> The following are valid workarounds to resolve the issue:
>
> 1. In eMMC mode, software sends tune request twice instead of once at
> each iteration. This means that the clock phase is not changed on
> the second request so there is no potential for clock instability.
> 2. In SD mode, software must not use the hardware tuning and instead
> perform an almost identical procedure to eMMC, using the HRS34 Tune
> Force register.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Do you want this to be tagged for stable as well? And perhaps you
could add a fixes tag?

Kind regards
Uffe

> ---
>
> drivers/mmc/host/sdhci-cadence.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
> index 0f589e2..bc30d16 100644
> --- a/drivers/mmc/host/sdhci-cadence.c
> +++ b/drivers/mmc/host/sdhci-cadence.c
> @@ -253,6 +253,7 @@ static int sdhci_cdns_set_tune_val(struct sdhci_host *host, unsigned int val)
> struct sdhci_cdns_priv *priv = sdhci_cdns_priv(host);
> void __iomem *reg = priv->hrs_addr + SDHCI_CDNS_HRS06;
> u32 tmp;
> + int i, ret;
>
> if (WARN_ON(!FIELD_FIT(SDHCI_CDNS_HRS06_TUNE, val)))
> return -EINVAL;
> @@ -260,11 +261,24 @@ static int sdhci_cdns_set_tune_val(struct sdhci_host *host, unsigned int val)
> tmp = readl(reg);
> tmp &= ~SDHCI_CDNS_HRS06_TUNE;
> tmp |= FIELD_PREP(SDHCI_CDNS_HRS06_TUNE, val);
> - tmp |= SDHCI_CDNS_HRS06_TUNE_UP;
> - writel(tmp, reg);
>
> - return readl_poll_timeout(reg, tmp, !(tmp & SDHCI_CDNS_HRS06_TUNE_UP),
> - 0, 1);
> + /*
> + * Workaround for IP errata:
> + * The IP6116 SD/eMMC PHY design has a timing issue on receive data
> + * path. Send tune request twice.
> + */
> + for (i = 0; i < 2; i++) {
> + tmp |= SDHCI_CDNS_HRS06_TUNE_UP;
> + writel(tmp, reg);
> +
> + ret = readl_poll_timeout(reg, tmp,
> + !(tmp & SDHCI_CDNS_HRS06_TUNE_UP),
> + 0, 1);
> +
> + return ret;
> + }
> +
> + return 0;
> }
>
> static int sdhci_cdns_execute_tuning(struct mmc_host *mmc, u32 opcode)
> --
> 2.7.4
>

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