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Subject: Re: [PATCH RFC] mmc: sdhci-msm: Toggle fifo write clk after ungating sdcc clk
From:   Stephen Boyd <sboyd@kernel.org>
Cc:     linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
        agross@kernel.org, linux-mmc-owner@vger.kernel.org,
        Sayali Lokhande <sayalil@codeaurora.org>
To:     Sayali Lokhande <sayalil@codeaurora.org>, adrian.hunter@intel.com,
        asutoshd@codeaurora.org, bjorn.andersson@linaro.org,
        georgi.djakov@linaro.org, mka@chromium.org, ppvk@codeaurora.org,
        rampraka@codeaurora.org, robh+dt@kernel.org,
        stummala@codeaurora.org, ulf.hansson@linaro.org,
        vbadigan@codeaurora.org
Date:   Thu, 20 Feb 2020 10:02:50 -0800
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Quoting Sayali Lokhande (2020-02-20 01:20:46)
> From: Ram Prakash Gupta <rampraka@codeaurora.org>
>=20
> During GCC level clock gating of MCLK, the async FIFO

Is this automatic hardware clock gating?

> gets into some hang condition, such that for the next
> transfer after MCLK ungating, first bit of CMD response
> doesn't get written in to the FIFO. This cause the CPSM
> to hang eventually leading to SW timeout.
>=20
> To fix the issue, toggle the FIFO write clock after
> MCLK ungated to get the FIFO pointers and flags to
> valid states.
>=20
> Change-Id: Ibef2d1d283ac0b6983c609a4abc98bc574d31fa6
> Signed-off-by: Ram Prakash Gupta <rampraka@codeaurora.org>
> Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>
> ---
>  drivers/mmc/host/sdhci-msm.c | 43 ++++++++++++++++++++++++++++++++++++++=
+++++
>  1 file changed, 43 insertions(+)
>=20
> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> index c3a160c..eaa3e95 100644
> --- a/drivers/mmc/host/sdhci-msm.c
> +++ b/drivers/mmc/host/sdhci-msm.c
> @@ -1554,6 +1556,43 @@ static void __sdhci_msm_set_clock(struct sdhci_hos=
t *host, unsigned int clock)
>         sdhci_enable_clk(host, clk);
>  }
> =20
> +/*
> + * After MCLK ugating, toggle the FIFO write clock to get

What is ugating?

> + * the FIFO pointers and flags to valid state.
> + */
> +static void sdhci_msm_toggle_fifo_write_clk(struct sdhci_host *host)
> +{
> +       struct sdhci_pltfm_host *pltfm_host =3D sdhci_priv(host);
> +       struct sdhci_msm_host *msm_host =3D sdhci_pltfm_priv(pltfm_host);
> +       const struct sdhci_msm_offset *msm_offset =3D
> +                                       msm_host->offset;
> +       struct mmc_card *card =3D host->mmc->card;
> +
> +       if (msm_host->tuning_done ||
> +                       (card && card->ext_csd.strobe_support &&
> +                       card->host->ios.enhanced_strobe)) {
> +               /*
> +                * set HC_REG_DLL_CONFIG_3[1] to select MCLK as
> +                * DLL input clock
> +                */