linux-kernel - Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow

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Date:   Mon, 28 Feb 2022 17:12:55 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Ricky WU <ricky_wu@...ltek.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "kai.heng.feng@...onical.com" <kai.heng.feng@...onical.com>,
        "tommyhebb@...il.com" <tommyhebb@...il.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow

On Tue, 22 Feb 2022 at 08:28, Ricky WU <ricky_wu@...ltek.com> wrote:
>
> After 1ms stabilizing the voltage time
> add "Host provides at least 74 Clocks
> before issuing first command" that is
> spec definition
>
> Signed-off-by: Ricky Wu <ricky_wu@...ltek.com>
> ---
>  drivers/mmc/host/rtsx_pci_sdmmc.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/mmc/host/rtsx_pci_sdmmc.c b/drivers/mmc/host/rtsx_pci_sdmmc.c
> index 2a3f14afe9f8..e016d720e453 100644
> --- a/drivers/mmc/host/rtsx_pci_sdmmc.c
> +++ b/drivers/mmc/host/rtsx_pci_sdmmc.c
> @@ -940,10 +940,17 @@ static int sd_power_on(struct realtek_pci_sdmmc *host)
>         if (err < 0)
>                 return err;
>
> +       mdelay(1);
> +
>         err = rtsx_pci_write_register(pcr, CARD_OE, SD_OUTPUT_EN, SD_OUTPUT_EN);
>         if (err < 0)
>                 return err;
>
> +       /* send init 74 clocks */
> +       rtsx_pci_write_register(pcr, SD_BUS_STAT, SD_CLK_TOGGLE_EN, SD_CLK_TOGGLE_EN);
> +       mdelay(5);
> +       rtsx_pci_write_register(pcr, SD_BUS_STAT, SD_CLK_TOGGLE_EN, 0);
> +
>         if (PCI_PID(pcr) == PID_5261) {
>                 /*
>                  * If test mode is set switch to SD Express mandatorily,

As you probably are aware of, the mmc core uses three power states
(MMC_POWER_ON, MMC_POWER_UP and MMC_POWER_OFF) to manage the
initialization, while it invokes the ->set_ios() callback for the mmc
host driver. During these steps the core also tries to manage the
different delays that are needed according to the eMMC/SD specs. You
may have a look at mmc_power_up() in drivers/mmc/core/core.c. In the
rtsx case, MMC_POWER_ON and MMC_POWER_UP are treated as one single
step.

Moreover, it has turned out that some mmc HWs are actually controlling
these delays during the initialization themselves, which makes the
delays in the core superfluous. Therefore we have made the delays
configurable for host drivers. For DT based platforms, we have the DT
property "post-power-on-delay-ms" and for others, it's perfectly fine
to update host->power_delay_ms before calling mmc_add_host().

Would it be possible to take advantage of the above "features" from
the core, to avoid hard coded and superfluous delays?

Kind regards
Uffe