linux-kernel - Re: [PATCH v6 17/17] mmc: sdhci-cadence: Support mmc hardware reset

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Date:   Mon, 22 Aug 2022 12:53:22 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Brad Larson <brad@...sando.io>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, adrian.hunter@...el.com,
        alcooperx@...il.com, andy.shevchenko@...il.com, arnd@...db.de,
        blarson@....com, brijeshkumar.singh@....com,
        catalin.marinas@....com, gsomlo@...il.com, gerg@...ux-m68k.org,
        krzk@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        lee.jones@...aro.org, broonie@...nel.org,
        yamada.masahiro@...ionext.com, p.zabel@...gutronix.de,
        piotrs@...ence.com, p.yadav@...com, rdunlap@...radead.org,
        robh+dt@...nel.org, samuel@...lland.org, fancer.lancer@...il.com,
        suravee.suthikulpanit@....com, thomas.lendacky@....com,
        will@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v6 17/17] mmc: sdhci-cadence: Support mmc hardware reset

On Sat, 20 Aug 2022 at 21:58, Brad Larson <brad@...sando.io> wrote:
>
> From: Brad Larson <blarson@....com>
>
> Add support for mmc hardware reset with a reset-controller
> which would need to be enabled in the device tree with
> a supporting driver.  The default is disabled for all
> existing designs.
>
> Signed-off-by: Brad Larson <blarson@....com>
> ---
>  drivers/mmc/host/sdhci-cadence.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
> index c662c63d49fa..35d37b9aba63 100644
> --- a/drivers/mmc/host/sdhci-cadence.c
> +++ b/drivers/mmc/host/sdhci-cadence.c
> @@ -12,6 +12,7 @@
>  #include <linux/mmc/mmc.h>
>  #include <linux/of.h>
>  #include <linux/of_device.h>
> +#include <linux/reset.h>
>
>  #include "sdhci-pltfm.h"
>
> @@ -70,6 +71,7 @@ struct sdhci_cdns_priv {
>         spinlock_t wrlock;      /* write lock */
>         bool enhanced_strobe;
>         void (*priv_writel)(struct sdhci_cdns_priv *priv, u32 val, void __iomem *reg);
> +       struct reset_control *rst_hw;
>         unsigned int nr_phy_params;
>         struct sdhci_cdns_phy_param phy_params[];
>  };
> @@ -458,6 +460,22 @@ static void sdhci_cdns_hs400_enhanced_strobe(struct mmc_host *mmc,
>                                          SDHCI_CDNS_HRS06_MODE_MMC_HS400);
>  }
>
> +static void sdhci_mmc_hw_reset(struct mmc_host *mmc)

Nitpick: Probably better to be consistent with the prefixes for
function names. So, I suggest changing this to
"sdhci_cdns_mmc_hw_reset".

> +{
> +       struct sdhci_host *host = mmc_priv(mmc);
> +       struct sdhci_cdns_priv *priv = sdhci_cdns_priv(host);
> +
> +       dev_info(mmc_dev(host->mmc), "emmc hardware reset\n");

Maybe it's sufficient with dev_dbg?

> +
> +       reset_control_assert(priv->rst_hw);
> +       /* For eMMC, minimum is 1us but give it 9us for good measure */
> +       udelay(9);
> +
> +       reset_control_deassert(priv->rst_hw);
> +       /* For eMMC, minimum is 200us but give it 300us for good measure */
> +       usleep_range(300, 1000);
> +}
> +
>  static int sdhci_cdns_probe(struct platform_device *pdev)
>  {
>         struct sdhci_host *host;
> @@ -520,6 +538,17 @@ static int sdhci_cdns_probe(struct platform_device *pdev)
>         if (ret)
>                 goto free;
>
> +       if (host->mmc->caps & MMC_CAP_HW_RESET) {
> +               priv->rst_hw = devm_reset_control_get_optional_exclusive(dev, "hw");
> +               if (IS_ERR(priv->rst_hw)) {
> +                       ret = PTR_ERR(priv->rst_hw);
> +                       if (ret == -ENOENT)
> +                               priv->rst_hw = NULL;
> +               } else {
> +                       host->mmc_host_ops.card_hw_reset = sdhci_mmc_hw_reset;
> +               }
> +       }
> +
>         ret = sdhci_add_host(host);
>         if (ret)
>                 goto free;
> --

Other than the comments above, I wonder about what merging strategy we
should use for the series. I believe it looks fine for me to pick up
the mmc related patches, thus we can apply patches on a per subsystem
basis, right?

Kind regards
Uffe