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

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Date:   Mon, 22 Aug 2022 09:03:22 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Brad Larson <brad@...sando.io>,
        linux-arm-kernel@...ts.infradead.org
Cc:     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,
        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,
        ulf.hansson@...aro.org, will@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v6 17/17] mmc: sdhci-cadence: Support mmc hardware reset

Hi Brad,

On Sa, 2022-08-20 at 12:57 -0700, Brad Larson wrote:
[...]
> +static void sdhci_mmc_hw_reset(struct mmc_host *mmc)
> +{
> +	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");
> +
> +	reset_control_assert(priv->rst_hw);
> +	/* For eMMC, minimum is 1us but give it 9us for good measure */
> +	udelay(9);

At a glance, this seems excessive. Is there a reason 9 us is better
than, say, 2 or 3?

[...]
> @@ -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");

This should be described in cdns,sdhci.yaml first.

regards
Philipp