linux-kernel - Re: [PATCH v3 5/5] mmc: sdhci-of-aspeed: Assert/Deassert reset signal before probing eMMC

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Message-ID: <20210506102458.GA20777@pengutronix.de>
Date:   Thu, 6 May 2021 12:24:58 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Steven Lee <steven_lee@...eedtech.com>
Cc:     Andrew Jeffery <andrew@...id.au>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Joel Stanley <joel@....id.au>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ryan Chen <ryanchen.aspeed@...il.com>,
        "moderated list:ASPEED SD/MMC DRIVER" <linux-aspeed@...ts.ozlabs.org>,
        "moderated list:ASPEED SD/MMC DRIVER" <openbmc@...ts.ozlabs.org>,
        "open list:ASPEED SD/MMC DRIVER" <linux-mmc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>, Hongweiz@....com,
        ryan_chen@...eedtech.com, chin-ting_kuo@...eedtech.com
Subject: Re: [PATCH v3 5/5] mmc: sdhci-of-aspeed: Assert/Deassert reset
 signal before probing eMMC

Hi Steven,

On Thu, May 06, 2021 at 06:03:12PM +0800, Steven Lee wrote:
> For cleaning up the AST2600 eMMC controller, the reset signal should be
> asserted and deasserted before it is probed.
> 
> Signed-off-by: Steven Lee <steven_lee@...eedtech.com>
> ---
>  drivers/mmc/host/sdhci-of-aspeed.c | 49 ++++++++++++++++++++++++------
>  1 file changed, 40 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-of-aspeed.c b/drivers/mmc/host/sdhci-of-aspeed.c
> index 4979f98ffb52..8ef06f32abff 100644
> --- a/drivers/mmc/host/sdhci-of-aspeed.c
> +++ b/drivers/mmc/host/sdhci-of-aspeed.c
[...]
> @@ -533,11 +545,22 @@ static struct platform_driver aspeed_sdhci_driver = {
>  	.remove		= aspeed_sdhci_remove,
>  };
>  
> +static const struct of_device_id aspeed_sdc_of_match[] = {
> +	{ .compatible = "aspeed,ast2400-sd-controller", },
> +	{ .compatible = "aspeed,ast2500-sd-controller", },
> +	{ .compatible = "aspeed,ast2600-sd-controller", .data = &ast2600_sdc_info},
> +	{ }
> +};
> +
> +MODULE_DEVICE_TABLE(of, aspeed_sdc_of_match);
> +
>  static int aspeed_sdc_probe(struct platform_device *pdev)
>  
>  {
>  	struct device_node *parent, *child;
>  	struct aspeed_sdc *sdc;
> +	const struct of_device_id *match = NULL;
> +	const struct aspeed_sdc_info *info = NULL;

There is no need to initialize these variables to NULL, see below:

>  	int ret;
>  
>  	sdc = devm_kzalloc(&pdev->dev, sizeof(*sdc), GFP_KERNEL);
> @@ -546,6 +569,23 @@ static int aspeed_sdc_probe(struct platform_device *pdev)
>  
>  	spin_lock_init(&sdc->lock);
>  
> +	match = of_match_device(aspeed_sdc_of_match, &pdev->dev);

match is set unconditionally before it is used,

> +	if (!match)
> +		return -ENODEV;
> +
> +	if (match->data)
> +		info = match->data;

and info could be set unconditionally as well:

	info = match->data;

> +	if (info) {
> +		if (info->flag & PROBE_AFTER_ASSET_DEASSERT) {
> +			sdc->rst = devm_reset_control_get(&pdev->dev, NULL);

Please use devm_reset_control_get_exclusive() or
devm_reset_control_get_optional_exclusive().

> +			if (!IS_ERR(sdc->rst)) {

Please just return errors here instead of ignoring them.
The reset_control_get_optional variants return NULL in case the
device node doesn't contain a resets phandle, in case you really
consider this reset to be optional even though the flag is set?

> +				reset_control_assert(sdc->rst);
> +				reset_control_deassert(sdc->rst);

Is there no need for delays between assertion and deassertion or after
the reset is deasserted?

> +			}
> +		}
> +	}
> +
>  	sdc->clk = devm_clk_get(&pdev->dev, NULL);
>  	if (IS_ERR(sdc->clk))
>  		return PTR_ERR(sdc->clk);

In general, I would assert/deassert the reset only after all resources
are successfully acquired. This might avoid unnecessary resets in case
of probe deferrals.

regards
Philipp