linux-kernel - Re: [PATCH] mmc: change mmc_delay() to use usleep

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Message-ID: <alpine.DEB.2.00.1201132308530.24003@kernel.research.nokia.com>
Date:	Fri, 13 Jan 2012 23:38:26 +0200 (EET)
From:	Aaro Koskinen <aaro.koskinen@...ia.com>
To:	Dmitry Antipov <dmitry.antipov@...aro.org>
cc:	Chris Ball <cjb@...top.org>, patches@...aro.org,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: change mmc_delay() to use usleep_range()

Hi,

On Fri, 13 Jan 2012, Dmitry Antipov wrote:
> Use the usleep_range() to simplify mmc_delay() and give some more
> accuracy to it - but with an exception of mmc_card_sleepawake():
> since sleep/awake timeout varies in a wide range, different
> delay methods should be used.
>
> Signed-off-by: Dmitry Antipov <dmitry.antipov@...aro.org>

[...]

> +	if (!(host->caps & MMC_CAP_WAIT_WHILE_BUSY)) {
> +		/* JEDEC MMCA 4.41 specifies the timeout value is in 200ns..838.86ms
> +		   range. Round it up to 1us and use an appropriate delay method. */
> +		unsigned long us = DIV_ROUND_UP(card->ext_csd.sa_timeout, 10);
> +		if (us < 10)
> +			udelay(us);
> +		else
> +			usleep_range(us, us + 100);
> +	}

I think this part of the patch is over-engineered. What difference
does it make in practice if you round it up to a bigger value so that
usleep_range() makes always sense? The S/A timeout defines the max time
the transition can take, it's not wrong to wait a bit longer. Also note
that udelay() is not accurate so you need to add some margin anyway.

A.
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