linux-kernel - Re: [PATCH] mmc: append a file to change host clock at run time

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Message-ID: <4CB568C0.9030906@nokia.com>
Date:	Wed, 13 Oct 2010 11:07:28 +0300
From:	Adrian Hunter <adrian.hunter@...ia.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Ball <cjb@...top.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Shevchenko Andriy (EXT-Teleca/Helsinki)" 
	<ext-andriy.shevchenko@...ia.com>
Subject: Re: [PATCH] mmc: append a file to change host clock at run time

On 12/10/10 18:17, Andy Shevchenko wrote:
> For debugging power managment features there is quite convenient to have a
> possibility to change MMC host controller clock at run time. This patch adds
> 'clock' file under MMC host root of debugfs.
>
> Usage as follows:
>
> 	# cat /sys/kernel/debug/mmc0/clock
> 	24000000
>
> 	# echo "1000000000">  /sys/kernel/debug/mmc0/clock
> 	# cat /sys/kernel/debug/mmc0/clock
> 	52000000
>
> 	# echo "48000000">  /sys/kernel/debug/mmc0/clock
> 	# cat /sys/kernel/debug/mmc0/clock
> 	48000000
>
> The second piece of example shows limits which are applied accordingly to used
> host driver.
>
> Signed-off-by: Andy Shevchenko<ext-andriy.shevchenko@...ia.com>
> ---
>   drivers/mmc/core/debugfs.c |   33 +++++++++++++++++++++++++++++++--
>   1 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/debugfs.c b/drivers/mmc/core/debugfs.c
> index 96d10f4..4ff109f 100644
> --- a/drivers/mmc/core/debugfs.c
> +++ b/drivers/mmc/core/debugfs.c
> @@ -133,6 +133,31 @@ static const struct file_operations mmc_ios_fops = {
>   	.release	= single_release,
>   };
>
> +static int mmc_clock_opt_get(void *data, u64 *val)
> +{
> +	struct mmc_host *host = data;
> +
> +	*val = host->ios.clock;
> +
> +	return 0;
> +}
> +
> +static int mmc_clock_opt_set(void *data, u64 val)
> +{
> +	struct mmc_host *host = data;
> +
> +	/* We need this check due to input value is u64 */
> +	if (val>  host->f_max)
> +		return -EINVAL;
> +
> +	mmc_set_clock(host, (unsigned int) val);

Probably need to claim the host here otherwise you might
be changing the clock while a request is in progress

> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(mmc_clock_fops, mmc_clock_opt_get, mmc_clock_opt_set,
> +	"%llu\n");
> +
>   void mmc_add_host_debugfs(struct mmc_host *host)
>   {
>   	struct dentry *root;
> @@ -149,11 +174,15 @@ void mmc_add_host_debugfs(struct mmc_host *host)
>   	host->debugfs_root = root;
>
>   	if (!debugfs_create_file("ios", S_IRUSR, root, host,&mmc_ios_fops))
> -		goto err_ios;
> +		goto err_node;
> +
> +	if (!debugfs_create_file("clock", S_IRUSR | S_IWUSR, root, host,
> +			&mmc_clock_fops))
> +		goto err_node;
>
>   	return;
>
> -err_ios:
> +err_node:
>   	debugfs_remove_recursive(root);
>   	host->debugfs_root = NULL;
>   err_root:

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