Re: [PATCH v4] mmc: Make ID freq configurable

[Chris Ball <cjb@laptop.org>]

Hi Hein, thanks for resending this,

On Fri, Sep 03, 2010 at 05:34:53AM +0800, Hein_Tibosch wrote:
> In the latest releases of the mmc driver, the freq during initialization
> is set to a fixed 400 Khz. This was reportedly too fast for several
> users. As there doesn't seem to be an ideal frequency which-works-for-all,
> Pierre suggested to let the driver try several frequencies.
> 
> This patch implements that idea. It will try mmc-initialization using
> several frequencies from an array 400, 300, 200 and 100.
> I submitted it earlier but it's now adapted to and tested with kernel
> 2.6.36-rc3.
> 
> In case SDIO is broken, it'll still try to detect SDMEM, also at different
> freqs.
> 
> Signed-off-by: Hein Tibosch <hein_tibosch@yahoo.es>

Reviewed-and-Tested-by: Chris Ball <cjb@laptop.org>

I tested by modifying mmc_send_app_op_cond() to return timeouts for
various frequencies, and verified that the code correctly progresses
through the freqs[] table until reaching host->f_min, and can bring
up the card successfully on any of those retries.

In an earlier mail, you said:

> Here it tries 3 frequencies, which takes 290 ms:
> In a meanwhile it is doing other things, so not much time is wasted.

I decided to check this.  If my emulated failing of bringing up a card
at a given frequency is correct, 14ms per frequency attempt is spent in 
mdelay() rather than msleep().  I don't think this is a problem, though,
because you only take that hit if you have a card inserted that we're
unable to bring up at the default frequency -- the only alternative
would be to give up on the card.

If a host has no card inserted then we still try to detect a card on
all frequencies, but all of the paths in that case are msleep() rather
than mdelay(), so that's okay.

Two minor checkpatch fixes below:

> ---
> diff -Nurp a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> --- a/drivers/mmc/core/core.c	2010-08-29 23:36:04.000000000 +0800
> +++ b/drivers/mmc/core/core.c	2010-09-03 04:28:52.000000000 +0800
> @@ -907,12 +907,7 @@ static void mmc_power_up(struct mmc_host
>  	 */
>  	mmc_delay(10);
> 
> -	if (host->f_min > 400000) {
> -		pr_warning("%s: Minimum clock frequency too high for "
> -				"identification mode\n", mmc_hostname(host));
> -		host->ios.clock = host->f_min;
> -	} else
> -		host->ios.clock = 400000;
> +	host->ios.clock = host->f_init;
> 
>  	host->ios.power_mode = MMC_POWER_ON;
>  	mmc_set_ios(host);
> @@ -1404,6 +1399,8 @@ void mmc_rescan(struct work_struct *work
>  	u32 ocr;
>  	int err;
>  	unsigned long flags;
> +	int i;
> +	unsigned freqs[] = { 400000, 300000, 200000, 100000 };
> 
>  	spin_lock_irqsave(&host->lock, flags);
> 
> @@ -1443,55 +1440,64 @@ void mmc_rescan(struct work_struct *work
>  	if (host->ops->get_cd && host->ops->get_cd(host) == 0)
>  		goto out;
> 
> -	mmc_claim_host(host);
> +	for (i = 0; i < ARRAY_SIZE(freqs); i++) {
> +		mmc_claim_host(host);
> 
> -	mmc_power_up(host);
> -	sdio_reset(host);
> -	mmc_go_idle(host);
> +		if (freqs[i] >= host->f_min)
> +			host->f_init = freqs[i];
> +		else if (i && freqs[i-1] <= host->f_min)
> +			goto out;
> +		else
> +			host->f_init = host->f_min;
> 
> -	mmc_send_if_cond(host, host->ocr_avail);
> +		printk ("mmc_rescan: trying %u Hz\n", host->f_init);

Need a loglevel here, and an mmc_hostname.  Something like:

                pr_info("%s: %s: trying to init card at %u Hz\n",
                        mmc_hostname(host), __func__, host->f_init);

> +		mmc_power_up(host);
> +		sdio_reset(host);
> +		mmc_go_idle(host);
> 
> -	/*
> -	 * First we search for SDIO...
> -	 */
> -	err = mmc_send_io_op_cond(host, 0, &ocr);
> -	if (!err) {
> -		if (mmc_attach_sdio(host, ocr)) {
> -			mmc_claim_host(host);
> -			/* try SDMEM (but not MMC) even if SDIO is broken */
> -			if (mmc_send_app_op_cond(host, 0, &ocr))
> -				goto out_fail;
> +		mmc_send_if_cond(host, host->ocr_avail);
> +
> +		/*
> +		 * First we search for SDIO...
> +		 */
> +		err = mmc_send_io_op_cond(host, 0, &ocr);
> +		if (!err) {
> +			if (mmc_attach_sdio(host, ocr)) {
> +				mmc_claim_host(host);
> +				/* try SDMEM (but not MMC) even if SDIO is broken */

This breaks 80-chars, so:

                                /*
                                 * Try SDMEM (but not MMC) even if SDIO
                                 * is broken.
                                 */

> +				if (mmc_send_app_op_cond(host, 0, &ocr))
> +					goto out_fail;
> +
> +				if (mmc_attach_sd(host, ocr))
> +					mmc_power_off(host);
> +			}
> +			goto out;
> +		}
> 
> +		/*
> +		 * ...then normal SD...
> +		 */
> +		err = mmc_send_app_op_cond(host, 0, &ocr);
> +		if (!err) {
>  			if (mmc_attach_sd(host, ocr))
>  				mmc_power_off(host);
> +			goto out;
>  		}
> -		goto out;
> -	}
> 
> -	/*
> -	 * ...then normal SD...
> -	 */
> -	err = mmc_send_app_op_cond(host, 0, &ocr);
> -	if (!err) {
> -		if (mmc_attach_sd(host, ocr))
> -			mmc_power_off(host);
> -		goto out;
> -	}
> -
> -	/*
> -	 * ...and finally MMC.
> -	 */
> -	err = mmc_send_op_cond(host, 0, &ocr);
> -	if (!err) {
> -		if (mmc_attach_mmc(host, ocr))
> -			mmc_power_off(host);
> -		goto out;
> -	}
> +		/*
> +		 * ...and finally MMC.
> +		 */
> +		err = mmc_send_op_cond(host, 0, &ocr);
> +		if (!err) {
> +			if (mmc_attach_mmc(host, ocr))
> +				mmc_power_off(host);
> +			goto out;
> +		}
> 
>  out_fail:
> -	mmc_release_host(host);
> -	mmc_power_off(host);
> -
> +		mmc_release_host(host);
> +		mmc_power_off(host);
> +	}
>  out:
>  	if (host->caps & MMC_CAP_NEEDS_POLL)
>  		mmc_schedule_delayed_work(&host->detect, HZ);
> diff -Nurp a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> --- a/include/linux/mmc/host.h	2010-08-29 23:36:04.000000000 +0800
> +++ b/include/linux/mmc/host.h	2010-09-03 00:52:48.000000000 +0800
> @@ -123,6 +123,7 @@ struct mmc_host {
>  	const struct mmc_host_ops *ops;
>  	unsigned int		f_min;
>  	unsigned int		f_max;
> +	unsigned int		f_init;
>  	u32			ocr_avail;
>  	struct notifier_block	pm_notify;
> 
> ---

-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child