[PATCH 5/6] mmc: sdhci: calculate max_discard_to dynamically for SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK

[Shawn Guo]

On Tue, Dec 10, 2013 at 08:56:07PM +0800, Dong Aisheng wrote:
> For host controllers using SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK, since the card
> clock is changed dynamically for different cards, it does not make sense
> to use the maximum host clock to calculate max_discard_to which may lead
> the max_discard_to to be much smaller than its capbility and affect the card
> discard performance a lot.
> e.g. the host clock is 200Mhz, but the card is working on 50Mhz. Then the
> max_discard_to is only 1/4 of its real capbility.
> 
> In this patch, it uses the actual_clock to calculate the max_discard_to
> dynamically as long as a new clock speed is set.
> 
> Tested with a high speed SDHC card shows:
> Originally:
> mmc1: new high speed SDHC card at address aaaa
> mmc1: calculated max. discard sectors 49152 for timeout 1355 ms
> Now:
> mmc1: new high speed SDHC card at address aaaa
> mmc1: calculated max. discard sectors 712704 for timeout 5422 ms
> The max_discard_sectors will increase a lot which will also improve discard
> performance a lot.
> 
> The one known limitation of this approach is that it does not cover the special
> case for user changes the clock via sysfs, since the max_discard_to is only
> initialised for one time during the mmc queue init.
> 
> Signed-off-by: Dong Aisheng <b29396 at freescale.com>
> ---
>  drivers/mmc/host/sdhci.c |   27 +++++++++++++++++++++------
>  1 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 4cc3bd6..9be8a79 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1143,14 +1143,14 @@ static void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
>  	unsigned long timeout;
>  
>  	if (clock && clock == host->clock)
> -		return;
> +		goto out;

I do not quite understand this change.  Why do we need to recalculate
max_discard_to if the clock does not change since the last time that
the function is called?

Shawn

>  
>  	host->mmc->actual_clock = 0;
>  
>  	if (host->ops->set_clock) {
>  		host->ops->set_clock(host, clock);
>  		if (host->quirks & SDHCI_QUIRK_NONSTANDARD_CLOCK)
> -			return;
> +			goto out;
>  	}
>  
>  	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
> @@ -1249,6 +1249,19 @@ clock_set:
>  
>  out:
>  	host->clock = clock;
> +
> +	/* update timeout_clk and max_discard_to once the SDCLK is changed */
> +	if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK && clock) {
> +		host->timeout_clk = host->mmc->actual_clock ?
> +					host->mmc->actual_clock / 1000 :
> +					host->clock / 1000;
> +		if (host->ops->get_max_timeout)
> +			host->mmc->max_discard_to =
> +					host->ops->get_max_timeout(host);
> +		else
> +			host->mmc->max_discard_to = (1 << 27) /
> +					host->timeout_clk;
> +	}
>  }
>  
>  static inline void sdhci_update_clock(struct sdhci_host *host)
> @@ -2939,10 +2952,12 @@ int sdhci_add_host(struct sdhci_host *host)
>  	if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK)
>  		host->timeout_clk = mmc->f_max / 1000;
>  
> -	if (host->ops->get_max_timeout)
> -		mmc->max_discard_to = host->ops->get_max_timeout(host);
> -	else
> -		mmc->max_discard_to = (1 << 27) / host->timeout_clk;
> +	if (!(host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK)) {
> +		if (host->ops->get_max_timeout)
> +			mmc->max_discard_to = host->ops->get_max_timeout(host);
> +		else
> +			mmc->max_discard_to = (1 << 27) / host->timeout_clk;
> +	}
>  
>  	mmc->caps |= MMC_CAP_SDIO_IRQ | MMC_CAP_ERASE | MMC_CAP_CMD23;
>  
> -- 
> 1.7.2.rc3
> 
>