Re: [PATCH 05/11] mmc: core: Enable eMMC sleep commands to use HW busy polling

[Shawn Lin]

On 2021/5/5 0:12, Ulf Hansson wrote:
> After the eMMC sleep command (CMD5) has been sent, the card start signals
> busy on the DAT0 line, which can be monitored to understand when it's
> allowed to proceed to power off the VCC regulator.
>
> When MMC_CAP_WAIT_WHILE_BUSY isn't supported by the host the DAT0 line
> isn't being monitored for busy completion, but instead we are waiting a
> fixed period of time. The time corresponds to the sleep timeout that is
> specified in the EXT_CSD register of the eMMC card. This is many cases
> suboptimal, as the timeout corresponds to the worst case scenario.
>
> To improve the situation add support for HW busy polling through the
> ->card_busy() host ops, when the host supports this.

Reviewed-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>

> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> ---
>   drivers/mmc/core/mmc.c | 25 ++++++++++++++++++++-----
>   1 file changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 63a7bd0b239c..13074aa1f605 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1905,6 +1905,14 @@ static int mmc_can_sleep(struct mmc_card *card)
>   	return card->ext_csd.rev >= 3;
>   }
>   
> +static int mmc_sleep_busy_cb(void *cb_data, bool *busy)
> +{
> +	struct mmc_host *host = cb_data;
> +
> +	*busy = host->ops->card_busy(host);
> +	return 0;
> +}
> +
>   static int mmc_sleep(struct mmc_host *host)
>   {
>   	struct mmc_command cmd = {};
> @@ -1930,13 +1938,20 @@ static int mmc_sleep(struct mmc_host *host)
>   		goto out_release;
>   
>   	/*
> -	 * If the host does not wait while the card signals busy, then we will
> -	 * will have to wait the sleep/awake timeout.  Note, we cannot use the
> -	 * SEND_STATUS command to poll the status because that command (and most
> -	 * others) is invalid while the card sleeps.
> +	 * If the host does not wait while the card signals busy, then we can
> +	 * try to poll, but only if the host supports HW polling, as the
> +	 * SEND_STATUS cmd is not allowed. If we can't poll, then we simply need
> +	 * to wait the sleep/awake timeout.
>   	 */
> -	if (!use_r1b_resp || !(host->caps & MMC_CAP_WAIT_WHILE_BUSY))
> +	if (host->caps & MMC_CAP_WAIT_WHILE_BUSY && use_r1b_resp)
> +		goto out_release;
> +
> +	if (!host->ops->card_busy) {
>   		mmc_delay(timeout_ms);
> +		goto out_release;
> +	}
> +
> +	err = __mmc_poll_for_busy(card, timeout_ms, &mmc_sleep_busy_cb, host);
>   
>   out_release:
>   	mmc_retune_release(host);