Re: [PATCH v7 1/2] mmc: core: enhance card removal judgement for slow removal

[Philip Rakity <prakity@nvidia.com>]

Reviewed-by: Philip Rakity <prakity@nvidia.com>

On Feb 28, 2013, at 7:29 AM, Kevin Liu <kliu5@marvell.com> wrote:

> Function _mmc_detect_card_removed will be called to know whether
> the card is still present when host->bus_ops->detect is called.
> In current code, the return value of this function generally only
> depend on the result of sending cmd13 to card, which may not safe
> for card with detection support like slot gpio detection.
> Because the communication status between host and card may out of
> sync with the detect status if remove the card slowly or hands shake
> during the process. The direct reason is the async between card
> detect switch and card/slot pad contaction in hardware, which is
> defined by spec.
> 
> The spec define card insert/remove sequence as below (both standard size
> SD card and MicroSD card have the same sequence):
> "Part 1 Standard Size SD Card Mechanical Addendum Ver4.00 Final,
> Appendix C: Card Detection Switch" (Take normally open type as example)
> a)SD card insertion sequence:
>  The card detection switch should be turned on after all SD card
>  contact pads are connected to the host connector contact pads.
> b)SD removal sequence:
>  The card detection switch should be turned off when the SD card
>  is just going to be removed and before any SD card contact pad is
>  disconnected from the host connector contact pad.
> 
> Below is the sequence when this issue occur (Take slot gpio detection
> as example and remove the card slowly during the process):
> 1. gpio level changed and card detect interrupt triggered.
> 2. mmc_rescan was launched.
> 3. the card pads were still contacted with the slot pads because of slow
>   removal. So _mmc_detect_card_removed and mmc_rescan think card was
>   still present (cmd13 succeed).
> 4. card pads were discontacted from the card slot pads.
> So the card was actually removed finally but the card removal event
> has been missed by system.
> The interval length between step 1 and step 4 depends on the
> card removal speed. If it's longer than the detect work schedule
> delay which is 200ms, this issue will likely happen.
> 
> This patch add the card detect status check in function
> _mmc_detect_card_removed if cmd13 check succeed and host->ops->get_cd
> provided. If get_cd detect no card present then schedule another detect
> work 200ms later.
> 
> Signed-off-by: Kevin Liu <kliu5@marvell.com>
> ---
> drivers/mmc/core/core.c |   13 +++++++++++++
> 1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index b8c3d41..d9ac96c 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2290,6 +2290,19 @@ int _mmc_detect_card_removed(struct mmc_host *host)
> 		return 1;
> 
> 	ret = host->bus_ops->alive(host);
> +	/*
> +	 * Card detect status and alive check may out of sync if card is
> +	 * removed slowly when card detect switch changed while card/slot
> +	 * pads still contacted in hardware.(refer to "SD Card Mechanical
> +	 * Addendum, Appendix C: Card Detection Switch") So reschedule a
> +	 * detect work 200ms later for this case.
> +	 */
> +	if (!ret && host->ops->get_cd && !host->ops->get_cd(host)) {
> +		mmc_detect_change(host, msecs_to_jiffies(200));
> +		pr_debug("%s: card remove too slowly\n",
> +				mmc_hostname(host));
> +	}
> +
> 	if (ret) {
> 		mmc_card_set_removed(host->card);
> 		pr_debug("%s: card remove detected\n", mmc_hostname(host));
> -- 
> 1.7.9.5
>