linux-kernel - Re: [PATCH RFC] mmc: sdhci: Don't get card-detect without preemption

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Date:   Wed, 16 May 2018 12:50:52 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Evan Green <evgreen@...omium.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] mmc: sdhci: Don't get card-detect without preemption

On 02/05/18 02:47, Evan Green wrote:
> For a controller with SDHCI_QUIRK_NO_CARD_NO_RESET, there are several
> conditions where sdhci_do_reset is called under a spinlock with interrupts
> disabled. The card detect is often a GPIO, which might sleep. Avoid
> asking for the card detect status if interrupts are disabled to prevent
> a warning like the following:
> 
> [    2.480199] Call trace:
> [    2.480218] [<ffffff800808a698>] dump_backtrace+0x0/0x228
> [    2.480224] [<ffffff800808a8e0>] show_stack+0x20/0x28
> [    2.480235] [<ffffff80088a0214>] dump_stack+0x90/0xb0
> [    2.480245] [<ffffff80080d7aa8>] ___might_sleep+0x110/0x128
> [    2.480248] [<ffffff80080d7b38>] __might_sleep+0x78/0x88
> [    2.480260] [<ffffff80083cdd28>] gpiod_get_raw_value_cansleep+0x2c/0xc4
> [    2.480269] [<ffffff80086a93a8>] mmc_gpio_get_cd+0x3c/0x68
> [    2.480275] [<ffffff80086b008c>] sdhci_get_cd+0x20/0x98
> [    2.480280] [<ffffff80086b081c>] sdhci_do_reset+0x50/0x88
> [    2.480283] [<ffffff80086b4640>] sdhci_tasklet_finish+0x1a8/0x270
> [    2.480292] [<ffffff80080b29d4>] tasklet_action+0x90/0xf4
> [    2.480296] [<ffffff80080813b8>] __do_softirq+0x1c8/0x360
> [    2.480300] [<ffffff80080b2408>] irq_exit+0x88/0xd0
> 
> ---
> 
> I discovered this warning while trying to bring up SD, somewhat unsuccessfully,
> on a new device, and hit this error path.
> 
> This change is not ideal as it only makes a best effort to adhere to the quirk,
> but may in some cases end up resetting the controller with no card present.
> 
> Another option I considered was trying to call sdhci_do_reset within only
> sleepable contexts. I actually got as far as converting the tasklet to a
> work queue, and deferring the reset to the end of the function in
> sdhci_request_done. But 1) I'm not sure if that deferral was actually safe,
> and 2) we call sdhci_do_reset from under the lock in several other places,
> such as sdhci_card_event and sdhci_cqe_disable.
> 
> Finally, I also considered calling the non-_maysleep gpio functions in
> mmc_gpio_get_cd. I assume this is not workable as someone somewhere has put
> a card detect off of a PMIC or GPIO expander.
> 
> Any advice?

The SDHCI_QUIRK_NO_CARD_NO_RESET quirk was designed for host controllers
that use the present state register.  I have to assume that users of GPIO
card detect get away with using the quirk because:
	a) their GPIO does not sleep, and
	b) they don't enable the debugging that produces the "might sleep"
	warning

If you know your device's card detect GPIO does not sleep, then you can look
at making a non-sleep version of mmc_gpio_get_cd().

Another possibility is to look at using mmc_gpio_set_cd_isr() to keep track
of whether the card has been removed.  Also try to use sdhci_ops->reset()
rather than SDHCI_QUIRK_NO_CARD_NO_RESET.

> 
> ---
>  drivers/mmc/host/sdhci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 759278dd317d..c5273acf6987 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -210,7 +210,7 @@ static void sdhci_do_reset(struct sdhci_host *host, u8 mask)
>  	if (host->quirks & SDHCI_QUIRK_NO_CARD_NO_RESET) {
>  		struct mmc_host *mmc = host->mmc;
>  
> -		if (!mmc->ops->get_cd(mmc))
> +		if (preemptible() && !mmc->ops->get_cd(mmc))
>  			return;
>  	}
>  
>