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

[Evan Green <evgreen@chromium.org>]

On Wed, May 16, 2018 at 2:52 AM Adrian Hunter <adrian.hunter@intel.com>
wrote:

> 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.


Thanks Adrian for the guidance. I'll explore this a bit and see what shakes
out.
-Evan