mmc: don't request CD IRQ until mmc_start_host()

As soon as the CD IRQ is requested, it can trigger, since it's an
externally controlled event. If it does, delayed_work host->detect will
be scheduled.

Many host controller probe()s are roughly structured as:

*_probe() {
    host = sdhci_pltfm_init();
    mmc_of_parse(host->mmc);
    rc = sdhci_add_host(host);
    if (rc) {
        sdhci_pltfm_free();
        return rc;
    }

In 3.17, CD IRQs can are enabled quite early via *_probe() ->
mmc_of_parse() -> mmc_gpio_request_cd() -> mmc_gpiod_request_cd_irq().

Note that in linux-next, mmc_of_parse() calls mmc_gpio*d*_request_cd()
rather than mmc_gpio_request_cd(), and mmc_gpio*d*_request_cd() doesn't
call mmc_gpiod_request_cd_irq(). However, this issue still exists if
mmc_gpio_request_cd() is called directly before mmc_start_host().

sdhci_add_host() may fail part way through (e.g. due to deferred
probe for a vmmc regulator), and sdhci_pltfm_free() does nothing to
unrequest the CD IRQ nor cancel the delayed_work. sdhci_pltfm_free() is
coded to assume that if sdhci_add_host() failed, then the delayed_work
cannot (or should not) have been triggered.

This can lead to the following with CONFIG_DEBUG_OBJECTS_* enabled, when
kfree(host) is eventually called inside sdhci_pltfm_free():

WARNING: CPU: 2 PID: 6 at lib/debugobjects.c:263 debug_print_object+0x8c/0xb4()
ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x18

The object being complained about is host->detect.

There's no need to request the CD IRQ so early; mmc_start_host() already
requests it. For most SDHCI hosts at least, the typical call path that
does this is: *_probe() -> sdhci_add_host() -> mmc_add_host() ->
mmc_start_host(). Therefore, remove the call to mmc_gpiod_request_cd_irq()
from mmc_gpio_request_cd(). This also matches mmc_gpio*d*_request_cd(),
which already doesn't call mmc_gpiod_request_cd_irq().

However, some host controller drivers call mmc_gpio_request_cd() after
mmc_start_host() has already been called, and assume that this will also
call mmc_gpiod_request_cd_irq(). Update those drivers to explicitly call
mmc_gpiod_request_cd_irq() themselves. Ideally, these drivers should be
modified to move their call to mmc_gpio_request_cd() before their call
to mmc_add_host(). However that's too large a change for stable.

This solves the problem (eliminates the kernel error message above),
since it guarantees that the IRQ can't trigger before mmc_start_host()
is called.

The critical point here is that once sdhci_add_host() calls
mmc_add_host() -> mmc_start_host(), sdhci_add_host() is coded not to
fail. In other words, if there's a chance that mmc_start_host() may have
been called, and CD IRQs triggered, and the delayed_work scheduled,
sdhci_add_host() won't fail, and so cleanup is no longer via
sdhci_pltfm_free() (which doesn't free the IRQ or cancel the work queue)
but instead must be via sdhci_remove_host(), which calls mmc_remove_host()
-> mmc_stop_host(), which does free the IRQ and cancel the work queue.

CC: Russell King <linux@arm.linux.org.uk>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/slot-gpio.c

@@ -221,8 +221,6 @@ int mmc_gpio_request_cd(struct mmc_host *host, unsigned int gpio,
 	ctx->override_cd_active_level = true;
 	ctx->cd_gpio = gpio_to_desc(gpio);
 
-	mmc_gpiod_request_cd_irq(host);
-
 	return 0;
 }
 EXPORT_SYMBOL(mmc_gpio_request_cd);

drivers/mmc/host/mmc_spi.c

@@ -1436,6 +1436,7 @@ static int mmc_spi_probe(struct spi_device *spi)
 					     host->pdata->cd_debounce);
 		if (status != 0)
 			goto fail_add_host;
+		mmc_gpiod_request_cd_irq(mmc);
 	}
 
 	if (host->pdata && host->pdata->flags & MMC_SPI_USE_RO_GPIO) {

drivers/mmc/host/sdhci-sirf.c

@@ -116,6 +116,7 @@ static int sdhci_sirf_probe(struct platform_device *pdev)
 				ret);
 			goto err_request_cd;
 		}
+		mmc_gpiod_request_cd_irq(host->mmc);
 	}
 
 	return 0;

drivers/mmc/host/tmio_mmc_pio.c

@@ -1189,6 +1189,7 @@ int tmio_mmc_host_probe(struct tmio_mmc_host **host,
 			tmio_mmc_host_remove(_host);
 			return ret;
 		}
+		mmc_gpiod_request_cd_irq(mmc);
 	}
 
 	*host = _host;