[PATCH 3/3] sdhci-s3c: add support for new card detection methods

[akpm@linux-foundation.org (Andrew Morton)]

On Wed, 16 Jun 2010 08:49:56 +0200
Marek Szyprowski <m.szyprowski@samsung.com> wrote:

> On some Samsung SoCs not all SDHCI controllers have card detect (CD)
> line. For some embedded designs it is not even needed, because ususally
> the device (like SDIO flash memory or wifi controller) is permanently
> wired to the controller. There are also systems which have a card detect
> line connected to some of the external interrupt lines or the presence
> of the card depends on some other actions (like enabling a power
> regulator).
> 
> This patch adds support for all these cases. The following card
> detection methods are possible:
> 
> 1. internal sdhci host card detect line
> 2. external event
> 3. external gpio interrupt
> 4. no card detect line, controller will poll for the card
> 5. no card detect line, card is permanently wired to the controller
> (once detected host won't poll it any more)
> 
> By default, all existing code would use method #1, what is compatible
> with the previous version of the driver.
> 
> In case of external event, two callbacks must be provided in platdata:
> ext_cd_init and ext_cd_cleanup. Both of them get a callback to a
> function that notifies the s3c-sdhci host contoller as their argument.
> That callback function should be called from the even dispatcher to let
> host notice the card insertion/removal.
> 
> In case of external gpio interrupt, a gpio pin number must be provided
> in platdata (ext_cd_gpio parameter), as well as the information about
> the polarity of that gpio pin (ext_cd_gpio_invert). By default
> (ext_cd_gpio_invert == 0) gpio value 0 means 'card has been removed',
> but this can be changed to 'card has been removed' when
> ext_cd_gpio_invert == 1.
> 
> This patch adds changes to sdhci-s3c driver.
> 
> ...
>  
> +static void sdhci_s3c_notify_change(struct platform_device *dev, int state)
> +{
> +	struct sdhci_host *host;
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	host = platform_get_drvdata(dev);
> +	if (host) {
> +		if (state) {
> +			dev_dbg(&dev->dev, "card inserted.\n");
> +			host->flags &= ~SDHCI_DEVICE_DEAD;
> +			host->quirks |= SDHCI_QUIRK_BROKEN_CARD_DETECTION;
> +			tasklet_schedule(&host->card_tasklet);
> +		} else {
> +			dev_dbg(&dev->dev, "card removed.\n");
> +			host->flags |= SDHCI_DEVICE_DEAD;
> +			host->quirks &= ~SDHCI_QUIRK_BROKEN_CARD_DETECTION;
> +			tasklet_schedule(&host->card_tasklet);
> +		}
> +	}
> +	local_irq_restore(flags);
> +}

What's the local_irq_save() there for?

Presumably it is for local-cpu-only protection of some data.  But which
data is it there to protect?

It doesn't provide protection on SMP systems and if I'm guessing
correctly about why it was added, it would be much better to use
spin_lock_irq[save]() here.  That sets a better example, it means the
code has a hope of working correctly on SMP systems and will devolve to
local_irq_save() on UP kernels anyway.