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Commit 460cd058 authored by David Brownell's avatar David Brownell Committed by Pierre Ossman
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mmc_spi: Fix mmc-over-spi regression 



Patch 49dce689 changed the sysfs data
structures for SPI in a way which broke the MMC-over-SPI host driver.

This patch fixes that regression by changing the scheme used to keep
from knowingly trying to use a shared bus segment, and updates the
adjacent comments slightly to better explain the issue.

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: default avatarPierre Ossman <drzeus@drzeus.cx>
parent 1fa8dd14

drivers/mmc/host/mmc_spi.c

+33 −19
Original line number Diff line number Diff line
@@ -1165,6 +1165,23 @@ mmc_spi_detect_irq(int irq, void *mmc) 
	return IRQ_HANDLED;

}



struct count_children {

	unsigned	n;

	struct bus_type	*bus;

};



static int maybe_count_child(struct device *dev, void *c)

{

	struct count_children *ccp = c;



	if (dev->bus == ccp->bus) {

		if (ccp->n)

			return -EBUSY;

		ccp->n++;

	}

	return 0;

}



static int mmc_spi_probe(struct spi_device *spi)

{

	void			*ones;
@@ -1188,33 +1205,30 @@ static int mmc_spi_probe(struct spi_device *spi) 
		return status;

	}



	/* We can use the bus safely iff nobody else will interfere with

	 * us.  That is, either we have the experimental exclusive access

	 * primitives ... or else there's nobody to share it with.

	/* We can use the bus safely iff nobody else will interfere with us.

	 * Most commands consist of one SPI message to issue a command, then

	 * several more to collect its response, then possibly more for data

	 * transfer.  Clocking access to other devices during that period will

	 * corrupt the command execution.

	 *

	 * Until we have software primitives which guarantee non-interference,

	 * we'll aim for a hardware-level guarantee.

	 *

	 * REVISIT we can't guarantee another device won't be added later...

	 */

	if (spi->master->num_chipselect > 1) {

		struct device	*parent = spi->dev.parent;

		struct count_children cc;



		/* If there are multiple devices on this bus, we

		 * can't proceed.

		 */

		spin_lock(&parent->klist_children.k_lock);

		if (parent->klist_children.k_list.next

				!= parent->klist_children.k_list.prev)

			status = -EMLINK;

		else

			status = 0;

		spin_unlock(&parent->klist_children.k_lock);

		cc.n = 0;

		cc.bus = spi->dev.bus;

		status = device_for_each_child(spi->dev.parent, &cc,

				maybe_count_child);

		if (status < 0) {

			dev_err(&spi->dev, "can't share SPI bus\n");

			return status;

		}



		/* REVISIT we can't guarantee another device won't

		 * be added later.  It's uncommon though ... for now,

		 * work as if this is safe.

		 */

		dev_warn(&spi->dev, "ASSUMING unshared SPI bus!\n");

		dev_warn(&spi->dev, "ASSUMING SPI bus stays unshared!\n");

	}



	/* We need a supply of ones to transmit.  This is the only time