mmc_spi: Fix mmc-over-spi regression
Patch 49dce689ad4ef0fd1f970ef762168e4bd46f69a3 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: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index 12c2d80..a646921 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1165,6 +1165,23 @@
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 @@
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
