diff options
| -rw-r--r-- | drivers/mmc/host/mmc_spi.c | 52 |
1 files changed, 33 insertions, 19 deletions
diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c index 12c2d807c14..a6469218f19 100644 --- a/drivers/mmc/host/mmc_spi.c +++ b/drivers/mmc/host/mmc_spi.c @@ -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 |