ARM: MXC: mxcmmc: work around a bug in the SDHC busy line handling

MX3 SoCs have a silicon bug which corrupts CRC calculation of
multi-block transfers when connected SDIO peripheral doesn't drive the
BUSY line as required by the specs.

One way to prevent this is to only allow 1-bit transfers.

Another way is playing tricks with the DMA engine, but this isn't
mainline yet. So for now, we live with the performance drawback of 1-bit
transfers until a nicer solution is found.

This patch introduces a new host controller callback 'init_card' which
is for now only called from mmc_sdio_init_card().

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Volker Ernst <volker.ernst@txtr.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Michał Mirosław <mirqus@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/mmc/host/mxcmmc.c b/drivers/mmc/host/mxcmmc.c
index 51e880c8f193..2c53024ee439 100644
--- a/drivers/mmc/host/mxcmmc.c
+++ b/drivers/mmc/host/mxcmmc.c
@@ -724,11 +724,27 @@ static void mxcmci_enable_sdio_irq(struct mmc_host *mmc, int enable)
         spin_unlock_irqrestore(&host->lock, flags);
 }
 
+static void mxcmci_init_card(struct mmc_host *host, struct mmc_card *card)
+{
+        /*
+         * MX3 SoCs have a silicon bug which corrupts CRC calculation of
+         * multi-block transfers when connected SDIO peripheral doesn't
+         * drive the BUSY line as required by the specs.
+         * One way to prevent this is to only allow 1-bit transfers.
+         */
+
+        if (cpu_is_mx3() && card->type == MMC_TYPE_SDIO)
+                host->caps &= ~MMC_CAP_4_BIT_DATA;
+        else
+                host->caps |= MMC_CAP_4_BIT_DATA;
+}
+
 static const struct mmc_host_ops mxcmci_ops = {
         .request                = mxcmci_request,
         .set_ios                = mxcmci_set_ios,
         .get_ro                 = mxcmci_get_ro,
         .enable_sdio_irq        = mxcmci_enable_sdio_irq,
+        .init_card              = mxcmci_init_card,
 };
 
 static int mxcmci_probe(struct platform_device *pdev)