[PATCH v2 1/4] mmc: Add support for disabling write-protect detection

Lars-Peter Clausen
2015-05-06T18:31:27Z

It is not uncommon to see systems where there is no physical write-protect
signal (e.g. when using eMMC or microSD card slots). For some controllers,
which have a dedicated write-protection detection logic (like SDHCI
controllers), the get_ro() callback can return bogus data in such a case.

Instead of handling this on a per controller basis this patch adds a new
capability flag to the MMC core that can be set to specify that the result
of get_ro() is invalid. When the flag is set the core will not call
get_ro() and assume that the card is always read-write.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
---
drivers/mmc/core/sd.c | 30 +++++++++++++++++++++++-------
include/linux/mmc/host.h | 1 +
2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
index 31a9ef2..8f6864a 100644
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -804,6 +804,28 @@ int mmc_sd_get_csd(struct mmc_host *host, struct mmc_card *card)
return 0;
}

+static int mmc_sd_get_ro(struct mmc_host *host)
+{
+ int ro;
+
+ /*
+ * Some systems don't feature a write-protect pin and don't need one.
+ * E.g. because they only have micro-SD card slot. For those systems
+ * assume that the SD card is always read-write.
+ */
+ if (host->caps2 & MMC_CAP2_NO_WRITE_PROTECT)
+ return 0;
+
+ if (!host->ops->get_ro)
+ return -1;
+
+ mmc_host_clk_hold(host);
+ ro = host->ops->get_ro(host);
+ mmc_host_clk_release(host);
+
+ return ro;
+}
+
int mmc_sd_setup_card(struct mmc_host *host, struct mmc_card *card,
bool reinit)
{
@@ -855,13 +877,7 @@ int mmc_sd_setup_card(struct mmc_host *host, struct mmc_card *card,
* Check if read-only switch is active.
*/
if (!reinit) {
- int ro = -1;
-
- if (host->ops->get_ro) {
- mmc_host_clk_hold(card->host);
- ro = host->ops->get_ro(host);
- mmc_host_clk_release(card->host);
- }
+ int ro = mmc_sd_get_ro(host);

if (ro < 0) {
pr_warn("%s: host does not support reading read-only switch, assuming write-enable\n",
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index b5bedae..3b92fd4 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -285,6 +285,7 @@ struct mmc_host {
MMC_CAP2_HS400_1_2V)
#define MMC_CAP2_HSX00_1_2V (MMC_CAP2_HS200_1_2V_SDR | MMC_CAP2_HS400_1_2V)
#define MMC_CAP2_SDIO_IRQ_NOTHREAD (1 << 17)
+#define MMC_CAP2_NO_WRITE_PROTECT (1 << 18) /* No physical write protect pin, assume that card is always read-write */

mmc_pm_flag_t pm_caps; /* supported pm features */

--
1.8.0