Some eMMCs disable their hardware reset line (RST_N) by default. To enable
it the host must set the corresponding bit in ECSD. An example for such
a device is the Micron MTFCxGACAANA-4M.
This patch adds a new mmc-card devicetree property to let the host enable
this feature during card initialization.
Signed-off-by: Richard Leitner <richard.leitner@xxxxxxxxxxx>
---
CHANGES v2:
- add RST_N_FUNCTION value to dt documentation
- set RST_N_FUNCTION only if it was not set before
---
Documentation/devicetree/bindings/mmc/mmc-card.txt | 4 ++++
drivers/mmc/core/mmc.c | 23 ++++++++++++++++++++++
2 files changed, 27 insertions(+)
diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.txt b/Documentation/devicetree/bindings/mmc/mmc-card.txt
index a70fcd6..bbfccce 100644
--- a/Documentation/devicetree/bindings/mmc/mmc-card.txt
+++ b/Documentation/devicetree/bindings/mmc/mmc-card.txt
@@ -12,6 +12,10 @@ Required properties:
Optional properties:
-broken-hpi : Use this to indicate that the mmc-card has a broken hpi
implementation, and that hpi should not be used
+-enable-hw-reset : some eMMC devices have disabled the hw reset functionality
+ (RST_N_FUNCTION) by default. By adding this property the
+ host will enable it during initialization. This will set
+ RST_N_FUNCTION to 0x1 (permanently enabled).
Example:
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index b502601..30066be 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1520,9 +1520,16 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
int err;
u32 cid[4];
u32 rocr;
+ struct device_node *np;
+ bool enable_rst_n = false;
WARN_ON(!host->claimed);
+ np = mmc_of_find_child_device(host, 0);
+ if (np && of_device_is_compatible(np, "mmc-card"))
+ enable_rst_n = of_property_read_bool(np, "enable-hw-reset");
+ of_node_put(np);
+
/* Set correct bus mode for MMC before attempting init */
if (!mmc_host_is_spi(host))
mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN);
@@ -1810,6 +1817,22 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
}
}
+ /*
+ * enable RST_N if requested (and rst_n_function is not set)
+ * This is needed because some eMMC chips disable this function by
+ * default.
+ */
+ if (enable_rst_n &&
+ !(card->ext_csd.rst_n_function & EXT_CSD_RST_N_EN_MASK)) {
+ err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
+ EXT_CSD_RST_N_FUNCTION, EXT_CSD_RST_N_ENABLED,
+ card->ext_csd.generic_cmd6_time);
+ card->ext_csd.rst_n_function = EXT_CSD_RST_N_ENABLED;
+ if (err && err != -EBADMSG)
+ pr_warn("%s: Enabling RST_N feature failed\n",
+ mmc_hostname(card->host));
+ }
+
if (!oldcard)
host->card = card;
--
2.1.4
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