[PATCH v3 0/2] mmc: Add power_off_delay_us support

[PATCH v3 0/2] mmc: Add power_off_delay_us support

[Judith Mendez]

This series adds power_off_delay_us support for MMC controllers,
enabling boards to specify custom delays after MMC power off to work around
hardware issues such as slow RC circuites on MMC VDD rails.

Rather than adding host driver-specific workarounds, we abstract the
implementation into the MMC core and pickup the delay value with a device
tree property (power-off-delay-us). This allows any board with slow
power off requirements to configure the necessary delay without code
changes.

The solution is minimal and follows existing patterns as with
power_delay_ms. The allowed minimum value = 0 ms (early return).
The default value is 1000us to not deviate from the
original 1ms delay set in mmc_power_off().

Link to v1:
https://lore.kernel.org/all/20260716232641.2659710-1-jm@ti.com/
Link to v2:
https://lore.kernel.org/all/20260722205701.372789-1-jm@ti.com/

Changes since v2:
- allow 0us as lowest possible value (early return)
- Change custom logic in mmc_delay_us() to use fsleep()
- drop dt parsing checkers

Judith Mendez (2):
  dt-bindings: mmc: Add power-off-delay-us property
  mmc: core: Add power-off-delay-us support

 .../devicetree/bindings/mmc/mmc-controller-common.yaml | 10 ++++++++++
 drivers/mmc/core/core.c                                |  2 +-
 drivers/mmc/core/core.h                                |  8 ++++++++
 drivers/mmc/core/host.c                                |  4 ++++
 include/linux/mmc/host.h                               |  1 +
 5 files changed, 24 insertions(+), 1 deletion(-)

-- 
2.54.0

[PATCH v3 1/2] dt-bindings: mmc: Add power-off-delay-us property

[Judith Mendez]

Add power-off-delay-us property to MMC controller common.

This property shall be used to specify value of delay after
deasserting power during MMC power cycles. Default for delay
is 1000us but custom delay can be passed in to work around
hardware issues such as slow RC discharge on MMC VDD rails.

Signed-off-by: Judith Mendez <jm@ti.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
---
Changes since v2:
- Make minimum 0 instead of 1 (for no delay, early return)
- Add Rob's review tag
---
 .../devicetree/bindings/mmc/mmc-controller-common.yaml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
index 3d7195e9461c3..8b9b3b0361296 100644
--- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
+++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
@@ -275,6 +275,16 @@ properties:
       not available.
     default: 10
 
+  power-off-delay-us:
+    description:
+      Delay in microseconds after card power is deasserted during a power
+      cycle to allow time for proper power discharge. Larger values can be
+      configured to work around hardware issues such as slow RC discharge
+      on MMC VDD rails.
+    minimum: 0
+    maximum: 10000000
+    default: 1000
+
   supports-cqe:
     $ref: /schemas/types.yaml#/definitions/flag
     description:
-- 
2.54.0

[PATCH v3 2/2] mmc: core: Add power-off-delay-us support

[Judith Mendez]

Add support for power-off-delay-us which shall be used to specify
value of delay after deasserting power during MMC power cycles.
Default for delay is 1000us but custom delay can be passed in to work
around hardware issues such as slow RC discharge on MMC VDD rails.

Signed-off-by: Judith Mendez <jm@ti.com>
---
Changes since v2:
- Drop < 0 check when parsing DT property, device_property_read_u32
  should allow only positive values. Change also per Ulf's review
- Remove upper limit check, also per Ulf's review
- Use fsleep() instead of custom logic in mmc_delay_us(), per
  Sebastian's review
- Return immediately if 0 in mmc_delay_us(), since no delay should
   now be valid as per Ulf's review
---
 drivers/mmc/core/core.c  | 2 +-
 drivers/mmc/core/core.h  | 8 ++++++++
 drivers/mmc/core/host.c  | 4 ++++
 include/linux/mmc/host.h | 1 +
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 29e80e5f928e9..9472041fe1c20 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1388,7 +1388,7 @@ void mmc_power_off(struct mmc_host *host)
 	 * XO-1.5, require a short delay after poweroff before the card
 	 * can be successfully turned on again.
 	 */
-	mmc_delay(1);
+	mmc_delay_us(host->ios.power_off_delay_us);
 }
 
 void mmc_power_cycle(struct mmc_host *host, u32 ocr)
diff --git a/drivers/mmc/core/core.h b/drivers/mmc/core/core.h
index a028b48be1644..601c73761e886 100644
--- a/drivers/mmc/core/core.h
+++ b/drivers/mmc/core/core.h
@@ -73,6 +73,14 @@ static inline void mmc_delay(unsigned int ms)
 		msleep(ms);
 }
 
+static inline void mmc_delay_us(unsigned int us)
+{
+	if (us == 0)
+		return;
+
+	fsleep(us);
+}
+
 void mmc_rescan(struct work_struct *work);
 void mmc_start_host(struct mmc_host *host);
 void __mmc_stop_host(struct mmc_host *host);
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index b7ce3137d4529..ac1846e0e7fbd 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -421,6 +421,9 @@ int mmc_of_parse(struct mmc_host *host)
 	device_property_read_u32(dev, "post-power-on-delay-ms",
 				 &host->ios.power_delay_ms);
 
+	device_property_read_u32(dev, "power-off-delay-us",
+				 &host->ios.power_off_delay_us);
+
 	return mmc_pwrseq_alloc(host);
 }
 
@@ -574,6 +577,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 
 	host->fixed_drv_type = -EINVAL;
 	host->ios.power_delay_ms = 10;
+	host->ios.power_off_delay_us = 1000;
 	host->ios.power_mode = MMC_POWER_UNDEFINED;
 
 	return host;
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index ba84f02c2a101..714417466707c 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -23,6 +23,7 @@ struct mmc_ios {
 	unsigned int	clock;			/* clock rate */
 	unsigned short	vdd;
 	unsigned int	power_delay_ms;		/* waiting for stable power */
+	unsigned int	power_off_delay_us;	/* waiting for power discharge */
 
 /* vdd stores the bit number of the selected voltage range from below. */
 
-- 
2.54.0