On 9/4/2025 2:09 AM, Rob Herring wrote:
On Wed, Sep 03, 2025 at 01:34:02PM +0530, Sarthak Garg wrote:
Some platforms may require limiting the maximum frequency used in SD
High-Speed (HS) mode due to board-level hardware constraints. For
example, certain boards may include level shifters or other components
that cannot reliably operate at the default 50 MHz HS frequency.
Introduce a new optional device tree property max-sd-hs-frequency to
limit the maximum frequency (in Hz) used for SD cards operating in
High-Speed (HS) mode.
Signed-off-by: Sarthak Garg <quic_sartgarg@xxxxxxxxxxx>
---
.../devicetree/bindings/mmc/mmc-controller-common.yaml | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
index 9a7235439759..d6b785cb2bd9 100644
--- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
+++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
@@ -93,6 +93,14 @@ properties:
minimum: 400000
maximum: 384000000
+ max-sd-hs-hz:
+ description: |
+ Maximum frequency (in Hz) to be used for SD cards operating in
+ High-Speed (HS) mode. This is useful for board-specific limitations,
+ such as level shifters or others where the card cannot reliably
+ operate at the default 50 MHz HS frequency.
+ default: 50000000
Why doesn't max-frequency work for you? I would think frequency limits
wouldn't really depend on the mode.
The reason max-frequency isn't sufficient in this case is that it
applies globally across all operating modes of the SD card interface.
However, the constraint we're trying to address is specific to
High-Speed (HS) mode where the default frequency is 50 MHz.By
introducing a mode-specific property like max-sd-hs-frequency, we can
target only HS mode without affecting the capabilities of other modes.
This provides more granular control and avoids performance degradation
for other modes.
+
disable-wp:
$ref: /schemas/types.yaml#/definitions/flag
description:
--
2.34.1
