Re: [PATCH v2 6/7] arm64: dts: monaco-evk: Force vreg_l8a always-on to protect UFS VCC

[Sumit Garg <sumit.garg@kernel.org>]

On Wed, 12 Aug 2026 at 06:42:04 +0530, Balaji Selvanathan wrote:
>vreg_l8a is the shared VCC rail for UFS (ufs_mem_hc vcc-supply) and
>eMMC (sdhc_1 vmmc-supply). UFS holds no regulator vote of its own in
>U-Boot, so nothing stops other consumers from disabling the rail
>while UFS still needs it.

Why not teach UFS driver to keep it's regulator vote intact? Don't add
DT workarounds for this.

-Sumit

>
>eMMC's power-cycle runs after UFS has already linked up and started
>transferring data. Its power-off fires a real disable vote on
>vreg_l8a, glitching UFS VCC while the link is live. UFS has no
>recovery from this: every following command fails (OCS errors, UTP
>timeouts, "Card did not respond to voltage select! : -110").
>
>Force the rail always-on so the disable vote is rejected in
>regulator_set_enable() (-EACCES) before it reaches the RPMh driver.
>eMMC is non-removable and does not need a real power-cycle.
>
>Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
>---
> arch/arm/dts/monaco-evk-u-boot.dtsi | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/arch/arm/dts/monaco-evk-u-boot.dtsi b/arch/arm/dts/monaco-evk-u-boot.dtsi
>index 5520d111864..8e9102eae4d 100644
>--- a/arch/arm/dts/monaco-evk-u-boot.dtsi
>+++ b/arch/arm/dts/monaco-evk-u-boot.dtsi
>@@ -34,3 +34,7 @@
> 		};
> 	};
> };
>+
>+&vreg_l8a {
>+	regulator-always-on;
>+};
>
>-- 
>2.34.1
>